96 Tahoe dies when warmed up

[WayfaringStranger]

96 Tahoe sat for several years before I got it. Replaced fuel pump and filter and plugs and it was running fine for a couple months. Now it runs great when cold started but starts to bog down and eventually dies when it warms up. Will have to very lightly press the throttle to get it to go. Pushing down on the throttle makes it run worse. Will always restart and run okay for a minute or two before dying again. Thought it sounded like an EGR valve so I replaced it and didn’t help. It has codes for system too rich in banks 1 & 2 and random misfires. Any thoughts? Thanks!!

 

[HotWheelsBurban]

Throttle position sensor and/or idle air control valve may be worn out. I replaced both of these on my 99 Vortec Burb a couple years ago, for a similar problem.

 

[stutaeng]

Probably injectors stuck open flooding engine and causing it to big down and misfire?

 

[WayfaringStranger]

Throttle position sensor and/or idle air control valve may be worn out. I replaced both of these on my 99 Vortec Burb a couple years ago, for a similar problem.

Interesting, I will check these out, thanks! Did your suburban run okay when it was cold but then have problems when warmed up as well?

 

[WayfaringStranger]

Probably injectors stuck open flooding engine and causing it to big down and misfire?

I was thinking maybe the injectors were the problem, but would it make sense for them to work fine until up until the point the engine warmed up? Off a cold start it will run 100% fine for 10-15 min and then start having problems. Thanks!

 

[HotWheelsBurban]

Interesting, I will check these out, thanks! Did your suburban run okay when it was cold but then have problems when warmed up as well?

What mine was doing at first was being hard to start and stay running. Then the idle was fluctuating wildly. I wasn't on this forum yet, so I called a relative who's a retired mechanic. He suggested those parts; I did TPS first, it fixed the problem for a while, then replaced the IACV.
There's also a coolant temperature sensor in the front of the intake manifold, that one tells the PCM how to set the mixture. I have been having intermittent problems with this one, but have a workaround for when it acts up.
If the truck sits for several hours, sometimes the key needs to be held in ON for a few seconds before putting it to START. I attribute that to the fuel pressure regulator being a little weak,and losing some of its prime. The truck just turned 200K and all the fuel injection components are original.
The trouble with hard start or problems like you're having is there's so many different things to diagnose if you're not getting codes. My truck's starting issues traced back to the passlock system, eventually, but I replaced a bunch of original parts (that did need replacement) before I got there. Another thing is does it do the problem in open loop( before the computer starts controlling things) or in closed loop( after the computer/PCM takes over).
Hope this helps....

 

[stutaeng]

Yes. The ECU doesn't use information collected from O2s, fuel trims, etc. when the engine is cold and in "open loop." As it warms up it goes into "closed loop" and that's when it tries to maintain fuel management based on those parameters...

But you need to properly diagnose before starting to change parts at will. If you don't have the time, knowledge, or energy just take it to a trustworthy mechanic...at least for a diagnostics fee.

As they say: the hard part is not changing the parts, it's knowing what the hell to change!

 

[Erik the Awful]

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.

 

[Schurkey]

runs great when cold started but starts to bog down and eventually dies when it warms up... ... will always restart and run okay for a minute or two before dying again... ... It has codes for system too rich in banks 1 & 2 and random misfires.

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?

I was thinking maybe the injectors were the problem, but would it make sense for them to work fine until up until the point the engine warmed up? Off a cold start it will run 100% fine for 10-15 min and then start having problems.

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.

 

[stutaeng]

Vacuum leak would cause a lean condition, no? I think OP stated his truck is running rich.

Maybe a leaky FPR since both banks are running rich?