'95 cutlass cruiser missing/bucking under light load on interstate

[John B.]

I have a 95 cutlass cruiser, it's a beatiful car in great shape, but it has this annoying problem my mechanic can't fix. Driving around town is fine, no problems at all. But if I take it out on the interstate or any road where I can get it up to around 60, if I start up a slight grade and have to apply light pressure to the gas pedal it starts to jerk, or buck, or miss. It's usually pretty slight, but most people would notice. Under heavy throttle there doesn't seem to be any problem. Another thing I noticed which may or may not be related is that at idle I notice the engine seems to misfire maybe once every minute or so, just a slight shake that most people wouldn't notice. I've already changed the spark plug wires which was the cause of an almost identical problem on my 90 celebrity, but in this case, it didn't help. Plugs have about 20,000 on them and they were supposed to be good ones. My mechanic replaced the fuel filter, air filter and a solenoid in the transmission, but those things didn't help at all. Thanks!

[86euro]

Has your mechanic tested the fuel pressure?

[Duke George V]

Generally when it's a driveability issue it's either fuel or spark that's lacking. Have you done the ignition coils or ignition control module? Are the fuel injectors clogged?

[notsoslimshady76]

I agree with Duke George

[Pontiac6ksteawd]

I have had that same problem, and it ended up being a TCC solenoid. try leaving your foot on the gas, while its bucking, and gently apply pressure on the brake pedal. Dont push it down to far, about 1/4-1/2 inch, just enuf for the brake lights to come on. And see if the bucking stops.

[John B.]

Does the TCC solenoid have something to do with the torque converter? My mechanic did replace that, but it didn't help. He said I might have to end up replacing the torque converter. I don't think the fuel pressure was checked, but if I don't have problems under hard acceleration wouldn't that eliminate fuel pressure as the problem, since that's when it uses the most fuel?

[Tonglebeak]

The TCC solenoid engages lockup. Locks the torque converter up so there's virtually no loss through it. RPM drops a bit and power transfer is more efficient.

[86euro]

I don't think the fuel pressure was checked, but if I don't have problems under hard acceleration wouldn't that eliminate fuel pressure as the problem, since that's when it uses the most fuel?

Here's the way my simple mind looks at it: At a higher RPM, the motor has more momentum to roll right through the "hiccups" so it's not noticeable... it just leans out and lacks power.
This has happened to me with a few vehicles that had drivability issues until the fuel pump finally died. With a new pump they ran like a top and I was amazed how much power had been lacking previously.

[Tonglebeak]

I want to add, when the fuel pump in my work's astro took its last breaths, normal acceleration worked just fine, but as soon as heavy or wot was applied, the pump would nearly quit working and provide any acceleration at all (you could hear the engine quietly breathe a huge amount of air and not combust, it was actually quite amazing)

[Electra_T_Type]

Oh god this sounds like the probelm with my moms car. I hope the fuel pump doesn't die, again .

[85_Ciera_Rebuild]

I don't think the fuel pressure was checked, but if I don't have problems under hard acceleration wouldn't that eliminate fuel pressure as the problem, since that's when it uses the most fuel?

Anytime a driveability issue comes up....Fuel Pressure and fuel regulator needs to be checked: But, on 2.5 TBI motor (I assume you have TBI), I have never messed with TBI.

Hard acceleration would open the injector more on a continuous fuel injection TBI....but at light foot applications, there could be a problem with fuel flow due to various reasons (fuel pump, injector, fuel pressure regulator, etc).

My suggestion is to try some of that injector cleaner first....and then if this does not work, find someone who knows TBI.

[85_Ciera_Rebuild]

if I start up a slight grade and have to apply light pressure to the gas pedal it starts to jerk, or buck, or miss.

Those are classic symptoms of a Lean Mixture, btw....but, why is another story....either too much air is getting in, or not enough fuel...which it is, I don't know.

[John B.]

My car has the 3.1 V6 with the overdrive automatic. I see that I failed to mention that. So, I don't believe I have TBI. My dad thought my problems were caused by water in the fuel. I thought that was very unlikely but I did put some kind of fuel treatment in and it made no difference at all.

[Duke George V]

My car has the 3.1 V6 with the overdrive automatic. I see that I failed to mention that.The multiport engines are known for eating fuel injectors every so often, and that produces the same symptoms you're describing. I just went through this with my Celebrity, but I had to cheap out and only replace a coule of them. I highly recommend doing all six, even though it won't be cheap—$70 each injector, around five hours of shop labor, and x for a upper intake manifold gasket. GM actually calls for replacing the ECM as well, just to eliminate all possible issues.

...oh wait, yours is a '95, which is NOT multiport, but is in fact SFI. *forehead slap* Still, as old as it is, I'd be surprised if it wasn't fuel injectors.

[Pontiac6ksteawd]

Wouldnt be injectors I dont think. The 95 models had a second gen model injector. Which is 10x better than our MPFI injectors. Fuel pressure check, TCC check, and maybe a clogged exhaust check.

[85_Ciera_Rebuild]

My car has the 3.1 V6 with the overdrive automatic.

Then, if you have an old R-12 low-side gauge, hook it up to the schrader valve-port, and see what:

1. Idle fuel pressure is

2. Idle fuel pressure with vacuum disconnected on pressure regulator

3. Turn off key, and see how long it takes to bleed pressure down

This test does not take much time...and I assume your vehicle has a schrader valve-port.

PS: Check your local pawn shops for an used R-12 gauge

[Jr's3800]

When the car starts to stumble of miss, does this happen around town in stop and go traffic?

