I have a 2003 2500HD 6.0 automatic non allison trans. I got exhaust put on at my local exhaust shop last saturday, the jackass who put a new cat on the truck a few years back shoved exhaust pipe inside the cat hitting the o2 sensor and damaging it instead of clamping it or welding it the right way. I got two new cats, pipe, and muffler from the cats back. The OBD2 showed codes for the o2 sensor downstream (which was the bad one) and cat codes. I cleared them on my tuner when I got home which was 5 minutes from the shop. I realized the truck was running a little rough since the hole for the o2 sensor was plugged until I could get one for half the price they wanted and I could put in myself. I had to order the sensor so it took a few days but it only took a day for the truck to run bad enough I didn't drive it for a week. I put the new sensor in, new plugs, and changed the oil yesterday, it still ran terrible. Today I bought new wires since the codes were still there, i also changed out coils 6 & 8 because my friends scanner said they were the two misfiring even after the new plugs and wires. Needless to say its still running bad and i put the tune I originally had back on and it runs better and it showed there were no misfires as it was running but o2 sensor codes for all 4 were showing and mass air code. I cleared the codes and drove it about 3 miles and plugged it back in after and all the codes were back AND about 4 cylinders were taking turns misfiring... Im so fed up with this damn thing and I work on cars for a living and so do my friends that helped me and were all stumped. Our next thought is to take the intake off and valve covers to make sure theres no internal damage from the backfiring. We also re-learned the crank position and it was successful but still no help. Someone PLEASE help with this, Im so frustrated and tired of spending money to rule things out even after testing them showed it should be done. I can't get on this forum too often so please email me with the subject "chevy forum help" my email in cjackman911@gmail.com. Thank you!

 

post all the codes that are setting.

 

Last Sunday I put the truck back to the stock tune (as per the tuner). I decided to put the tune on that I took off last Sunday to see if maybe the stock tune wasn't saved correctly to the tuner which was causing an issue. After I put the previous tune back on the truck last night, it started running better from 1/4 throttle and more. Low RPMs and idle it was choppy but once i got past 1/4 throttle it put me in the seat and ran like a raped ape. I checked and saw no misfires at that time, so I cleared the codes and drove it again. When I got back 10 minutes later, multiple cylinders were misfiring and these codes came back up.
P0101 Mass or Volume (mass air)
P0131 O2 Circuit Low Voltage
P0137 O2 Circuit Low Voltage
P0155 O2 Heater Circuit
P0157 O2 Circuit Low Voltage
P0300 Misfire.

One of the O2 sensors is brand new I just put in the other day along with the other list of stuff I previously said. This is driving me nuts and I haven't the slightest clue anymore of what it could possibly be. Any input would be greatly appreciated!

 

doubt its 02 sensors as they are ignored until closed loop operation. If it was a bad o2 the truck would run good in open loop then poor when in closed loop. you may have a bad 02 heater but that is not related to your problem.


What are the fuel trim values at during idle, at 2500rpm and during a hard acceleration if it will do that?


Look at things that would cause the fuel trim to go lean on both banks...low fuel pressure, bad maf and bad map.


What does the map read koeo? What is the barometric pressure where you live? Do the numbers match?

 

I don't remember the readings, Ill have to check them again when my buddy is available with his scanner. Im going to do an injector flush tomorrow at my work and put the other o2 in just cause Id rather have at least two new ones on the same bank anyway.