My STE stranded me!

[73blazer]

I was driving down the freeway in my '89 STE AWD with 3.1l and it did an instant 1/2s cut out, almost like you got a sudden gust of wind like coming around a big truck on a windy day or something. Didn't think too much of it until it did it again 10 miles later then it started doing it constantly and I was losing speed and couldn't accelerate. I managed to get to the next exit and shut it off. It would restart and I could rev it for a few seconds and then it would die instantly. After it cooled off it wouldn't restart at all.

2-3000kmi ago I just went thru the entire fuel system, Renu'd tank, new fuel filter, fuel pump, senders/pickup/socks/tank lines, sent the injectors off to Mr. Injector for refurbish and balancing. It was running great, no issues, good fuel economy and good power (for a stock 3.1 haha). It really didn't feel like ignition , it was an all or nothing thing and no running rough or backfiring or anything of that nature. It did this in neutral, gear, or park so I'm pretty sure not tranny related.

I'm gonna guess it's probably a failed fuel pump, even though it only has 2000mi on it.

But I'm wondering, I didn't replace the fuel regulator, are those problematic on these cars? Anything else fuel or electrical/ignition that may cause an all or nothing cut out like that? EGR? anything? I did do some obvious checks for broke/disconnected vacuum lines and wire harnesses and connectors, nothing there I could find.

I've not had a chance to diagnose it yet, but the first thing I'm gonna do though is put a gauge on the rail and see if I have any fuel pressure.

[Pontiac6ksteawd]

Fuel pressure running is where I would be looking. It almost sounds like either the oil pressure is dropping, which is cutting the fuel pump.. Or the fuel pump/strainer/filter is clogged.

[73blazer]

Fuel pump is wired through the oil pressure sender? Hmmmm...didn't think of that one. I looked at the guages while it was doing it and didn't notice a drop in pressure, but I was only glancing down, i see bars in the middle, it's good...... I wasn't really watching it. It won't run at all now.

[Pontiac6ksteawd]

Will it run if you spray starting fluid in the intake?

[Keiths1976]

If any cut out condition would check the wire that runs from the crankposition sensor to the ignition control module ,that wire runs along the heat of the engine an the insulation rubs off and exposes the wire to the block and cuts out ..

[86euro]

I hate the internet sometimes, lol. The low oil pressure cutting off the fuel pump thing is an old wives tale that has spread like wildfire across the internet.

Yes, the fuel pump is wired to an oil pressure switch, but study the diagram again because it actually does the exact opposite. In the event of a fuel pump relay failure, the oil pressure switch let's the car start. When the engine cranks over and builds oil pressure, the switch closes and bypasses the fuel pump relay. It's a fail-safe built in by GM to keep the car running, rather than shut it off. So if you ever have long crank times but the engine otherwise runs fine, a failed fuel pump relay is a likely cause.

If this site had a photo uploader, I'd post the diagram. It's literally sitting here next to me.

[Pontiac6ksteawd]

So you are saying that if he lost oil pressure, it would shut the engine off after the fuel pressure dropped. So its not a old wives tale, at least not for the way I was explaining it.

But you are correct, upon turning on the ignition, the fuel pump should have primed the system, and allowed for it to start.

Another realm of possibility is that he has a fuel injector that shorted out. Since these run on batch fire, it would take all the injectors out on the related bank to the shorted injector.

[tlc1976]

There is a fuel pump test connector at the wiring block at the drivers side end of the firewall. Should be a red wire just sticking out of the loom, with a female flat connector. You can jumper a wire from there to the positive terminal of the battery to force the fuel pump to run. You should be able to hear the pump(s) run in the tank. If the car runs, and quits when you disconnect the jumper, then it's something wrong in the fuel pump control system. I believe the STE has a more complex control system with 2 pumps because the tank is mostly split by the driveshaft.

[86euro]

So you are saying that if he lost oil pressure, it would shut the engine off after the fuel pressure dropped. So its not a old wives tale, at least not for the way I was explaining it.

But you are correct, upon turning on the ignition, the fuel pump should have primed the system, and allowed for it to start.

Another realm of possibility is that he has a fuel injector that shorted out. Since these run on batch fire, it would take all the injectors out on the related bank to the shorted injector.

No, I'm saying that the oil pressure switch does not cut power to the fuel pump. It only supplies power to the fuel pump when the pump relay fails to do so.

Even without fully understanding the diagrams and how GM set it up, my wife has proven more than once that the fuel pump will continue running even when the engine has no oil pressure.

Oh, and my brother has proven that too, lol.