Do you notice the miss at 37-39 Mph when the PCM locks the TCC in 3rd gear... Also wonder if its more pronounced for you in 4th gear( OD )..

Like stated above what is the fuel pressure?

Also when was the last time the plugs and wires were replaced and what kind of plugs were used?

[John B.]

I have to ask....what is SFI? I thought this car had multiport FI like my old Celeb??? To answer some of the questions you are asking....it seems to drive fine around town although I'm starting to notice the intermittent missing at idle more and more. I haven't tried it lately, but I think it did the same thing when I tried not using the overdrive. I really don't notice the bucking/missing/jerking unless I'm going over 40, but oddly, it doesn't seem to do it if I'm going REALLY fast, like close to 80. I just replaced the spark plug wires, they're brand new. The plugs have about 20k on them. I don't know what kind they are but I asked my mechanic to put GOOD ones in so I'm sure he didn't use Champions. I just talked to my mechanic again today and he's now leaning towards bad gas, but I use the same gas in my '94 Century and that doesn't have ANY of these problems. Sigh..... Maybe I should try some good fuel injector cleaner???

[Jr's3800]

SFI is Sequential Fuel Injection.. With the SFI system the PCM will fire each injector individually and the timing of the injector pulse will be pretty accurate and timed with the valve sequence.. So the PCM has a driver for each injector..

Ok generally when you replace the plug wire you replace the plugs as well..

If your mechanic used a Bosh Platinum Plug, you will have skips and stumbles with 20k on them... But I am not sure what he used.. Champion would have been better than Bosh Plats tho..

It does sound to me like an ignition related issue.. You will notice the miss the most at about 50 Mph with the TCC locked and the engine under load..

I'd still like to know what kind of plugs are in it...

[John B.]

I just checked the plugs and they are Bosch Platinum.

[Jr's3800]

I just checked the plugs and they are Bosch Platinum.

That will be the Problem...

You do not want to use Bosh Platinum Plugs with a GM DIS system...

When you get them out... Take a look a all 6 of them... Especially the insulator you notice that the Platinum tip has been eroded away..

I am surprised you got 20k before trouble..lol

I would recommend an AC Delco, NGK or Autolite plug for you car..

[John B.]

You sound pretty sure about that. I will have them replaced as soon as I can get around to it and I will try to remember to post a message with the results. Thanks.

[Jr's3800]

I am never 100%... Its hard to be when you can't look at the car in question..

But Most of the GM DIS systems will not react too well in the long term to Bosch Platinum Plugs.. I have seen these Plugs fail even in the GM HEI Distributor systems as well..

Judging by the fact that you have 20k on the Platinums I'd have to say they are done...

The GM DIS used on the 2.8,3.1,3100's, 3400... All 3800's, are all Waste Spark systems.... Yes the system actually wastes a spark...

It takes very little to fire the plug on the exhaust stroke, so the rest of the energy is used to fire the plug on the compression stroke.... If one of those plugs is unhappy the GM DIS system can get very grumpy as it will not be able to function as designed...

This would be a very cheap fix for you to try... After 20K it may be well worth your while...

I do recommend AC Delco or NGK for your car.... Let us know how it turns out..

If you live near Central FL, drive on over and I'll help you..:)

[Pontiac6ksteawd]

Do the AC Delco plugs. I think your car will be happy you did.

[John B.]

I wish I did live near central Florida, but I live up in PA. I will let you know if that fixes the problem. I have a good feeling that it will.

[85_Ciera_Rebuild]

I just checked the plugs and they are Bosch Platinum.

Any photo of one?

I've never had a problem with Bosh Platinum Plugs on 87 Olds 3.8 motor...or SBC motors.

But, I prefer to replace plugs with platinum...be it AC, Ford, or who ever...I wouldn't spend much over $2.00/plug either....better to replace them some 50,000 miles later, imho.

[Jr's3800]

Any photo of one?

I've never had a problem with Bosh Platinum Plugs on 87 Olds 3.8 motor...or SBC motors.

But, I prefer to replace plugs with platinum...be it AC, Ford, or who ever...I wouldn't spend much over $2.00/plug either....better to replace them some 50,000 miles later, imho.

How long did you run on those Plugs?

After years of tinkering with various cars and trucks The Bosh Platinums were by far the worst.. I'd use an R44LTS6 or R45LTS6 in my LN3 3800's brfore I'd touch a Bosh Plug... Same goes for the SBC, I's use AC Delco...

Over on the other Forum we have watched people use the Bosh Platinums... After years of keeping track of the Failures on the Bosch Platinum Plugs we have found they they frequently fail in the GM line of cars....

In Hanging out with My shade tree friend... We actually got to a Point that when someone brough us a GM Car or Truck and said it wasn't running right or felt like it was missing, the first thing we checked was to see what kind of plugs it had in it..

Funny part of the story... Back in the early days( 9-10 years ago ) we both tried the Bosch Platinums, He put them in his 3.0 HO Buick V6 in his Grand Am, and I put them into my 95 3800 Series II V6... Down the road his car started to miss and skip a little.. we yanked the Plugs and saw the Platinum tip eroding away.... I made a trip up home and back and noticed my car was not running quite right either... Again we went to the Parts store and I picked up my AC Delco 41-606 plugs and we pulled the Platinums... Sure enough it had eroded the platinum tips.. We have seen this time after time on the Forum I frequent, as well as my Shade Tree friend who works on everything...

If there is one plug we steer clear of its the Bosh Platinum.... We also stay far away from the Bosch O2 as well... But thats another story..


