California Burb

OK I need help. The problem is beyond my ability and the ability of 3 different mechanics. Hope you guys can help.

I have a 1993 K2500 Suburban 4x4, 7.4L 454. About 160k miles.

Truck has run strong for years, and I maintain it and repair it regularly. I do a lot of the basic work myself (brakes, water pump, hoses, belt, oil changes), so I'm pretty familiar with it. It's been doing great until last week.

Truck suddenly died while driving on city streets. Sputtered and died. Put it in neutral and got it restarted, drove it another 100 feet and it stalled again. Managed to drift into a parking space.

Truck would restart but then die again within 30 seconds. Sounded like it had run out of gas.

* Changed the fuel relay - no change so I had it towed to my favorite mechanic.

* Mechanic said fuel pump - did that, no change

* Mechanic said ignition module, so changed that.

After all that, car was running, but running rough. RPMs bouncing all over the place -- +/- 1000 RPMs when driving. Really rough sound. Thought it might stall out again, but it did not. Seemed to get worse the more I drove. When I pulled away from the mechanic, it was fine. By the time I got home it was bad.


*2nd mechanic said that the new ignition module was bad, replaced it with a high-end part.
Truck ran fine in idle, no more stalling and RPMs were more quiet but still a little rough. Still jumping RPMs when driving but +/-200 instead of +/-1000.

I was not happy with this fix - truck was still far from 100%. RPMs jumping.

*3rd mechanic said bad distributor so after a lot of debate, I had him replace that.


Now my truck is driving a little better, but still jumping RPMs when driving and a bad sound like it MIGHT stall out. At idle it runs ok with the RPM needle bouncing a little.

Sounds like it is occasionally starved for air or fuel or spark. Like it's 'missing' every now and then (every few seconds). Acceleration is rough with the RPM needle bouncing its way up instead of smooth climb.

The truck does NOT sound right or run right. Way different than it ran just last week before all this.

So still no fix after:
- new fuel pump relay
- new fuel pump
- new distributor
- new ignition control module


They say they have checked:
- fuel pressure
- engine compression
- fuel injectors
- spark

Also:
- battery is 2 years old
- starter is about a year old
- fuel filter is 6 months old and was just checked again
- new water pump 3 months ago


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I noticed voltmeter needle jumping really bad when car first stalled.

Right now it seems stable, but voltmeter needle jumps a little when turn signals are on.

Voltmeter sits around 14, but inconsistent. Sometimes lower. Headlights don't seem to dim or change.


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One other problem (maybe related?) -- I have a small exhaust leak from loose exhaust manifold on driver's side. Was fixed a few months ago, but leak started back up. Manifold is a bit warped and a bolt is broken. I need to fix it. Makes a spitting noise when accelerating and I noticed some lack of power. Not sure if somehow related, mechanics think not.

********

Please give me your ideas. I'm all out of my own ideas, and I've spent over $500 on fixes in the past week and have not really gotten anywhere (except the car now idles OK without shutting off).


Thanks very much.

oilcanhenry

Might be you MAP sensor.