[86euro]

A fuel pressure test really needs done though, otherwise it's all speculation. If there is fuel pressure, then obviously check for spark. If no spark, check the two wires that Keith suggested first.

[CorvairGeek]

No, I'm saying that the oil pressure switch does not cut power to the fuel pump. It only supplies power to the fuel pump when the pump relay fails to do so.

Even without fully understanding the diagrams and how GM set it up, my wife has proven more than once that the fuel pump will continue running even when the engine has no oil pressure.

Oh, and my brother has proven that too, lol.

+1

The ECM will happily keep the engine running until it locks up without oil pressure.

I can only guess the misconception of the GM oil pressure switch being a 'safety device' rather than a redundancy started from the Chevy Vega (non-Cosworth) experience. The electric fuel pump was turned on and off by oil pressure only. With a small oil capacity and a thirst for oil, the engine would only run until the carburetor bowl emptied if it lost oil pressure. You could start the car without oil pressure, as long as there was fuel in the bowl or you cranked the engine long enough, I'll guess the concept morphed on the 'interwebs' as folks looked at our later schematics, seeing feedback to the ECM from the fuel pump relay circuit on some vehicles. This was misunderstood as a low oil pressure feature, rather than only a check of the fuel pump relay operation, at least until OBD2.

I'm sure it could be argued that an an engine that immediately stalled, from a brief low oil pressure incident, would be a liability nightmare, in today's litigious society.

[73blazer]

There is a fuel pump test connector at the wiring block at the drivers side end of the firewall. Should be a red wire just sticking out of the loom, with a female flat connector. You can jumper a wire from there to the positive terminal of the battery to force the fuel pump to run. You should be able to hear the pump(s) run in the tank. If the car runs, and quits when you disconnect the jumper, then it's something wrong in the fuel pump control system. I believe the STE has a more complex control system with 2 pumps because the tank is mostly split by the driveshaft.

I've always wondered what that wire was for! That would have been good to know on the side of the road, one jumper wire might have gotten me going again, if the problem is with the control system.
The STE AWD still only has one pump, it does have dual wells, it has some goofy forced suction off the return line feed from the R to L well. The return dumps into the R Well with an opening at the bottom and continues via a line back to the L well. The fuel pump is in the R well. I replaced all that when I went thru the fuel system. (That was a problem when I first bought it, you'd get just below a half tank where the common area of the tank splits to the wells and the feed line from R to L was broken so you'd start to run out of gas at just below 1/2 tank after it sucked the L well dry .... unless you took a hard left which would manually transfer fuel from R to L...haha)

I'll be back from out of town on Sat and will attempt to diagnose this then.

[73blazer]

Well, I'm getting stumped here.
Not sure what's wrong with it.
I have the factory service manual for it with all the wiring diagrams and diag procedures.
ALDL shows no codes. Fan comes on and flashes code 12 with jumper in.
I have 42lbs pressure at the rail (jumpered from the "prime" connector or while cranking). it's not fuel pump or control
I have spark. I removed one set of wires from a coil pack at a time, crank, and see the jumper voltage between posts. Did that on all three coil packs. Removed a few plugs and tested them the old fashioned way (grounded), and could see the plugs firing. It's not spark or ignition control.
The book only has one item left, injector control. I did notice when I removed some plugs for the test above, it was after cranking it over a few times for various other tests, the plugs were bone dry, not a hint of fuel on them. Did the couple of weirdo tests the book describes, they involve removing the 4 way from the ecm to the injectors at the back of the block above the valve cover, and check for power, and ohm some out, all checked out. Book then says "replace ECM"
I'm having a tough time believing it's that.

To make matters worse, it did fire, one time during all those cranking tests for about 3 seconds ran perfectly and died. The rest of the time there's not a hint of anything even remotely close to one or any cylinders firing, nothing. Just cranking. I'm almost betting it's a loose ground somewhere? I dunno, I tried wiggling all kinds of wiring in various places while someone else was cranking to see if I could shake something loose, no joy there either.

[tlc1976]

Did you check the ECM connectors to see if they were loose? I've never had them loosen up but some of my books say to check that. I'd unplug them and reseat them, just to rule that out. Just a handful of screws to pop the glovebox out and get to the ECM.

Also as Pontiac6ksteawd said, try starting fluid in the intake. If it runs good and stops as the fluid burns out then you know you got a fuel delivery problem.

[73blazer]

I checked the ecm connectors.
Didnt think to try starting fluid. Haha. The basics elude me apparently.
I just tried it. It will start with starting fluid.