I hope I am not coming off in a bad way at all, and anyone is free to run any Plug they want.. But I do recomend AC Delco or NGK.. Autolite, Denso and the like are also pretty good Plugs...

Good Luck

[85_Ciera_Rebuild]

How long did you run on those Plugs?....The Bosh Platinums


A vehicle with 3.8 motor I sold has some 60,000 miles since I replaced its plugs, and it passed Denver Emission Test this year....just barely (about 200,000 total miles on motor).

1982 Chevy SBC (V8) had some 70,000 on it when I replaced them again (200,000 mile vehicle).

1986 Chevy SBC (V8) had some 60,000 miles on them before I replaced them again; I replaced them when I replaced valve stem seals this year. (160,000 total miles on it).

After about 50,000 miles is a good time to replace standard platinum plugs.

Before platinum plugs on GM's HEI system, the gap would widen to around 0.07, and you would have drivability issues...as in motor would shut down while on highway...and restart fine.

In older days, 1969 era big block motors (396..) running premium, about every 10,000 miles you replaced plugs, wires, points, cap, if you wanted peak performance.

I live in rural area, and mice are my biggest problem...they chew those soft spark plug wires...

On my 88 Beretta, I was going to replace plugs when I first got it, but discovered the previous owner had done this with AC plats...so I only checked the gap, and left them in there.

I might mention that the plugs I remove, I've looked at....and I've never seen anything unusual about Bosch plugs....but I don't drive high compression motors....unleaded fuel vehicles...and all of these vehicles have/could startup in cold weather (about zero conditions).

[Jr's3800]

I have seen a lot of Platinums in a lot of different motors and that includes my own cars..

Ac Delco, Autolite, NGK, Denso... On and on... Most all of them will live a very good long extended life... I have seen them at 50k not look so wonderful, but they could live on with a simple regap..:)

The Bosch Platinums are another story in electrode design... I have seen too many of the Bosch Platinums fail to the Point I would even use them in an Enemies car...lol

I have NGK Platinums in my 3800 right now... I have ran AC Delco Rapidfire #14 Plats in my car before and had good results... as a matter of fact I believe that they took that very design and use them in most of their cars and trucks today..:)

[Electra_T_Type]

Personally I ude the AC Delco Rapidfires, but I think I heard they've been discontinued.

[Pontiac6ksteawd]

The good ones have been. And the replacement rapids are junk...

[Electra_T_Type]

Damn, I really like how they work especially after taking out the Bosch +4 put in by the previous owner, what would be a sutible replacement?

[John B.]

I'm confused, I thought platinum plugs were supposed to last a lot longer than regular plugs. That's why I wanted them for this car in the first place so I wouldn't have to get them replaced soon. But yet I only have 20k miles on these and they seem to be shot. Why? I've had conventional plugs run over 60k with no noticeable problems. I decided to get AC Delco's for this car and I went to their website and their platinums have a 100k mile warranty while the conventionals only have a 12k warranty. If I want the longest lasting plugs for this car, what should I get? I think I've ruled out the iridiums though--not keen on spending $10 per plug. Thanks!

[Jr's3800]

Get the AC Delco, NGK or Autolite Platinums...

Bosh Plats burn out early with the DIS system...

Its not so much that its a Platinum plug, but the design of the Plug.. :)

[85_Ciera_Rebuild]

...annoying problem my mechanic can't fix....around 60, if I start up a slight grade and have to apply light pressure to the gas pedal it starts to jerk, or buck, or miss...

After thinking about this:

1. O2 Sensor - Replace it, if more than 30,000 miles since last replacement
2. I assume no Codes exist
3. Coolant Temperature Sensor - An ohm meter can be used to test this

I will assume your fuel pressure and regulator are fit; good to go.

[85_Ciera_Rebuild]

Personally I ude the AC Delco Rapidfires, but I think I heard they've been discontinued.

RapidFire® Spark Plugs (http://www.acdelco.com.au/spark_plugs.htm)
ACDelco RapidFire® Spark Plugs have been designed for the
improved performance that your vehicle demands, quicker throttle
response, longer life and optimum efficiency.


Professional Platinum Spark Plugs
ACDelco's range of full platinum spark plugs has a surprisingly
comprehensive coverage of various applications with only nine
part numbers. A notable inclusion is the platinum spark plug for
Gen III V8 applications.


Designed to last for a minimum of 100,000 kilometres.

[Pontiac6ksteawd]

I dont care if the plug claims to last for 100k miles. On our cars, IT WILL NOT HAPPEN. The plug doesnt like our HEI systems, or the style of the bowl where the plug extends barely out into the combustion chamber. Plat plugs have certain requirements for them to work properly, and in our cars, it aint gonne happen. Point, check, case closed.

As far as the rapidfires goes. They had Gen 1 rapidfires, and Gen 2 Rapidfires. The gen 1 RF's are what alot of tuner, and sport enthusiasts use, and try to find. Its a better design, last longer, and the claims of how the plug works are true. But, The gen 2 RF's, which is the only thing you can get now, are pure junk. Dont work as they claim, and are better suited in a trash can.

[85_Ciera_Rebuild]

I dont care if the plug claims to last for 100k miles
...

100,000 Km = 62,137 miles

So, Mr. Goodwrench says their "Professional Platinum Spark Plugs" are good for 62,137 miles, or 100,000 Kilometers, which is the same distance.

I say, pull them out at about 50,000 miles and replace them....I've gone longer...but, your mileage will vary.

Like I said, in the old days, with higher compression motors, you yanked them out at around 10,000 miles.

