I've got doug thorley tri-y headers, no cats, magnaflow x-pipe, dual aero trubine AT2525's, and 4" dynomax tips. After I got the truck back from the shop it idles very rough and knocks off every once and a while. I thought it could be spark plugs, so I checked them and they're fine, even checked codes and there was no misfire codes, but there is PCM 0054 (O2 sensor code). I know this code should be there because of the cat delete, but could that be the cause of my rough idle? I'm getting blackbear to retune it so I hope that'll fix it, but I thought that the lack of rear O2 sensors had no effect on the way the engine runs, maybe I might have broke one of the forward O2 sensors?

 

A retune should remedy this.

 

the downstream O2s are there only to make sure the cats are working properly, when the cats are not then it shows up as a deviation out of a specified range but only by a little bit and it happens over time.

when you deleted the cats its WAY out of range and happened instantly so it may be your PCM freaking out thinking that something is WAY wrong. Im with him^^^ retune and that should do it.

 

Are you 100% sure that you have NO header leaks or leaks at the welds themselves? Alot of cheap headers have crappy welds at the collectors (usually in the center of the 4 into 1) which sucks air and throws off the o2 sensor into thinking it is getting more oxygen than it really is, so it increases injector pulse width to compensate fuel, which at idle you don't need. If you have a wideband o2, verify at idle that the a/f ratio is between 15.5:1 to 18:1 sitting below 800rpm's with a throttle load calculation under 20%- if its richer, this is exactly whats happening.

As for the rear o2's, it only tells the computer via difference of the front o2 readings if the cats are working. Unplugging or altering does nothing to affect fuel trim tables or any VE tables for the engine controls. If you can't just "delete" them or put the correct resistor in there to fool the ecm, go grab 2 sparkplug anti-fowlers and drill one out and screw it onto your rear o2 sensor. Then screw the one you didn't drill onto the other and plug the whole thing into the exhaust pipe. It creates a "zone" that allows the o2 to think its sampling (and also heat up normally to function correctly) and will "defeat" the computer into thinking the catalytic converters are in the normal threshold. People have been doing this for years to beat emissions after deleting cats from the system.

 

When you change airflow your gonna have tuning issues..IT sounds like you need a retune but you can recheck the header bolts and check the headers for leaks..


Doug thorley isnt cheap there sammy boy...

 

the P0054 code is for the heater circuit for bank 1 sensor 2, the downstream O2 for the catalyst. this should not create a rough idle condition. make sure the upstream O2's are tight and plugged in securely (even though there should be a code set for and incorrect signl from either of those O2's). and like the others have said, make usre all the hardware is tight, bolts, clamps, everything. if outside air is getting in it would likely set a fuel trim code for a lean condition in one or both banks.

check the easy stuff first, if there are no problems, disconnect the battery, reconnect and start the truck but don't drive or hit the throttle. just let it idle for 15 minutes. that's not the full idle relearn procedure but it could help.

 

Thanks guys I'll try that stuff. I knew about the spacer trick but I just disconnected the rear O2 sensors, justin at blackbear said he could tune it so the computer wont care anymore. I'm fairly sure I dont have any leaks upstream of the sensors, the headers weren't cheapos and they had nice welds on them, ceramic coated too. I do have an exhaust leak between the x pipe and mufflers but that's way downstream of the sensors.

 

The last thing I'd be worrying about on a set of thorley headers would be craftsmanship. Get Justin to tune it. If there's something wrong, and you're doing a logged tune. He'll see it.