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    Mass Air Flow (MAF) Sensor

    My 88 Beretta has been down for preventive maintence for about two weeks. After installing new timing set and water pump, I fired it up and let it run for several plus minutes while topping off anti-freeze. Then I went back to turn it off and noticed SES (Service Engine Soon) light was on hard....Code 33....MAF Sensor Circuit.

    Question - I'm going to check a few things Friday, but has anyone had this happen before where the vehicle sets for several weeks, and then the code is set?

    Shop Manual suggests prolong idling will set it, if other conditions exist ( TPS less than 8%, Air Flow greater than 20 grams per second).

    #2
    Does your manual indicate if this code means a total lack of continuity or just a reading outside spec?

    Comment


      #3
      Originally posted by CieraSL92 View Post
      Does your manual indicate if this code means a total lack of continuity or just a reading outside spec?

      1988 Beretta: 2.8 V6: Code 33 (too high frequency)

      Code 33 will set if:

      * Ignition "ON" and air flow exceeds 20gm/sec

      OR

      All of the below are met for 2 seconds:

      1. Engine is running less than 1300 RPM
      2. TPS is 8% or less
      3. Air flow greater than 20 grams per second
      &&&&&&&&&&END&&&&&&

      When I drained the radiator, I had to remove the battery and I opened up the Air Filter Container, which exposed the MAF to direct air for about two weeks.


      Code 33 (Too High Frequency) means that MAF is detecting a fast movement of air going across it....I'm going to have to see if I screwed the Air Filter Container down right...it was getting dark when I screwed it down...

      I'll know more Friday

      Comment


        #4
        I took it out for a Test-Drive...and with the pedal pressed, the SES Light goes away...but as soon as the pedal is released, the SES Light comes on.

        I have a digital mpg gauge, and it too follows SES Light...when light if off, fuel mpg goes back to normal...when SES Light stays on, fuel mpg sucks, at around 18 mpg.

        Something to do with TPS, in some manner...I don't know yet...have to get a reading on TPS sensor via relative of mine...bummer.

        Comment


          #5
          Update - I took it on a 160 mile cruise today...same symptoms, SES light goes off under throttle usage. I bought a can of MAF sensor cleaner...no cigars.

          M.P.G is about the same or better with this condition...maybe a pinch better...but I must assume computer is using O2 sensor to control fuel burn. I have digital display which has mpg displayed. Initially, mpg sucked, but with more miles, mpg went up...so, I must conclude O2 sensor was determining the fuel burn. (battery was disconnected for several weeks, so computer had to relearn via O2 sensor).

          Most likely, I will buy another MAF sensor....I have this feeling my fuel mpg will drop when I do.

          I was driving on interstate roadway and was getting about 35 mpg at 60 mph, with one heck of a wind behind my vehicle....cheatin...

          Comment


            #6
            I don't use a MAF. K&N cone filter straight to the throttle body. I've gotten 34 on the highway. Is your car updated with speed density? If so, ditch the maf.

            EDIT: Just realized the ecm probably wouldn't throw a maf code if it's running off the map...

            I actually remember having a tps voltage issue before, and the ses light was on w/no throttle, but went away w/throttle. But that voltage was tricky. Even if I adjusted it so the light was gone allt he time, the computer would behave wildly. For instance, when I had I believe .56v at no throttle, there was no ses light, but on startup the engine would idle very high. So high it sounded like it was towards the redline. Once it was put in drive though, it drove beautifully and idle was fine. Lockup would also immediately engage when the throttle didn't move for more than .3 seconds, no matter what. I actually liked how it ran with high voltage, all except for that obnoxiously high idle which is NOT a good thing for a car to do when it's just started up with the engine not fully lubed yet!
            Last edited by Tonglebeak; 12-02-2007, 04:59 AM.
            2004 Chevrolet Impala SS Indy


            1986 Chevrolet Camaro Z28 5.0V8

            Comment


              #7
              Start looking around in the junkyards for a 88 model Beretta, that has the speed density software installed. It will have a sticker saying this on one of the strut towers. If the motor and tranny are the same as your car, take the EEPROM out of the computer and try installing it in your car. If this clears the SES light, then you can remove the MAF sensor completely, and wire in a IAT sensor into the air canister. Your MPG will go up, and you will get a slight power increase. I did this on my 87 Pontiac 6000 LE, using a chip from a 88 Chevy Cavalier Z24 Automatic. Speedo stayed correct, no check engine light, and no more MAF. Fuel milage went up 3-4 MPG.

              Or you could go to the dealer and ask them how much the Speed Density software upgrade is. Might be easier than hunting down a speed density chip.
              Brian - Carpe Diem

              I dont have to love my president, or any god, to love my country!!
              More people have died in the name of "God" than in all wars combined thruout history
              01 Pontiac Aztek GT AWD 127k - 04 GMC Envoy SLT XUV 193k

              Comment


                #8
                Originally posted by Tonglebeak View Post
                I don't use a MAF...Is your car updated with speed density?
                ....remember having a tps voltage issue before, and the ses light was on w/no throttle, but went away w/throttle.
                After cleaning the MAF Sensor yesterday, I forgot to plug it back in....duh...and drove it some 120 miles.

                Today, I plugged it in, and these Extra Codes came up:

                23 - Manifold Air Temperature (MAT) Sensor Cirucit
                33 - Mass Air Flow (MAF) Sensor Circuit
                45 - Oxygen Sensor Circuit

                So, I just now unplugged the battery and MAF Sensor...maybe later today I will drive it to town.