OEMs do make changes overtime....I've never had these problems....but, I'm a light-foot when it comes to throttle response....so, I would not know about effects with high rpms.

[Jr's3800]

I am anal about Plugs, wires, Filters, Oil changes and the like...

I usually do 1 year on AC Delco Copper Plugs, or NGK TR55 Copper plugs.... The Most I ever went on a Delco Platinum was 2 years....

I have the NGK TR55 Platinums in 2 3800's right now... I seriously doubt I'll have them in there in 2 years... I usually just buy a handfull of the NGK TR55 Coppers and change then when I fell its time for them to be changed..... But I also run the cars hard..

I would not let even a set of Platinums go more than 60,000 miles.... And even by then they are usually pretty well worn...

If you are anything like me its worth you $$ to just get a regular set of plugs..

Also keep in mind each coil will fire both plugs.... So all of the Plugs are being fired 2 times more than other cars and or trucks.... So if you look at it the plug will be fired on both the compression/power stroke and the exhaust stroke..

[John B.]

I just went to my local auto parts store to pick up some AC Delco platinum plugs for this thing, and they said they didn't carry them. So, I asked for NGK platinums, but they were out of stock. So I ended up getting Autolite platinums. I supposed to be getting them put in tomorrow so I'll let you guys know if that fixes the problem. I hope it does, cuz it's getting really bad now. It misses badly when idling and when cruising down the road at any speed.

[85_Ciera_Rebuild]

getting Autolite platinums....misses badly when idling and when cruising down the road at any speed.

Disconnect the O2 Sensor...and drive it...never tried it this way, but it should put the ECM into Open Loop Mode, which is factory settings.

Also, if its been more than 30,000 miles, replace the O2 Sensor:


Problems arise, though, when the O2 sensor is no longer able (http://www.bennettauto.com/oxygen_sensors.html)to respond that fast, or to measure accurately the amount of oxygen in the exhaust. Under those conditions, the engine no longer operates efficiently and rich or lean conditions can occur for protracted periods of time.

The result is poor driveability, manifested by one or more of the following symptoms:

· decreased fuel economy
· hesitation on acceleration
· stalling
· surging
· rough idle and
· increased tailpipe emissions (with a likely failure of emissions tests, where mandated).

In addition to driveability problems, a faulty O2 sensor can lead to premature failure on the catalytic converter.

The most common causes of early sensor failure are deposits on the probe tip that prevent the tip from accurately measuring the amount of oxygen in the exhaust gas. Silicone, condensed water, and some oil additives can contaminate the sensor.

In addition, sensors can be subjected to extreme temperatures, oil fouling, carbon deposits, and the corrosive effects of a myriad of harmful chemicals during a "normal" life. Eventually, even the best oxygen sensor, operating in the cleanest engine, will wear out.

[85_Ciera_Rebuild]

slight grade and have to apply light pressure to the gas pedal it starts to jerk, or buck, or miss....Under heavy throttle there doesn't seem to be any problem.


For a Toyota Computer, it goes into Open Loop with cold engine, acceleration, deceleration, moderate to heavy load conditions, and wide open throttle. It works in Closed Loop only with engine warm for idle and cruise conditons (and if all sensors are working).

If GM works this way also, then:

1. Oxygen Sensor
2. Mass Air Flow Sensor

may be related to your problem since you are saying it only happens during warm idle and normal cruise.

O2 sensor has to be replaced, but you can try to clean off your Mass Air Flow Sensor.

I'm not familiar with 1995 3.1 motor....but if it has a MAF, check to see if it can be cleaned off with a MAF sensor spray (about $6.00).

If you disconnect your O2 Sensor, the engine should be running in Open Loop when warm....if GM's Open Loop program has good fuel/air data points, your vehicle will run a richer mixture....if GM's Open Loop program has good fuel/air data points. Try IT.

[Pontiac6ksteawd]

100,000 Km = 62,137 miles

So, Mr. Goodwrench says their "Professional Platinum Spark Plugs" are good for 62,137 miles, or 100,000 Kilometers, which is the same distance.

I say, pull them out at about 50,000 miles and replace them....I've gone longer...but, your mileage will vary.


Do you really beleive everything you read? If a sign said that your car will get 100mpg if you drove it off a bridge, are you going to do it? Probly not.

As I said befor, and I will say it again. The platinum plugs will not last anywhere near 100k miles in our cars because the engine is NOT designed for it. Doesnt matter if you have a light foot, heavy foot, use premium gas, whatever. I really could go into why this is, but I really dont feel like explaining it to you, because you seem to throw everything I say back at me because you read somewhere that its different. I hate to tell you this, but it just aint so...

No engine made befor 1996 is designed to have a platinum plug. It doesnt matter if its a Toyota, Ford, Mitsubishi, Dodge, Chevy, etc, The engines are plainly not designed to run a platinum plug. You will find a FEW exceptions to the rule, but not many ppl on this board are driving BMW's, Benzos, or Twin Turbo Nissans.

[Jr's3800]

For a Toyota Computer, it goes into Open Loop with cold engine, acceleration, deceleration, moderate to heavy load conditions, and wide open throttle. It works in Closed Loop only with engine warm for idle and cruise conditons (and if all sensors are working).

If GM works this way also, then:

1. Oxygen Sensor
2. Mass Air Flow Sensor

may be related to your problem since you are saying it only happens during warm idle and normal cruise.

O2 sensor has to be replaced, but you can try to clean off your Mass Air Flow Sensor.

