random misfire bank 2 ONLY gas fouled plugs.

[geterdonejoe]

all new sensors. new motor and trans. new plugs, wires. the motor consistently misfires (after 45 seconds) and runs very rich on pass side only. here is the weird part, when I start the truck it runs fine for about 45 seconds then gradually begins to misfire and "load up" on the bank 2 cylinders only. another 30 seconds then the mil flashes and I shut it off. 150 lbs. across all 8. 50 lbs fuel pressure steady. new map new crank pos new cam pos new knock sensors and pigtail. new intake gaskets also. fuel pressure holds after shutoff so no stuck injectors. mass air sensor is next. could somebody please tell me why my truck is loading up on bank 2 only? this is my livelihood.  pull all plugs , driver side: perfect color. passenger side: thick soot deposits in very little time. swapped coil assemblies no change. HELP!!!             Follow up: sorry i should have given truck type and year. It is an 02 sierra. And you were correct it was a bad 02 sensor. I switched sides and the code popped up in the opposite bank. $80.00 later and i have been MIL FREE FOR 30 miles now and running tip top. Thank you !!!!

Edited June 15, 2022 by geterdonejoe

[Jsdirt]

Don't have any idea what you're working on here, but this is a classic symptom of a bad o2 sensor. When you first fire it up, it's running in open loop. When in open loop, NONE of the sensors are being used to calculate fueling requirements - it's all pre-programmed in the engine computer. Once things are warm enough, it switches to closed loop, which then uses ALL sensors to calculate fueling.

 

Should be throwing rich codes, and possibly o2 codes. Posting whatever codes it has would be super helpful, along with year, make, model.

 

Pretty simple to troubleshoot watching live data on a scan tool. If the upstream sensor isn't switching from rich to lean at a rapid pace, and is just hanging at a high voltage (.7v-.9v), you've got bad sensor wiring or a bad sensor. Unplugged the scan tool should show .450v - if it shows this, wiring integrity is good. 

 

Another possibility is a stuck open EVAP purge valve with a flooded charcoal canister (If filled to the brim, and you forced a few more "clicks" at the pump in there). Scan data and codes will tell the tale.

 

Just FYI, if this is a GM truck, 50 lbs. is on the low side. Should be 55 - 60 psi. This could just be a gauge variance, though. I would concentrate on the problem at hand first.