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

[Edelbrock]

How would the alternator cause this?

If the alternator throws AC power (as opposed to DC) into your electronics or computer, it can basically cause the parts to have a seizure. Its like you getting hit by a taser while trying to draw a picture of a dog.

 

[fast 99]

How would the alternator cause this?

Excessive AC voltage "confuses" [for lack of a better term] overheats or overloads electrical devices. Like I said have seen it cause a multitude of odd electric issues.

Remember one vehicle, [Northstar Caddy] bight me real hard in the backside. I never checked the AC voltage until 2 days into chasing a horrible running engine. Disconnect alt motor ran like a champ.

Now I check it all the time. Not hard just attach a digital volt meter to battery posts, engine running. There will always be some AC just don't want a lot of it. Battery is a large capacitor. AC will be higher with a poor battery so I can't give you a hard number. Just that a .10v reading would peak my interest.

 

[Camar068]

Check the wires going to the distributor. I had a blue crimp connector on mine and it would lose connection there and there. If not applicable, carry on.

 

[MartinWD]

Even when driving?

yes

 

[MartinWD]

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?

probably around $1,500

 

[Edelbrock]

probably around $1,500

You may want to consider a different mechanic.

When someone brings a vehicle to me, I do the diagnostics for free. If I say that it needs a part, and replacing that part doesn't solve the problem - then there would not be any charge for any of the work. Why should they pay for a repair that's not a repair. Very rarely has this ever happened, but one time does come to mind (this happened about 10 years ago):

A car was not running very well, and had a camshaft position sensor code with the check engine light on.

So I replaced the camshaft position sensor. The code remained, and the car still ran bad. So there was no charge to the customer. I send her to a friend of mine that specializes in high end diagnostics. He used a big machine to detect the problem.

The little magnet on the camshaft sprocket had become weak, and somehow lost some of its magnetic ability, thus not triggering the camshaft position sensor properly. He had a readout on his computer that looked like an EKG, showing the performance of the magnet with each revolution of the cam.

Now she did need to pay him a fee for finding the problem, but he would not have charged anything if he had not found the issue.


After $1,500 - your still having the same issue.

I hope he put all those used parts in a bog box and gave them back to you. Otherwise he is getting paid more that the $1500. He is getting a bunch of known good parts as well.

 

[carnutjw]

I know this sounds very basic, but shortly after I bought it, my Suburban would intermittently shut off for half a second. The Holley Sniper readout and trailer brake screen would blink and the truck would stumble. After some poking around I found the HOT wire to the starter was loose at the starter. Tightened it and we're all good. The last guy to fool with it probably went finger tight and forgot to put a wrench on it. $0