I'm not familiar with 1995 3.1 motor....but if it has a MAF, check to see if it can be cleaned off with a MAF sensor spray (about $6.00).

If you disconnect your O2 Sensor, the engine should be running in Open Loop when warm....if GM's Open Loop program has good fuel/air data points, your vehicle will run a richer mixture....if GM's Open Loop program has good fuel/air data points. Try IT.

When a GM gets to a certain Temperature it will then be in closed loop mode... You could unplug the MAF or the O2 and the management system will still be in close loop but will not be able to run properly and throw several codes..

Unplugging the O2 will only piss off the PCM as the PCM will simply thinks it sees a bad or dead O2 and will throw O2 codes and then it will go to a generally rich default as it can't determine what its doing for fueling.... It will run rich enough for it to foul out the plugs, which at that point will be gassed out and have to be replaced..

I was working on a GM that was fouling out Plugs.... They were coming out black as tar.... Chech engine light was on... Scanned it for codes and live data.... Sure enough an O2 code popped up.... Viewed the live data and what do you know.... Dead O2... I went to pull the O2 to have a look at it and Lo and Behold it was unplugged as well as a few other wires out of place....( Its my theory that some had put a new motor in and forgot to plug the O2 back in ).... Even if an O2 was on the way out I wouldn't just unplug it...

[85_Ciera_Rebuild]

Do you really beleive everything you read? If a sign said that your car will get 100mpg if you drove it off a bridge, are you going to do it?


Well, actually, I did get 100 mpg coming down Trail Ridge Road (http://www.rmnp.com/RMNP-Areas-TrailRidge.HTML).

.
.

Now, lets get down to spark plug basics:
.
.
Bosch Speak:

Q. How does Bosch test engines to determine the heat range and what heat range should I use? (http://www.euromotoelectrics.com/BOSCHSPFAQ.pdf)

A. To ensure optimal performance in your car, Bosch has tested each vehicle model and the various engines available for that model listed in the Spark Plug catalog or our web-page. Using a special spark plug with a thermocouple built in, Bosch engineers find the hottest cylinder in an engine and then test various spark plugs in that cylinder until the ideal plug is found. This ensures that you will always get the best performance possible.

So, Bosch Speak says they evaluate each engine via "hottest cylinder." Needless to say, if your engine is not upto OEM specs, you would be running a colder plug.

So, if it is possible to increase the heat range in a Bosch plug for your engine, then you would be getting a hotter spark. But Bosch has to cover its tail, cause if you drive some 3,000 over the road miles, and your engine breaks down, due to hot plugs, they might get sued.

Hence, if you are driving locally, especially in a cooler environment (like say Colorado), you may want to increase the plug's heat range, and get a hotter spark.

I did this on air-cooled motorcycles for years; when going on a long trip, I installed a colder plug, but when driving locally (no constant heavy loading), I installed hotter plugs.

If the plug's heat range is off, for your motor/conditions, you will/might have problems.

[Jr's3800]

I will say this and then I have nothing further to add to this thread..

A Bosh Platinum Plug is very different from a Regular Bosch Plug...

I will not recommend a Bosch Platinum Plug, Will not recommend a Bosch O2 sensor or Bosch Plug wires... We have found that all of these items suck...

That being said Bosch does have good products and Millions of GM cars use those Fuel Pressure regulators and Fuel injectors and they function fine...

On the plugs take it as you will...

If I see a Bosch Platinum in a GM I will take them out and throw them in the trash...

Good Luck Guys:)

[85_Ciera_Rebuild]

Unplugging the O2 will only piss off the PCM as the PCM will simply thinks it sees a bad or dead O2 and will throw O2 codes and then it will go to a generally rich default as it can't determine what its doing for fueling....


Yes...this was a test....if his vehicle does not have these problems....then we know something.

My understanding is when 02 sensor is defective, computer will use pre-programmed values, which are richer fuel settings....which is what you stated.

This was only a test....if it runs much better....then its not the spark plugs...maybe MAF/O2.

[John B.]

Well here's a new twist to the problem....yesterday the car ran like crap, missing constantly while idling and driving down the road--probably the worst it's been since I noticed this problem. Last thing I did before parking it last night was fill up the gas tank. Today, it runs better than it has in months--almost perfect in fact. I got the new plugs and I was going to have my mechanic put them in today, but we decided maybe I'd drive it a while longer and see if there's a pattern such as full tank=runs great, near empty tank=runs like crap. It's not just a bad tank of gas though, the cars been doing this for 6 months.

[85_Ciera_Rebuild]

... fill up the gas tank.


I don't know your Geo Location, but if Amoco is around with their premium, put a full tank in...there is a good injector cleaner out there, but it cost around $6.00...I'd have to go find it to say its name.

Amoco has standards, and they make sure their stations are within their standards...last I knew.

[Tuddi]

Has someone been playing with acetone in excessive amounts in the gasoline in this car?

Acetone is "ok" to use in minute amounts in the gasoline. It cleans out the engine, but it can f*ck up the different sensors in the engine, and cause the car to be terrible for MONTHS afterwards. Acetone is promoted as an additive for gasoline (and is indeed in many octane booster additives) ... but it is wery easy to get on the wrong side of what's tolerable for the car (even a single ounce exceeding the recommended amount) in a 20 gl tank can make you wish you never tried it out).

I've been there... and it's not something I will be playing with again.

