`90 G20 - baffling stall out

Victim: `90 G20 5.7 TBI

Symptom: Runs for approx 45 seconds then idle surges and dies. Will not restart unless key is turned completely off and then on again.

Quick details: No error codes are present. When the problem arose, I replaced the fuel pump, fuel filter, and electronic distributor control module (not the brain).

I've checked the TPS and seems to be within specs an no "dead spot" spikes. Fuel seems to be delivered all the way thru to stall.

I'm completely baffled at this point. Anyone ever had this trouble or heard of it?

Here's some more info....

Just tried a new brain box and symptom stays the same. Also tried the loose gas cap trick back when I started working on it. Checked the EGR valve, MAP, but no matter what idle I hold it at, it just surges once or twice and dies. Cold or hot...

Someone recently removed the Cat Converter and put in a cutout pipe and walker soundfx muffler. I've done header/dual exhaust conversions before on both chevy and ford (up to `94) and haven't had adverse affects. Could that be a culprit?

Any suggestions would be appreciated. I'm getting good spray out of the injectors... Could it be a fuel cutoff relay?

Guess I'll just carry the convo myself...

Checked engine compression and excellent for a `90. Replaced the oil pressure relay switch, temp switch, fuel pump relay switch, AND rebuilt the fuel pressure regulator. Same fraggin thing...

How about the fuel injector? Could it be going bad?

I think I've found the culprit...

Underneath the seat, just beyond where the ecu (brain) is located (MarkIII 20 series), there is a connector that goes to what I just found out is called a "Fuel Pump recirculation control" circuit. Turns out, it is inline with the ECU (brain). While crude, here's how I figured it out:

First pulled the lil circuit board out and tried to start the engine. - Nothing.....

Second, put the board back in and started it. Listened to the stall out intently.

Third, restarted the engine and pulled the board immediately. - The engine stalled in the same exact manner as if I had left it in.

After trying that several times, I grabbed the lil board with bare fingers and got burned pretty good. That pretty much was the clincher.

Now, Even the Chevy dealer parts guy was stumped until he was able to find a superceded number for the original OEM number. I ordered one and expect it in tomorrow.

I'll post the actual name and Chevy replacement number for those that may be curious and whom may ever have this situation. I searched the heck out of the forums and found quite a few had this problem but no one ever posted their actual solutions.

After a barrage of explatives and a religious dose of one fingered gestures, I finally tracked down the culprit of the trouble.

The rear of the fuse block sits just above the where the battery is located. The wires that go into the rear of the fuse block are tight behind the battery and over the years of use (bumps,rattles,etc...) the battery literally beat the orange 12v feed wire enough to break it off inside its insulation. Thus causing the fuel pump relay and oil pressure hot feed to become dead.

The fuel module (5.7L & 7.4L engines) is what threw me off. It overides the 2 second ECM fuel pump "prime" by running the fuel pump for 20 seconds then shutting off. The ecm will recognize the distributor ignition module reference pulse and run for the duration of the fuel module's 20 second run time. You can turn the key and start it ten seconds later and it'll run only the remaining ten seconds.. With me so far???

Unplugging the fuel module will result in the default 2 second run time until the ecm gets the ignition module pulse and takes over its internal fuel pump drive relay.

Now, the problem lies in that there's a 12v feed that powers both the fuel pump relay AND the oil pressure switch. Your fuel pump relay is the main switch for the fuel pump. If it fails, the oil pressure switch takes over and will keep the circuit alive unless your oil pressure drops below 4 psi.

If that 12v feed is interrupted, both the relay and the oil pressure switch become dead on one side. Meaning the fuel pump won't even run on the 2 second ecm "prime".......

So, if any of you ever wind up having your G20 or hd truck start then stall out, and exhausted all other usual problems, make a jumper wire and connect it to the positive side of your battery and then to the ORANGE wire right at the Fuel pump relay connector. Then try starting the vehicle. If it runs for more than 20 seconds.. You've found the problem child!