Hi there. So I've been trying to get this fixed for a while and I'm getting kinda stumped and almost wondering if the ECU is failing on our tahoe. I have a scan tool with the ability to reset the fuel alcohol content and fuel trims. Seems like this stupid car has to have the f/a content reset every couple weeks. We use just regular 87 pump gas never e85. Currently the long term fuel trims peg to -30 on both banks. Even after resetting F/A and fuel trims, fuel trims immediately jump to -30. We replaced the fuel injectors with new AC Delco fuel injectors 2 years ago. New air filter and a new maf. From what I can tell the sensors are reporting to the ECU correctly but the dang long term fuel trims are killing me. Any help or somewhere to start would be great.

 

I’ve been have the same issue as well still no fix yet.
what’s your alcohol percent reading?

have you tried the mass air flow sensor?
check for vacuum leaks as well.
I’ve done just about everything so far besides the o2 sensors.
waiting on a scanner to reset the trims and fuel alcohol percent and see if it helps then I’m going to try o2 sensors.

 

Yep brand new maf. Alcohol is currently reset to stock 3% or whatever it defaults to. I haven't gone with new o2 sensors yet. Sprayed carb cleaner around the whole intake and rpm never fluctuated

 

I feel like if it were the O2 sensors though wouldn't it kick a code for O2 sensors?

 

that’s what I thought would happen as well but from research the past few days people put some in and it fixed their issues.
I was going to start with the upstream since they’re the most important and then the down streams if it still don’t work.

 

Huh good to know. I hate the flex fuel and the AFM on these vehicles. Doesn't do any good just harm. Maybe I'll try replacing them. Haven't had them replaced in a long time and the Tahoe has almost 400,000 on it

 

my AFM has been disabled. Having it damaged the lifters in the long run.
mine has 198K right now.
i figured i would try o2’s that’s really the only thing left to try. The o2’s reads everything the emissions is doing and sends it the the computer to how much air to fuel it needs to run. My alcohol is at 63.9% I’m waiting on my scanner to arrive to reset it back to normal.