[Pontiac6ksteawd]

Bosch Speak:

Q. How does Bosch test engines to determine the heat range and what heat range should I use? (http://www.euromotoelectrics.com/BOSCHSPFAQ.pdf)

A. To ensure optimal performance in your car, Bosch has tested each vehicle model and the various engines available for that model listed in the Spark Plug catalog or our web-page. Using a special spark plug with a thermocouple built in, Bosch engineers find the hottest cylinder in an engine and then test various spark plugs in that cylinder until the ideal plug is found. This ensures that you will always get the best performance possible.

Bosch speak for ppl that have experience with these plugs in our cars. Yes Bosch tested these plugs in many diferent cars and engines, made from 1996 on. You really think they care about a engine that is some 10 years old when they made these plugs? or even a car that was 4-5 years old when these plugs were designed and made. No they dont. Our cars dont contain the diagnostic equipment to do diagnostics on the run that actually reads how each cylinder is firing. Our cars do diagnostics after the fact, how the O2 sensor reads this, or the EGR, or whatever. But not each individual cylinder. If you have a 3100, 3800, or a 3400, you might be ok. But not a 3.1, 2.8, 3300, or 3.8.

Heres how it works in simple terms, Bosch designs a new plug, bosch calls GM/Ford/Whoever to see if they can use one of their engine/s to test a new plug, they reply that they have a NEW engine that they can test these plugs on, if they can also use the data to better design there engines, and their own plugs. Notice how I said new? not a engine thats 10 years old. I worked for Ford, I KNOW THIS IS HOW IT WORKS.

Simply put. Dont put any type of Plat plug in your car that is a 3.1, 2.8, 3300, or 3.8. You will eventually run into problems. Depending on driving habits, anywhere from 10k miles, up to 30k, and if you are really lucky, 60k miles (Bosch advertises for 100k MILES here in the states). So I can put 9 bucks into getting a set of standard AC Delco plugs, that WILL last me 30-40k miles, OR, I can get a set of plats for 30 bucks, that will last me about 14k miles... hmmm... Thats some pretty easy math right there.

[Tuddi]

Plug changing time for me tomorrow. 22 year old 2.8 carbed engine. What is it I should be looking for as the primary choice?

[Pontiac6ksteawd]

I always recomend the stock factory plug Tuddi. I have gotten the longest life out of them, with the fewest problems.

[Tuddi]

Brand name? I am pretty sure the plugs I have now, are as far from being original ones as I am away from walking on Mars.

[LordDurock]

were the shift point for 3 gear. at what mph

[85_Ciera_Rebuild]

What is it I should be looking for as the primary choice?

Visually check your plugs...to determine if a higher or lower heat range is in order.

[Pontiac6ksteawd]

Brand name? I am pretty sure the plugs I have now, are as far from being original ones as I am away from walking on Mars.

I would recomend AC Delco, Autolite, Champion, but just in a standard plug.

Did you ever get your carb all figured out, I remember you were haveing problems with it befor..

[85_Ciera_Rebuild]

Simply put. Dont put any type of Plat plug in your car that is a 3.1, 2.8, 3300, or 3.8.


When I changed Valve Cover seal and Timing Chain Cover gasket on 88 Beretta a month ago, I checked visually every plug on this 2.8 motor; they were stock AC-Platinums.

All six were operating within the "spark plug self-cleaning temperature," as explained in post four here (http://www.a-body.net/forums/showthread.php?p=3854#post3854).

If your spark plugs are running in the "spark plug self-cleaning temperature," then it don't make a hoot which brand you use...if they are not running within the "spark plug self-cleaning temperature," then you need to change the heat range used.

Spark plug self-cleaning temperature means if your plugs are not within this temperature range, you got problems.

Visually check your plugs....it tells the whole story...

[LordDurock]

the more i read this thread the more i like deisel...............
if you plugs are bad replace them with AC ones they seem to work the best in gm cars. if you have a dis cap check for arc trails.

like 85 said vicaily check your plugs. and if there okay check the gap. i think the gab should be .35 but dont take my word for it.

[Pontiac6ksteawd]

John B. I hope we didnt run you off here. We were talking about your car, and, it took a turn for this that and the other. So where are we at on your car? Its posible you just had some bad gas in there, which cleared out with the new tank of gas. If this is the case, I would like to recomend a bottle of HEAT, and maybe a small bottle of a fuel injector cleaner. See how that goes. Not sure where you have been getting your gas, but maybe a diferent station is in order. In ground tanks have issues with water seapage, and this could be your issue. Run a tank of premium in the tank as well to dilute the impuritys that might still remain in your tank. If this solves your problem, I would lastly like to recomend a new fuel filter. Let us know man...

[John B.]

Yeah, I asked about spark plugs and then everyone went off on a tangent, but that's ok, I absorb all the information that comes my way. As for my car....2 days ago it ran like crap, missing badly at idle and driving down the road. Yesterday, with a full tank of gas, it really ran very well. Last night I put a bottle of STP gas treatment into the tank (it says it removes water) and today the car runs great down the highway but idling is really rough and unsteady (speeding up and slowing down) but it's not missing like before. So now I am leaning towards maybe there is just some junk in my gas tank that needs to be cleared out. I appreciate all the advice I get from you guys....I just hope that it might help others as well!

[Tuddi]

I would recomend AC Delco, Autolite, Champion, but just in a standard plug.

Did you ever get your carb all figured out, I remember you were haveing problems with it befor..

