I bought some pacesetter long tube headers for my 08 JKU. I had a custom mid pipe made with new cats. The O2 sensors are extended. It worked fine with no check engine light for 2 days. Now my check engine light is on. I called RIPP about their Diablo programmer for use with the long tube headers they sell without supercharger. They couldn't tell me if it would work. So any advice from anyone who has a similar situation. How did you get CEL to go off? What programmer are you using?? Please don't waste your time with the you should have bought RIPP headers or drop a hemi in there. Thank you for any useful info.

 

I use VCM Suite from HPtuners.com -- although I'm not sure how to fix the problem. If you go this route, request the beta software because there are more options for the 3.8L JK engine. Just got though testing with Virtual Dyno, ~10 more HP on a second gear run compared to stock (PE Delay set to zero).

The scanner (data logger) in the suite is the first thing I'd use, and it works well. Get a trend chart of all four O2 sensors and see what's going on. There are adjustable delays and an ECT permissive for closed loop operation of the post-cat O2 sensors, maybe that would help if the new cat isn't lighting off as quick as it expects. Wondering about a time lag issue too. Are both the pre and post O2 sensors further downstream? It takes a while for the self diagnostic check, and that may be why it took two days to get the CEL.



Edit: Tuning via computer is new to me, so I may not know everything I think I know. But here's a thought: You probably bought the headers to get better VE (Volumetric Efficiency, better flow). But without PCM changes in a speed density system this extra VE turns into a leaner mixture at WOT. The PCM has VE programmed into a lookup table that has no way to know that there is more air due to a change in real VE, so in open loop full WOT there is the same fuel and more air. It may be a trivial amount, but I suspect I had to bump my VE up around 2% in the higher RPM range around 4K RPM due to a lower restriction muffler. Something I learned was to leave the PE delay at the stock 6 seconds and look really carefully at the upstream O2 sensors in the data logs to adjust VE at WOT. RPM's at WOT are not typically constant, and it took a while before I caught on to this -- don't rely on logging short or long term fuel trims for these brief time periods before PE kicks in. A wideband sensor would be nice, but I think this method worked fine too.