My friend just had a y-pipe installed and a magnaflow muffler on his 02 Silverado. Now his truck pops bad when he goes wide open throttle like the fuel is being killed to the motor. I think this may be a side effect of what I am about to tell you. When I scanned his truck, his Ltrims are all RED and on the gauge display his Ltrim gauge was completely red and not giving any reading at all. In the histogram, the pcm was adding like 18-20 of fuel. In the DTCs table I got an O2 error that said something about not enough activity or something...can't remember for sure. What do you guys think? Does it sound like bad O2s or an air leak or something? I have never seen this much RED when I looked at a scan. Thanks in advance.

 

Could be alot of things, Have you all took a look down there yet? Was everything was cool before? First thing that comes to my mind is... Major exhaust leak, Next would be a disconnected or poor connection of the 02... What was the exact code, P0134, P0154?

 

Change the O2s. When an O2 goes bad, the PCM with richen up the engine as a safety.

 

Yep, a bad o2 will put you in full-time open loop operation, but if in open loop there is no fuel trimming. Could very well be an exhaust leak letting fresh O2 get to the sensors.

 

I checked for air leak. Looked good. Wires weren't burnt. I think maybe the O2s were bad causing it to dump alot of fuel and that maybe fouled a plug causing the popping. He got some new O2s yesterday and I haven't had a chance to scan it again yet. It is still popping I know, but I think that is going to be an ignition problem. Only pops at WOT.