04 Suburban 2500 stalling, stumbling, no codes... need help

[james07moore]

Running too rich causes high negative fuel trim corrections that can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective oxygen sensors, exhaust issues, coolant temp sensor problems.

[95z28man]

These are all good ideas I need to look at, wish I had a better way to determine which to start with. I did not test my fuel pressure personally the shop did. However I assume since it wasn't acting up the fuel pressure was probably fine anyways. Everything is factory, the MAF is a Delphi that was on it when I bought it. It physically appears good and clean and I cleaned it myself. I am hoping when I get under it I can find a crappy looking ground or wire that maybe just acts up when it get jostled the right way or when an accessory is operated that puts any additional load on the motor.

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[Injuneer]

But the question is, why does it all of a sudden go from fairly stable to the extreme fluctuations in the STFT's near the 3/4-point, which do start to pull the LTFT's down? There is no corresponding erratic fluctuations in MAF rate or in the throttle position (although it requires assumption about the time scales on the different charts). Whatever causes the sudden rich condition (unclear if it’s a true or false condition) is affecting both banks equally.

It does get difficult to correlate the cause and effect when the graphic presentation appears to have two different time scales - one scale for the fuel trims and another scale for everything else.

Is there any way to generate a data file that you could post?

[95z28man]

I can look into how to pull the files from the blue driver. They are saving to my phone but not playing for me. I sent them via gmail to myself and could not open them either. I'll work on that get back to you. I can verify the timing of the graphs to match up even though the scales are different. I arranged them that way so I could see all the data at the same time while driving without scrolling.

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[95z28man]

The attached pic is some of the grounds under the drivers door that go to the 4wd system and some fuel or engine system. Not 100% exactly which ones yet but people have reported these grounds causing all kinds of weird issues. I dont like the way these look so I will be removing them grinding to bare metal and replacing with good bolts and terminations then painting and clear coating them. The driver pre cat O2 looks brand new, the other 3 look much older and worn so they may be something to replace for peace of mind.

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[95z28man]

This weekend didn't go as planned and I wasn't able to clean the grounds or check plugs. I intend in doing that this weekend for sure. Anyways the truck has been running great since I posted this initially. A thought occured to me about when I filled my tank last time. This was a couple days after the PCM was replaced and everything seemed perfect. I went to the same Exxon station and filled up at the same pump I usually get. For some reason the pump overfilled the truck and did not click off like it always does. Is it at all possible that because of that, something just briefly stumbled around the corner like I talked about in my original post and caused similar symptoms to what I was having previously? Like I said it corrected itself almost immediately and did not act up the rest of the ride home. Maybe overflowed fuel got somewhere it wasn't supposed to? I have also noticed that after 130 miles of driving on this tank my fuel gauge is still reading full. So either this new PCM gave my burb incredible fuel mileage or something got stuck from that overflow. That would actually be awesome if my truck is in fact fixed and it was just a bad coincidence that the tank overflowed the first time I filled it since the repair. Keep in mind the entire fuel pump and sender assembly was replaced a few weeks ago.

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[Injuneer]

I have no idea what the charcoal canister/EVAP system looks like on the truck. But typically, overfilling the tank can cause liquid fuel to get into the EVAP canister. Then when the EVAP purge valve opens, instead of pulling a mix of air and fuel vapor from the canister into the intake, it can pull liquid fuel, or an excessive amount of fuel vapor. That would cause the engine to run rich, and cause the reaction shown for the STFT's. The purge valve is only opened during certain engine operating conditions. Based on data logs from our LT1’s it can be during periods of high engine loads.

[95z28man]

I'll do a little bit of research on it when I get a chance but that would be awesome if that pump caused the issue. Thanks for the input, now I have a good direction to look.

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[SSlowBoat]

my g8 was freaking out (ls3 car) throwing lean codes on both banks for no reason. thought vacuum leak, cracked manifold, failed injector, etc since o2's were switching albeit a slight bit slow (about as fast as an lt1 o2 switches). replaced them and all issues went away

[95z28man]

my g8 was freaking out (ls3 car) throwing lean codes on both banks for no reason. thought vacuum leak, cracked manifold, failed injector, etc since o2's were switching albeit a slight bit slow (about as fast as an lt1 o2 switches). replaced them and all issues went away

I hope the issue was with the fuel overflow but those O2s wont be on the truck too much longer anyway. I'm looking into some stainless headers and exhaust and will be replacing all of them when that time comes. Just don't want to dump money into the exhaust until I'm sure my issue is fixed.

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