Running rich and out of options

1500lbsoffrenchfries · July 1, 2021

My 2009 5.3 GMT900 flex fuel LMG motor is running rich. Short term fuel trims are on average -12 or lower (don't have an average field on my scanner, but it's at best a -7, at worst a -17, and most often it's a double digit figure). I've tried a new MAP, new MAF, new plugs, new fuel rail sensor, and tested the fuel pump pressure. The pump kicks out about 60 psi on a cold start and holds steady at 43 psi. I have tried resetting data by unplugging the power to the ECM - which works considering long term trims reset. Someone mentioned resetting the TPS. Not sure how with an OBDLink scanner. Other than that, my idle holds at -5 short term trim until long term trims becomes -5, then itll hold closer to 0 short term idle trim. Anything other than an idle has a double digit long term trim in the negatives and anywhere from -7 to -17 short term trim. Alcohol content is at 6.9% which seems right. It runs decent when you reset the trims, then it loses a bunch of power after maybe a quarter mile and goes back to running like a dog at anything besides WOT. Please help I'm running out of options. It recently cut P0172 and P0175 codes on both banks. I installed a short ram Specter intake about a month or 2 ago, but the engine has been running poorly before that. It didn't throw codes before however. All vacuum tubes are secure and I did a brakekleen vacuum spray test and there aren't any leaks I could find.

Edited July 1, 2021 by 1500lbsoffrenchfries

diyer2 · July 2, 2021

02 sensor. I believe default is to run rich when they have a problem.

1500lbsoffrenchfries · July 2, 2021

I just changed plugs, and the motor was definitely running rich. 02s on both banks going bad too at that seems odd. I'm wondering if the intake offset the MAF

asilverblazer · July 2, 2021

My first doubt is not the O2 sensors, they are detecting a rich condition thus the P0172 and P0175. So why is the engine running rich; however I would certainly monitor their behavior an replace if suspect. (They control/monitor the Air/Fuel ratio in simple terms)

You've been into the air intake so I would double check all that first. Air filter type? Maybe an excessively oiled filter element like K&N has messed up the MAF sensor.

If memory serves, WOT ignores some sensor readings which leads me to believe a sensor fault such as MAF or O2.

1500lbsoffrenchfries · July 2, 2021

It's possible the O2s are both going up, but what caused that? What I do know is, I drove the truck about 20 or 30k miles after I bought it without codes. I installed the intake maybe a 1k or so ago at most, and it kicked out a rich code at which point I saw trims in the negatives. I think the Spectre intake might be the problem, but I have no reference and my old intake is broken, so can't slap it back on. I'm taking it to a Tuner to see what he finds. The filter isn't oiled I believe