Ok. I apologize in advance about the amount of details. My 05 Ram 1500 5.7 threw a p0420 code so I decided that now would be a pretty good time to put some headers on it. I just installed a complete exhaust system. TTI headers, new cats, muffler, ect. The code went away for a few days, then it popped back up, but this time it was throwing codes for both banks. (p0420/p0430). I have access to computer diagnostic equipment so I was able to look at the graphs of the O2 sensors and when I looked at them, the upstream bank 1 graph looked the same as the downstream bank 2. So I was thinking that maybe it was the PCM crapping out on me or maybe its something simple like the O2 sensors.

Just looking for some input, because both my mechanics teacher who is ASE certified in all 50+ areas and I are completely out of ideas. My gas mileage has suffered tremendouslty and I need to figure something out soon. Any help is much appreciated.

 

Doubt it's the PCM if you are ONLY showing emissions CELs. Check your work around the exhaust manifolds for leaks.

Also, if you used high flow after-market cats, the stock sensors often have a problem with them. In combo with the headers your flow is actually too good and out of the "acceptable range" so you'll pop a CEL. There simply isn't the flow difference the PCM is programmed to see between the pre and post-cat sensors. Now your PCM is messing with your A/F ratio trying to find one that will bring the readings into the proper range - hence the fuel economy issue.

You can also invest about $5 and do the "non-fouler trick" (see my DIY in the FAQ section) which will get rid of the CEL by simply moving the post-cat sensors out of the direct path of the exhaust flow...

 

Agree with doing non-foulers. I have them on mine and they work. But to add to what has been said, check for any cracks in the exh manifolds or broken exh manifold bolts that might be leaking air

 

I completely forgot about the non-fouler trick. I'll do that today after work and clear the cels

 

Well I did the non foulers and it fixed the cat codes and now I'm getting a p2096 for fuel trim system 1 lean.

 

I was running a tad lean after the header install with the SC 91 tune combo but not lean enough to generate a CEL. According to the A/F band, the 180* thermostat richened up the mix almost right back to stock spec. Surprised with the cooler t-stat you are that lean.

For sh*ts and giggles, switch clear the code and switch to the tow tune and see if it stays gone. The perf tune really advances timing a lot...

 

Cleared the codes and switched the tune to towing. So far no CELs. Hopefully it doesn't come back when I do the cam swap.

 

Last year my 2002 ram 4.7 had this problem but it turn out the PCM was messed up and fails to work properly. So I had it replace to a newer PCM and nows it work fine. I don't remember the code but I sure that was the problem cause I heard that models from 2002-2006 had issues with PCM failure.

 

PCM would be the last option for these CEL's.

 

Well I after about a week of driving the darn code came back so I cleared it and returned the vehicle to a stock setting to see if that would help and as my luck runs it didn't. I guess I'll start running over the exhaust system and checking it for any possible leaks.