Help me diagnose please (Page 2/2)
olejoedad APR 29, 10:03 AM

quote
Originally posted by shemdogg:

If you can keep it running w shots of starter fluid, its a fuel issue. Fuel pumps wired thru the oil pressure sensor, if its going out itll stop the fuel pump.

shem



Sorry shem, not true.

The circuit through the OPS is a backup power circuit. The Fuel Pump Relay and the OPS both supply power to the fuel pump.

Why, you may ask?
That way, if the FPR goes bad, the car will start and run when the OPS sees oil pressure, preventing being stranded....

The OPS will NOT kill power to the fuel pump if it fails.

[This message has been edited by olejoedad (edited 04-29-2023).]

Raydar APR 29, 12:06 PM
If you can get it to stay running long enough to get behind the car...
Listen to the exhaust. If the cat is clogged up, you will hear it. Or won't hear it, as the case may be. (It'll sound really quiet - almost strangled - if the cat is plugged.)

If you've got a fuel pressure gauge, there is a shrader valve on the fuel rail, on the "belt" end of the engine. You have to unscrew the little metal cap, to access it.
Your fuel pressure should be ~40 lbs. Or in that ballpark.
armos APR 30, 09:46 AM
I agree the mechanic doesn't sound reliable. He sounds like one of those guys who likes modern cars.
But if you want a way to test for a clog, and you can't get it to idle for Raydar's suggestion, then you can try removing the oxygen sensor. It will leave an opening in the exhaust that should help the engine to be able to run. It might be hard to remove though, depending on your tools and how rusted it is. It's easier to remove if you run the engine to warm it up but in this case you can't do that.

To test if it's fuel try adding starting fluid as shemdogg mentioned. If that helps it narrows it down to a fuel problem.
If that doesn't help it might be ignition related, bad sensors, or it could be a mechanical engine problem (unlikely).

Check your fuses. What comes to mind is the 2 injector fuses. Each of them powers 3 injectors, if one of them blows the engine can still run, but badly. Mine was driveable like this but some cars might not be.

When you turn on the key, the check engine light should come on, turn off for a split second, then turn back on and stay on. If it doesn't do that blink then the ECM isn't functioning.
When you turn on the key, listen for the 2 second prime of the fuel pump. After it stops, blip the key to Start for a short instant and release it. You should hear the fuel pump running for a couple seconds again each time you do this.

If you're still getting nowhere, you could try unplugging sensors 1 at a time and see if that helps it run. There are more accurate ways to test the sensors if you get to this point.
Since you have a spare ICM, which I hope you know to be working and not dead, try swapping it out. It's a guess but it's a common failure and easy to swap.

A laptop running WinALDL plugged into the diagnostic port would give a lot of information but I assume you don't have that. The mechanic probably doesn't have a scan tool for this era of GMs. If he did he wouldn't be afraid of it.

[This message has been edited by armos (edited 04-30-2023).]

Fluff MAY 01, 10:37 AM
Thanks for all the good suggestions. I will pursue every one of them. The car is being towed as we speak. I stalked my old mechanic until I found out where he works now. The car will end up there once I have narrowed it down.