96 Tahoe dies when warmed up

[WayfaringStranger]

What tool are you using to read the codes? Is that tool capable of reading cylinder-specific misfire codes? Or does it lie about cylinder-specific misfires by telling you they're "random" misfires?


The switch from open-loop to closed-loop operation shouldn't take ten or fifteen minutes.

Wild Guess: an electrical or electronic component is failing when it's fully warmed-up. I'd be testing the ignition coil for spark using a spark-tester calibrated for HEI, when the truck is hot enough to act up.

You may have a failed ignition coil, or ignition module that only causes problems when it's been run long enough to fully warm up. Similarly, the ECM could be screwy when fully warm, or you may have injector(s) that cause problems when the solenoid coils get hot.

Thanks, the code reader has read cylinder specific misfires on other vehicles before. I’ll look into the ignition coil

 

[WayfaringStranger]

In my experience, dies when warmed up is usually a large vacuum leak. The fuel enrichment when the engine is cold hides the leak, but once it's warm it quits enriching the mixture. Check very thoroughly for vacuum leaks before changing any parts.

Thanks, I’ll check for vacuum leaks tonight

 

[WayfaringStranger]

*Update*
I searched for vacuum leaks and found a hose completely missing. Amazed that it was running fine for so long. Ran a hose from point A to point B and fired her up. It’s running better but still bogs down and dies when warm. Now the only code it’s throwing is multiple/random cylinder misfires detected (although I wonder if I ran it for longer if I would get the “too rich” code again). I don’t have a lot of time to work on it but will check on some of your suggestions tomorrow. Thanks!
Incidentally can someone tell me what the missing hose was missing from? Thanks again

 

[kennythewelder]

*Update*
I searched for vacuum leaks and found a hose completely missing. Amazed that it was running fine for so long. Ran a hose from point A to point B and fired her up. It’s running better but still bogs down and dies when warm. Now the only code it’s throwing is multiple/random cylinder misfires detected (although I wonder if I ran it for longer if I would get the “too rich” code again). I don’t have a lot of time to work on it but will check on some of your suggestions tomorrow. Thanks!
Incidentally can someone tell me what the missing hose was missing from? Thanks again

I can't make out what or where the bottom pic is. The top pic is the vent for the gas tank EVAP system. There is nothing that is supposed to be hooked up to that line. It is a vent to pull the gasoline fumes out of the gas tank. That is where excess gas fumes vent.

 

[Erik the Awful]

I think OP stated his truck is running rich.

Doh! I missed that, but fortunately I was partially right. Not sure what that hose goes to, and I don't have a Vortec any more.

Misfires when hot? Next I'd check the ignition module for thermal conductive paste. If it has paste, try swapping with a known good module.

 

[GoToGuy]

The vac lines are diagramed in the service manual. And locations of all items. Don't guess, look it up, it will save headaches later. Is it original poppet injection or upgraded replacement?