[joey93turbo]

I have a problem with my 1990 Suburban. It has a newer 350 in it with 20k.

When I go to start it the thing starts up fine, no throttle needed or anything, just turn the key. It'll run like normal for 30-45 seconds then it just shuts off. Doesn't seem like it dies, but rather shuts off, as if you switched off the key. It leads me to believe it may be an electrical problem but I have no idea. When I start it up the check engine light doesn't come on, so I don't know if it's throwin a code or not.

Any suggestions?

 

[charlo]

Sounds like the fuel pump quits after it "primes" the engine. I might check the wire that tells the ECU when the motor is being cranked. Might run to the starter(does on mine). Can you hear the fuel pump? Have a friend lay under tank and listen for quiting before she dies.

Charlo

 

[Todd C]

Make sure all the ground wires between engine, frame, body and battery are all good and well connected. This may not have anything to do with your particular problem, but it happened to me and was very frustrating to diagnose.

 

[KWTMECH]

I agree with the fuel circuit, also check the oil pressure switlch. Is it full of oil? Low pressure can do the same thing.

 

[juniordawg]

Will it run if you hold the throttle part way open ? I'm assuming it's still fuel injected, it could be your IAC valve, Idle Air Control Valve. Located on the throttle body.
To do a quick test :
Remove your IAC valve, spray some PB blaster or similar solvent in the port, then disconnect your coil and plug the port with an inverted vacuum plug. Then crank the engine 5-10seconds.
Next remove the plug and spray component cleaner in the port and repeat a time or two.
Clean and replace valve and reconnect coil.
Restart engine and time how long it runs, if it runs longer than it did before then replace the IAC. You may have to start it more than once to get the solvent out of the port, two or three times is more than enough.

Once again this is only if the truck will run if you hold the throttle part way open.

Don't forget to check the engine harness ground at the thermostat housing, these are notorious for corroding off.

 

[Black Dog]

As KWTMECH says, if the oil pressure switch is not working, the truck will do exactly as you describe. The computer will shut off the fuel pump if it does not see the oil pressure switch within 30 seconds or so. The switch is in the side of the block above the oil filter.