Help! 1991 Suburban cuts out suddenly, immediately restarts. Tried everything.

[MartinWD]

My mechanic (40 years experience) has tried and tried for weeks to find the reason my 1991 Suburban (350) suddenly cuts out but restarts immediately,

Replaced,

1. Distributor
2. Fuel pump
3. Fuel Relay
4. Ground wire
5. Computer (with the Prom)
6. Ignition switch
and more....

 

[Edelbrock]

So far here is what we know:

- Engine stalls.
- Engine restarts easily.

Recommendation -

1) Stop replacing parts.

2) Need more info.

Starts and then dies right away every time?
Starts and runs until its warm and then dies?
Starts and then dies randomly?
Starts and runs fine and then dies when you see a McDonals sign in the distance?


Need way more info on the symptoms.

 

[MartinWD]

It runs and then suddenly dies, but restarts immediately. Hot, cold, same thing. Randomly. My mechanic will let it sit and run and then it just dies. I drove it to his shop and on the way it was cutting out.

 

[1STLS1]

Electrical issues tend to be it works or it doesn't. Fuel issues tend to give a drivability issue prior to shutting off. If you don't have any codes to work off of, the next thing I would do is a harness shake test while its idling and see if you can locate a broken wire in the harness, last resort, meter each wire to the engine as you shake it. Sometimes it comes down to that.

Did you replace the distributor and ECM with new or quality reman or used?

When the issue is a "needle in a haystack", all you can do is keep making the haystack smaller

 

[gmbellew]

sounds electrical and something in the ignition system or computer controls.

has it ever popped either of the ECM fuses or set the service engine light? are the ICM wires in good condition, loomed, and not touching plug wires?

 

[Sad Sack]

One thing that I know that can this symptom, may not be your issue though, but idle air control valves can cause the random stalls. Vehicles with CELs will not throw a code which makes them difficult to troubleshoot.

 

[Edelbrock]

As others have said, its probably electrical and not fuel related.

As for the shake test mentioned above, I recommend using bumpy train track crossings or speed bumps. Just beat the hell out of the suspension, shaking the rig as much as possible. If its a broken or shorted wire, hopefully this will either fix the problem or stop the truck from running all together. Short the wire completely or bounce it away from the metal that grounding it out. The problem with this issue is that you cant fix whats not broken. So when its running, there is nothing to diagnose. When it stalls, you can't test anything because it just starts right up.


Out of curiosity, much have you spend on this issue so far for diagnostics and replacement parts?

 

[Edelbrock]

You may want to create a new account on this site and then send the credentials and a link to this page to your mechanic. It would be helpful to chat directly with the guy that's turning the wrenches. Of course you would want to stay involved in the conversation - not trading one person out for another, just adding another voice to the conversation.

 

[fast 99]

Check alternator, both AC and DC. AC reading near .10 [one tenth] justifies further testing of alternator. High AC isn't all that common. However, very easy to check with a digital volt meter and will cause all sorts of odd driveability problems.

 

[Ricko1966]

Get 5 foot of speaker wire and a 194 bulb. Attach 2 speaker wire leads to the 194 bulb,it's very easy a 194 has wire loops at the bottom you can attach to. Hook 1 speaker wire to a tee pin or a safety pin,put an alligator clip on the other. Now you can back probe the pin to the back side of the ignition lead at the distributor,clip the alligator clip to a ground. Tape the 194 bulb to the windshield,go for a drive. Is the light on when it dies? Yes move the engine side wires to the fuel pump relay out,and clip to ground again. Is the light on when it dies? Yes Next check for power loss to ECM check for power loss to injector. Then signal loss to injector. But the remote test light is your friend. First though as @fast 99 said check the alternator for A/C ripple it's so easy to test but creates crazy problems.

 

[Edelbrock]

Another test to see if the alternator is the problem:

Disconnect it.

Just drive straight off the battery (for testing purposes only, not full time). Do the problems suddenly go away?


Note: Might want to toss a fully charged spare battery in the back of the rig, just in case you run the "current" battery dead during the test drive.

 

[MartinWD]

Check alternator, both AC and DC. AC reading near .10 [one tenth] justifies further testing of alternator. High AC isn't all that common. However, very easy to check with a digital volt meter and will cause all sorts of odd driveability problems.

How would the alternator cause this?

 

[MartinWD]

One thing that I know that can this symptom, may not be your issue though, but idle air control valves can cause the random stalls. Vehicles with CELs will not throw a code which makes them difficult to troubleshoot.

Even when driving?

 

[MartinWD]

Electrical issues tend to be it works or it doesn't. Fuel issues tend to give a drivability issue prior to shutting off. If you don't have any codes to work off of, the next thing I would do is a harness shake test while its idling and see if you can locate a broken wire in the harness, last resort, meter each wire to the engine as you shake it. Sometimes it comes down to that.

Did you replace the distributor and ECM with new or quality reman or used?

When the issue is a "needle in a haystack", all you can do is keep making the haystack smaller

replaced the distributor with a new unit and then another from a known working vehicle. Bought a used ECM.

 

[MartinWD]

sounds electrical and something in the ignition system or computer controls.

has it ever popped either of the ECM fuses or set the service engine light? are the ICM wires in good condition, loomed, and not touching plug wires?

new plugs, plug wires, distributor, battery, alternator....