Emissions fail. Need help
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
There is no EGR so don't waste your time looking for it. That function is handled by cam overlap.
Is the motor running hot? What do the plugs look like, overheated by any chance?
NOx is often caused by combustion temps that are too high. Running a bit lean will do it, could be O2 sensor, as mentioned. Carbon deposits, plug heat range too high, an injector or two not operating correctly..
There is a good possibility your cat is diminished. High oxygen numbers kill the cat's ability to clean up NOx, but yours are very low. It should be able to clean that up, yet isn't.
Is the motor running hot? What do the plugs look like, overheated by any chance?
NOx is often caused by combustion temps that are too high. Running a bit lean will do it, could be O2 sensor, as mentioned. Carbon deposits, plug heat range too high, an injector or two not operating correctly..
There is a good possibility your cat is diminished. High oxygen numbers kill the cat's ability to clean up NOx, but yours are very low. It should be able to clean that up, yet isn't.
Thread Starter
Junior Member
Joined: Apr 2012
Posts: 33
Likes: 0
From: san diego ,CA
Year: 1994
Model: Cherokee
Engine: 4.0 ho
Yeah first test was with 91 octane. I then siphoned 7 gallons out and put in 87 octane to try with the pre-test and nox was worse.
Thread Starter
Junior Member
Joined: Apr 2012
Posts: 33
Likes: 0
From: san diego ,CA
Year: 1994
Model: Cherokee
Engine: 4.0 ho
So i took my jeep to the family mechanic who did some diagnostics. He replaced the catalytic converter and now it passes nox at 25mph but fails at 15. He said its running too lean. What else can i do? Would it help to swap injectors (dodge neon).
Thread Starter
Junior Member
Joined: Apr 2012
Posts: 33
Likes: 0
From: san diego ,CA
Year: 1994
Model: Cherokee
Engine: 4.0 ho
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Thread Starter
Junior Member
Joined: Apr 2012
Posts: 33
Likes: 0
From: san diego ,CA
Year: 1994
Model: Cherokee
Engine: 4.0 ho
Update: ran a tank of the 44k, injector upgrade and decarb. Still failed on nox. Both speeds were around 1400ppm. After the test I checked compression: cylinder
1= 130psi
2= 135
3= 140-145
4= 135
5= 145
6= 145
Talking to the previous owner (2nd owner) the motor has never been rebuilt to his knowledge.
What should I do next?
1= 130psi
2= 135
3= 140-145
4= 135
5= 145
6= 145
Talking to the previous owner (2nd owner) the motor has never been rebuilt to his knowledge.
What should I do next?
Newbie
Joined: Jun 2013
Posts: 28
Likes: 1
Model: Cherokee
Have you checked your oxygen sensor? Can you post a picture of the test results after the cat was replaced? Nox this high after a converter replacement can be caused by engine running hot, carbon on the piston tops causing the combustion chamber to run hotter, exhaust leak before the converter that will bring in more oxygen and cause hc to go down but make Nox go up.
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Have you checked your oxygen sensor? Can you post a picture of the test results after the cat was replaced? Nox this high after a converter replacement can be caused by engine running hot, carbon on the piston tops causing the combustion chamber to run hotter, exhaust leak before the converter that will bring in more oxygen and cause hc to go down but make Nox go up.
Thread Starter
Junior Member
Joined: Apr 2012
Posts: 33
Likes: 0
From: san diego ,CA
Year: 1994
Model: Cherokee
Engine: 4.0 ho
Have you checked your oxygen sensor? Can you post a picture of the test results after the cat was replaced? Nox this high after a converter replacement can be caused by engine running hot, carbon on the piston tops causing the combustion chamber to run hotter, exhaust leak before the converter that will bring in more oxygen and cause hc to go down but make Nox go up.