94 Yukon 350 Idle issues and Loss of power.

[Schurkey]

Truck started and ran until the scanner booted and shut off.

The truck stalled as soon as the scan tool booted? Related? Or coincidence?

I sprayed the TB with starting fluid and it didn't even try. Had my amazing and flexible wife replace the ICM for me. She noticed the screws on the cap only got finger tight and nothing more, just free spinning but cap was tight and not moving so we resumed. Same crank no start, but fuel pump relay code came up, I just so happened to have one and swapped it. No change. I am still at a loss.

Do you have spark? Have you checked with a spark tester calibrated for HEI at the end of two or three plug wires?

Do the injectors spray during cranking? Does the pump prime? If you crank long enough to build oil pressure, do the injectors spray? Do they even click during cranking?

 

[AllStrobedUp]

I think the scan tool is unrelated.

I do not have a spark tester.

I did not have the assistant of my wife so I can't see if I had Injectors firing.

It did not start with starting fluid.

It built 80psi of oil pressure.

 

[AllStrobedUp]

UPDATE

Huge thanks to @scott2093 we have been remotely and in person troubleshooting this truck for a few weeks now. He has lent me his hands, his parts, his scan tools and manuals and we have finally tracked it down.

It was the distributor pick-up. We swapped in a spare distributor which was timed perfectly I might add and she came right to life on the first bump of the key.

I have his backup in the truck and will be ordering a replacement.

 

[scott2093]

Do you have spark? Have you checked with a spark tester calibrated for HEI at the end of two or three plug wires?

He ordered one and it showed up a few days ago and that led us down the right path. The truck running sometimes was confusing. The spark tester wasn't tricked.Thanks ...Again

 

[Schurkey]

Spark testers are SO inexpensive, and SO useful that everyone with wrenches should have one.

 

[AllStrobedUp]

Okay, so everything is fixed, replacement distributor is in and working great, I have found that it runs best at 2° base timing. But, now that it is running so smooth and great at temp with the AC on in gear it idles at about 450-550 RPM which is below what my alternator charges at. I need it to idle at 650-700 to charge. Without taking the slug out of the TB and adjusting it how do I get the RPMs up about 100?

 

[Schurkey]

Determine what the factory wants the engine to idle at. Make sure that is the idle speed you're getting.

You can dick with the minimum idle speed screw, but then the IAC will just counteract what you're doing, and probably cause additional issues besides.

If the idle speed truly has to be corrected...you'll reprogram the computer to do it.

 

[tayto]

need PROM tuning
easiest would be get an alternator that charges at lower rpm

 

[AllStrobedUp]

need PROM tuning
easiest would be get an alternator that charges at lower rpm

That is not an option. I have a very nice and expensive 400A AutoTech Alternator. It's never been an issue until now and I think the truck idles too low anyway. It should be at the 600-700 range warm.

 

[Schurkey]

First Guess: 650--700 IN GEAR is too high.

Put a smaller pulley on the alternator. Hope you don't have problems when the trans kicks-down and engine RPM goes up.