What codes do you get exactly, when you load the stock tune back on? The longtubes and catback shouldn't have anything to do with a MIL, but I could see it throwing a code for the downstream O2 sensors if you have no cats, or if the downstream O2 sensors are somehow turned off in the tune. Knowing the codes with the stock tune is really the key here to finding a solution to the issues you're experiencing. You may have a hard fault of some sort, which the tune is changing parameters and ignoring a fault condition.
Hey guys, I saw this thread in 4.6 Tech and copied it over here for some more suggestions, since it's an S197 that's having these issues. I left the original thread in 4.6 Tech for a bit more exposure and suggestions on getting it fixed.
I would assume that the issue is with the rear O2 sensors and your longtubes. This theory also assumes that you do NOT have catalytic converters, which would cause all of the codes you mentioned. If you don't have cats, you will fail the emissions visual regardless of what codes are being thrown. Check and see if you still have the catalytic converters installed or not, and get back to us.... With long tube headers, it is very possible that the cats have been removed.
JDM Fixed it !! - All, listen to this. I brought the car to Jim at JDM Engineering. He verified that all of the sensors were working, cats are there, etc.. They were unsure what was causing the issue, but did say that the JBA headers were "Very" Long. He modified the tune to increase the monitor temp of the rear O2 sensor. We loaded the tune and he hooked the car up to more monitoring gear. We ran the car for about an hour (not moving), but the same 3 monitors still said inc. He suggested that I put some miles on the car and maybe stop back to check again. I left and while I was driving, hooked up my OBD Scanner. After 3 miles, the O2 Monitor and O2 Heater Monitor went green (complete). I couldn't believe it. I drove straight to the NJ State Inspection Center. The Inspector Immediately opened the hood for a look, but went on with the inspection. GOT MY STICKER !! It Passed !! I have to say if you guys need a real pro and expert in stangs, go to JDM. They are unbelievable and great guys to work with. Thanks to all for your suggestions !! JDM is the BEST ...
Call Cody at Stang-Hi performance in Baton Rouge, LA his number is 225-751-4321 he is one of the few tuners to actually go to the SCT in house training. He has handled issues like this before.. race4food
