1990 Sierra Baffled

[tnewman1]

1990. Gmc. Sierra 1500. 350. 5.7 v8.

Idles great. Runs strong. Then cuts out like its starving for fuel.
So far I have:
Dropped tank and cleaned it.
New fuel filter.
New fuel pump.
New ECM.
New Map sensor.
New ignition control sensor.
Vacuum lines good.
No shorts in the wires that I can see.
Intermittently stops fuel delivery on acceleration.
Help!

 

[Schurkey]

1990. Gmc. Sierra 1500. 350. 5.7 v8.

Idles great. Runs strong. Then cuts out like its starving for fuel.

WHEN? What's the pattern?

Cuts out at a certain speed? Cuts out after a certain amount of time? Cuts out at a certain RPM? Cuts out going up a certain hill pulling a trailer? Something else? Some combination?

 

[WICruiser-97]

Look at the circuits that shut off the fuel pump. There was a debate here about if the oil pressure circuit can cut off power to the fuel pump relay (I think the answer was no but...). The ECM uses a variety of signals to confirm the engine is running, crank position sensor primarily I believe. Check the wiring for the ciruits involved for indication of trama that would potentially result in intermintant shorts or breaks in the signal.

 

[tnewman1]

WHEN? What's the pattern?

Cuts out at a certain speed? Cuts out after a certain amount of time? Cuts out at a certain RPM? Cuts out going up a certain hill pulling a trailer? Something else? Some combination?

Thanks for your reply. Seems to start happening after its warmed up. Happens upon pressing accelerator about 1/3. Seems to occur on hills or flat. Shut it off and restart it, seems to run okay for a couple minutes then cuts out. Idles great. And runs strong when running. Hope this helps.

 

[tnewman1]

Look at the circuits that shut off the fuel pump. There was a debate here about if the oil pressure circuit can cut off power to the fuel pump relay (I think the answer was no but...). The ECM uses a variety of signals to confirm the engine is running, crank position sensor primarily I believe. Check the wiring for the ciruits involved for indication of trama that would potentially result in intermintant shorts or breaks in the signal.

I don't see any wire trauma but not sure what might be in the wiring harness.

 

[tnewman1]

Not surebif this helps, but when it cuts out, I put it in neutral, turn it off, turn back on, and put it in gear, strong as ever. Then a minute later, starts up again.

 

[Schurkey]

So it has problems, potentially during the switch from open-loop to closed-loop?

Connect a scan tool and verify EVERY sensor and computer output.

Connect a fuel pressure gauge to see if fuel pressure loss happens before or after the stall.

there was a debate here about if the oil pressure circuit can cut off power to the fuel pump relay (I think the answer was no but...).

"No" is the correct answer. The fuel pump relay can turn the pump on and keep it running. The oil pressure switch can turn the pump on and keep it running. Neither one can shut the pump off if the other one is keeping it running.