Damon Dimick
NAXJA Forum User
- Location
- Portland, OR
So my gf's 93 HO 4.0 XJ failed the emissions test here in Oregon due to excessive NOx. It is originally a CA Jeep, and the previous owner put on an aftermarket air intake, but the motor is otherwise stock, 210k miles. It runs strong and doesn't have any other problems. I know that excessive NOx is due to excessive combustion temperatures and all of that. I was expecting to find an EGR valve, but I guess the 91+ 4.0's don't have one. Did the key on/off etc and no trouble codes came up. I'm sorry but I don't have the numbers from the emissions test showing how much it failed by. Also, I couldn't find any vacuum leaks.
I've read a few posts around the net about people having a hard time eventually finding the cause, even after replacing some parts such as the cat. Anyway, just wondering if any of you had any similar experience or solutions, and if any of those "guaranteed to pass" fuel additives actually work or if they would pertain to NOx problems. Would the aftermarket intake be causing a lean condition? Any help would be appreciated.
I've read a few posts around the net about people having a hard time eventually finding the cause, even after replacing some parts such as the cat. Anyway, just wondering if any of you had any similar experience or solutions, and if any of those "guaranteed to pass" fuel additives actually work or if they would pertain to NOx problems. Would the aftermarket intake be causing a lean condition? Any help would be appreciated.