                It worked fine without MAF (once 02 sensor had enough data points in computer).

                Speed Density Software - Yes it has it, I just now Googled it, and found this story:

                1988 Chevrolet 2.8 is a strange bird.


                They began manufacturing "speed density software" to update these vehicles. This speed density software consisted of a new prom, a new idle speed control motor, and a label to attach to the ECM (computer) that the vehicle had been updated with the speed density software. I am unsure of exactly what this corrected, but it told the ECM to ignore all signals from the MAF sensor. The MAF (mass air flow) sensor was still there, it just didn't do anything anymore. It presents problems for a repair technician if he is unaware of whether the vehicle has been updated or not. A scanner plugged into the ALDL link will give erroneous data and trouble codes if the vehicle has been updated and the scanner is not made aware of it!
                ...
                ...End...

                TPS Voltage:

                Even if I adjusted it so the light was gone allt he time, the computer would behave wildly.


                On cold startup...everything is fine....when motor is warmed up, then at startup, motor will go to about 2,000--3,000 RPM and come back to around 1,000 in neutral.

                I'll have to check voltage and see where TPS is now...everything was "normal" before I worked on it, but it got colder around here, and voltages change with colder air. I know someone has messed with this vehicle...so like the article says,

                Even the technicians at the large Chevrolet dealership near our shop tell us that they try to run from them (1988 Chevrolet Beretta with a 2.8 V-6 engine) whenever they come in.

                Comment


                  #9
                  The MAF has a built in IAT sensor. The computer should still be reading at least that much from the MAF, actually.

                  Also, for my car the speed density sticker is in the glovebox compartment, as well as a couple of other places.

                  But I recommending doing what I did, and that's ditching the MAF (ditch the entire air intake altogether if you can, at the least the ciera's had a huge bottleneck right from the beginning).

                  You will need an IAT sensor. As you know, all I did was get one of those intakes off ebay, which is just a short pipe with a k&n cone filter on it, and a hole to seat the IAT sensor. Splice it in and you're good to go (I believe it's the pink and brown wires. Don't quote me on that yet, I need to go doublecheck).
                  2004 Chevrolet Impala SS Indy


                  1986 Chevrolet Camaro Z28 5.0V8

                  Comment


                    #10
                    Originally posted by Pontiac6ksteawd View Post
                    Start looking around...has the speed density software installed....
                    According to this article I found, this mechanic notes:

                    ..Immediately, GM had some sort of problem with this arrangement. They began manufacturing "speed density software" to update these vehicles. This speed density software consisted of a new prom, a new idle speed control motor, and a label to attach to the ECM (computer) that the vehicle had been updated with the speed density software.


                    Hence, you would also need a revised idle speed control motor.

                    This vehicle has the speed density sticker on it...so I must assume it was upgraded.

                    thanks to both of you mentioning this....

                    Comment


                      #11
                      Originally posted by Tonglebeak View Post
                      EDIT: Just realized the ecm probably wouldn't throw a maf code if it's running off the map...
                      I would have to do a series of test since when I initially checked Code, it was after I did the repairs, and then just started the vehicle up to let it idle, and it threw a code....later I drove it around, but never checked it until some 150 miles later. So, different conditions...

                      Originally posted by Tonglebeak View Post
                      tps voltage issue before...
                      Vehicle's wiring shows TPS and MAF (temperature side of MAF) use the same ground path back to the comptuer...which means one needs to check all terminals first before messing with it.

                      Comment


                        #12
                        Hmm, I didn't think they did that. Hmm...

                        BTW, when you adjust the tps voltage, make sure it's at .5 volts.

                        And another thing: you can rest assured that even though everything else might be going wrong, YOUR ENGINE AND TRANNY IS FINE!
                        2004 Chevrolet Impala SS Indy


                        1986 Chevrolet Camaro Z28 5.0V8

                        Comment


                          #13
                          Originally posted by Tonglebeak View Post
                          BTW, when you adjust the tps voltage, make sure it's at .5 volts.
                          Have to get another manual for this matter: which I just bought.

                          1987-1988 GM-Wide Driveability and Emissions Diagnosis & Trouble-Code Manual for 2.8L VIN W Speed Density Engine #75841

                          GM's update, Speed Density Software, is what a person needs to know here first before messing with it.

                          Originally posted by Tonglebeak View Post
                          YOUR ENGINE AND TRANNY IS FINE!
                          Well, let's see, the previous owner was attempting to sell this vehicle to the Salvage Dealer, so I bought it for its transmission without seeing it for $200.00....hmmm....and now I've spent about $800.00 in parts (+ 2 tires...plus my cheap labor)....hmmm

                          But, since I checked a rod/main bearing for clearance, it should run another 100,000 miles...only need to change transmission's CV seals and maybe front wheel bearings now...then it should be a good ride without mechanical problems....

                          Comment


                            #14
                            I am unaware of a revised idle air control motor. It could be just a better "improved" design internally or it could have a different sized plunger which could help the computer adjust the idle a little quicker, maybe. Was it stated what was different about it?
                            -Andy

                            '86 Eurosport VR coupe
                            '86 Eurosport sedan
                            '88 Eurosport VR coupe
                            '89 Eurosport wagon

                            Comment


                              #15
                              Originally posted by 86euro View Post
                              Was it stated what was different about it (IAC)?
                              I'll come back to this topic when I receive the manual I ordered today....I'm sure all the details are spelled out in details there...

                              This mechanic seems to think so...

                              Comment

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