Well, I went to look for either AC Delco or NGK's. Had with me the part numbers for both brands (3-4 different for each brand). After checking with 4 sparepart shops with "extensive" stocks, I finally accepted their verdict: The product codes used in the US are a totally different system from what they have here. They didn't even list the a-bodies in the catalogues. Finally I was ready for a compromise, went for an old and dusty Champion catalogue, found the product number I needed... the clerk went to search their stock and came back with a plug (http://store.summitracing.com/partdetail.asp?autofilter=1&part=CPN%2D25&N=700+321013+115&autoview=sku)that is a little hotter than the one listed (http://store.summitracing.com/partdetail.asp?autofilter=1&part=CPN%2D18&N=700+321013+115&autoview=sku). Rather than continue the search, I bought those and have replaced the old Autolite 26 plugs, which were also not the correct fit.

Here are pictures of the ones I pulled from the car.








I can't seem to be able to correctly place them in the chart provided here:

http://www.4secondsflat.com/plug_chart.html

The carb issue is still not fully solved... or the ignition for that matter... I'm not going to be out of work for as long as I have that car... that's for sure :)

[Pontiac6ksteawd]

Tuddi, yours look to be number 11 on that list. So it looks like it wasnt to bad.

John, Sometimes bad gas can just foul up a plug to no end. A tune up my ultimately be in order. You can try other things, a good WOT on a warm engine up to about 70 mph. Clear the soot and carbon out, and see what happens.

[LordDurock]

yuck good luck withthe camps every on i know is terbale luck with them.
what ever you do dont do that water trick some on posted.<--------scary

[Tuddi]

idling is really rough and unsteady (speeding up and slowing down) but it's not missing like before.

This sounds exactly like what my car is doing.

If I adjust the idle screw on the carb, it still speeds up and slows down. Changing the spark plugs did not solve that issue at all. I have had the carb totally disassembled and cleaned, and that did not solve the issue either.

The gasoline filter is new and the one I had before that only served for a couple of months (changed for a bigger one) and it did not have any dirt visible in the filter (it had a transparent plastic housing).

I rather think it's ignition related.

[85_Ciera_Rebuild]

I can't seem to be able to correctly place them in the chart provided here:


Read Completely Example #1, it may be relevant.

Plug Reading - Gas Engines - 4 Stroke (http://www.4secondsflat.com/Spark_plug_reading.html)

I understand yours has a Carburetor....I would expect a pinch richer mixture than with later year vehicles with injectors....does it have an "electronic needle(s)" that go up/down on it to control fuel? Mixture Control Solenoid, I think is what it is called.





This sounds exactly like what my car is doing....."idling is really rough and unsteady (speeding up and slowing down)"

I have no idea what components your vehicle has...none...so I am blind....and his vehicle is different from yours, this I know....so, the following may/may_not apply

The computer attempts to control idle RPM....if someone has taken the adjustments out of specs, the computer may be oscillating.

Variation in speed also suggests extra air....does your vehicle have an EGR valve...if so, clean it out, and see if any vacuum is going to it at an idle. Take off the vacuum line, and plug it...for a test.

When the timing is done, is there an electrical plug on the distributor that has to be disconnected before checking this vehicle's timing at an idle?

[85_Ciera_Rebuild]

bottle of STP gas treatment into the tank (it says it removes water)


If your local stations are peddling E10....I don't think you need a gas treatment for water...it will suck it up too...I understand.

I'll get the name of that $6.00 stuff...it worked wonders on a VW with Bosch CIS system.

[Tuddi]

No EGR valve, no Oxygen sensor, no CAT, no plug on the distributor that can be removed without the engine stalling immediately.... but I DO have some strange equipment against the firewall on the passenger side:



At first I thought this was without any function... looks like some bad aftermarket addon for whatever purpose.

I flipped the switch earlier, and nothing happened. Then I flipped it 3 times in a row, and the engine stalled.

I started the car again, flipped the switch 3 times again... and the engine stalled. Repeated it one more time to make sure it was not a weird coincidence, and yes, the engine stalled again.

Position one for the switch is for normal, and position two is for adjusting timing (written in spanish). The valve in the picture was of course not connected to anything, but I put a hose on it and it is connected to the vaacum system now.

This is seemingly to be used when ajusting the timing... never seen anything like it before.

The carb in the car was from a Toyota 4 banger when I first got it, but I changed it for a Rochester Varajet II (refurbished). I don't know if the electrical choke is working or not (not that I need a choke in the climate here... but...) and the single vaacum brake on the carb is dead and disconnected due to there being a hole in the membrane and it doesn't hold any pressure at all.

You are right about me and John B having different cars, but the problem sounds very similar. To make a simplified comparison: If a 12 cylindered towing truck runs out of fuel, it will have a problem very similar to a 4 cyl granny vehicle that has ran out of gas. The symptoms will be very similarly described, even though there's a whole world between the two engines in question.

You mention the possibilty of the engine getting false air, and therefore causing varying speeds at idle. Yes that is also something one should consider as a real possibility. The air mix screw on the Varajet comes fixed from the factory, and should not be played around with..... but someone forgot to tell Peruvian automechanics that little detail The one in my carb has been violated with a welding torch and extended an inch or so with another bolt, and it is not fitting as it should (rattles... I will try to put a thread locker on it and hope it seals the threads from taking in false air... or find a screw that fits perfectly in there. I doubt it getting air through the threads, because if it did, it should constantly have the extra air (I have held the loose screw to one side in the threads checking if it would affect the irregular running of the engine, but it changed nothing).

All vaacum hoses are new and there are no leaks anywhere... as far as I have been able to determine. I had the PCV valve on the valve cover changed with a new one. The old one was at least a decade past bed-time.

