Truck will start up and idle great for a while then it just shuts off

BRCOPELAND

MEMBER
1991 CHEVROLET SILVERADO
4.3L
V6
2WD
MANUAL
175,000 MILES

Replaced ICM, pickup coil, rotor, distributor cap, wires, spark plugs, coil, fuel pump and sending unit and fuel filter. Truck will start up and idle great for a while. Then just quits running. When that happens it is extremely hard to start back up. I know the timing is off a little and will work on that this week. But I cannot for the life of me figure out what is making it do this. Please help before I pull out all my hair.

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Welcome to 2CarPros.

First, if you haven't already, pull diagnostic trouble codes that may help us narrow things down. Here is a link that shows how to do it on a GM OBD1 system. All you will need is a jumper wire or even a paper clip.

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Let me know if there are codes stored.

Also, keep in mind, the ECU monitors input from several different areas to determine spark timing. Here are a few of the things it uses.

The ignition system has a distributor module with four terminals for the EST system that are connected by the ECM.

To properly control ignition/combustion timing, the ECM needs to know the following:
Crankshaft position
Engine speed (rpm)
Engine load (manifold pressure or vacuum)
Atmospheric (barometric) pressure
Engine coolant temperature

I have seen the engine coolant temperature sensor cause the fuel mixture to be so far off that the engine will carry on and then stall. It's just food for thought at this time. Also, make sure the are no vacuum leaks that can cause issues as well.

Let me know what you find.

Joe