Hopefully some day I will figure out what the problem with the idle running is. It used to be better, but went bad after I had the heads off to change the head gaskets. It has a bit of knocking going on under both covers. I'll also have to fix that... maybe it'is the real reason for the irregularity in idling?

[notsoslimshady76]

John: I've never had an ongoing idle issue related to bad gas. I really think its either a plugs/wire thing, or injectors. Try the fuel filter if you'd like to brave it. It really isn't too bad

[85_Ciera_Rebuild]

distributor


Got a pic?

[85_Ciera_Rebuild]

Try the fuel filter if you'd like to brave it. It really isn't too bad

Yes...but if we knew the fuel pressure readings....it can rule out fuel filter if pressures are within tolerance.

[Tuddi]

Distributor pics....

Top view:



Side view:



Plug cover view:



Inside view:

[85_Ciera_Rebuild]

Distributor pics....



See this thread: HEI: 2.8 V6: idling is really rough and unsteady (http://www.a-body.net/forums/showthread.php?p=3893#post3893)

[John B.]

The fuel filter is the first thing that was replaced on my car. It made no difference. I've had fuel filters clog up on other cars and it would cause the engine to miss at high rpm or other times when the engine needed maximum fuel but it would idle fine and run fine at low speeds. My car is doing something completely different. It's not idling right and misses under light throttle, but yet it can fly up the steepest grade at full throttle without any trouble at all. Anyway, I really thought we were on to something with the Bosch plugs, but why is it now suddenly running a whole lot better?

[85_Ciera_Rebuild]

It's not idling right and misses under light throttle, but yet it can fly up the steepest grade at full throttle without any trouble at all.

I've used this stuff before on a Bosch CIS (Continuous Injection System)....it works...but its about $7.00 with tax.
..
...

...
..
Techron Concentrate Plus (http://www.chevron.com/products/ourfuels/prodserv/additives/tcp.aspx)



Techron: From Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Techron)

Techron, formerly known as techroline, is a patented additive developed by Chevron Products Company, consisting of a family of compounds known as polyether amines.[1] Techron reduces accumulation of deposits in fuel injectors and on intake valves, and prevents or removes sulfur deposits from fuel sending units. With the introduction of Techron, Chevron gasolines became the first fuels designated as meeting TOP TIER standards for fuel cleanliness

[John B.]

I found that the engine wasn't idling right because of a massive vacuum leak. I don't think this is related to the initial problems of bucking/jerking/missing, but if it helps that problem too I'll let you guys know.

[Jr's3800]

A Massive Vac leak on an MAF equipped car can cause a lot of driveability issues..


Let us know if that solved the problem..

[85_Ciera_Rebuild]

I found that the engine wasn't idling right because of a massive vacuum leak.

Where?

I noted in post twelve that those symptoms cited represented classic symptoms of a Lean Mixture.

[John B.]

On the top driver's side of the engine is a rubber plug with 2 hoses coming out, 1 going frontwards and 1 going backwards. The one going backwards came completely off. But, this only happened a few days ago. The question is....before it broke completely off, was it cracked and leaking just slightly? I'm going to be replacing that part this week.

[notsoslimshady76]

It could have been cracked and just leaking. Those plastic hoses get brittle with age

[85_Ciera_Rebuild]

On the top driver's side of the engine

Just a tidbits summary:

When you have a drive-ability issue:

1. Code Check
2. Check Fuel Pressures specs
3. Use ether starting spray, and focus upon intake side with it
4. Check system components...wiring...

Rule Number One - Don't assume it is broke cause the Code says so...verify.

It took me two years to find a problem on a small block chevy....two long years....EGR Code was lighting up....and actual problem was never considered via GM manuals...the electric choke was still working, but not enough to fully open choke in cooler weather....this "poisoned" O2 sensor, so when computer checked EGR circuit, there was not enough change in O2 sensor reading, so the code lit up. With warmer weather, the choke would fully open (due to summer heat), but in cold winter conditions is when I figured it out since choke remained partially closed.

Not all problems are like this...but don't toss money at a problem cause the code points to a component.

[John B.]

Just wanted to update you guys that helped me out with this. Last week I had the plugs changed and the car has run PERFECT since then. It starts quicker, idles smooth, and does not miss, buck, jerk. Thanks everyone for all the insight and advice!

[85_Ciera_Rebuild]

does not miss, buck, jerk.

What's the plug gap, on the old plugs....070 or more?

[Jr's3800]

Not sure he would have even been able to read the gap on the Bosch Plats as the GM DIS system tends to erode the electrode into the Porcelain tip..

Glad to hear the car is running good.. With all of the Vac leaks solved and a decent set of plugs the 3100 should run really good:)

[Buick_powa]

Bad plugs can kill a car in a second! thats amazing!

[John B.]

My mechanic changed the plugs so I don't have the old ones. It is a difference of night and day though.

[jad1261]

I've been reading your posts and have not seen any suggestions about checking each individual coil for resistance values. I worked for the local Buick dealer 21 years and saw many drivability issues with these engines. The leading causes were plugged injectors,hi-resistance coils,non gm wires and plugs and on occasion an intake/vacuum leak at one cylinder. In 1996, GM as well as most manufacturers went to OBD 2 which would give a misfire graph on the scanner. This was a big help as a slightly plugged injector (#1 cause of most repairs that I made) would cause a service light with a powertrain dtc P0300. However in 1995 very few cars had this capability. Obviously a cracked insulator or pinched plug wire would be something to look for. A good way to look for this is to have someone else in the car with it in gear (aimed away from you and all other objects) and use a spray bottle with water while engine under load and watch for miss to get worse. Hope some of this helps---