A lean mixture aggravates a NOx concern. What Bill says carries some
weight, but you are probably looking to fatten it up, not lean it out more.
Vacuum leaks, bad O2, look for obvious things that are going to lean it out.
A fresh cat will make it pass, but be sure that you aren't just masking the
real problem, because it will fail again next year if you don't get to the
root of it.


Juice


"The Hurdy Gurdy Man" <bryan@linux.webicommerce.com> wrote in message
news:EQSzc.53068$TR1.51639@nwrddc01.gnilink.net...
>
> Did the 1994 Wrangler YJ 4.0L engine have an EGR system of any kind? I
> ask because I have one here that just failed its California smog test due
> to high NOx levels, which as I understand it is most commonly caused by an
> EGR failure, but I can't seem to find an EGR system anywhere on the
> engine. In fact I can't seem to find much of anything that can be tuned
> or repaired to help this situation other than changing out the catalytic
> converter, which I'm trying to avoid. The timing is supposedly
> unchangeable (so says the Jeep service manual), and every other part
> normally touched in an extensive tune up is brand new. New cooling system
> components, too. If it's true that there is no EGR system that can be
> checked, then I'm sort of left with the converter but I wanted to ask
> first to make sure I'm not overlooking something. Thanks!

 

A lean mixture aggravates a NOx concern. What Bill says carries some
weight, but you are probably looking to fatten it up, not lean it out more.
Vacuum leaks, bad O2, look for obvious things that are going to lean it out.
A fresh cat will make it pass, but be sure that you aren't just masking the
real problem, because it will fail again next year if you don't get to the
root of it.


Juice


"The Hurdy Gurdy Man" <bryan@linux.webicommerce.com> wrote in message
news:EQSzc.53068$TR1.51639@nwrddc01.gnilink.net...
>
> Did the 1994 Wrangler YJ 4.0L engine have an EGR system of any kind? I
> ask because I have one here that just failed its California smog test due
> to high NOx levels, which as I understand it is most commonly caused by an
> EGR failure, but I can't seem to find an EGR system anywhere on the
> engine. In fact I can't seem to find much of anything that can be tuned
> or repaired to help this situation other than changing out the catalytic
> converter, which I'm trying to avoid. The timing is supposedly
> unchangeable (so says the Jeep service manual), and every other part
> normally touched in an extensive tune up is brand new. New cooling system
> components, too. If it's true that there is no EGR system that can be
> checked, then I'm sort of left with the converter but I wanted to ask
> first to make sure I'm not overlooking something. Thanks!

 

A lean mixture aggravates a NOx concern. What Bill says carries some
weight, but you are probably looking to fatten it up, not lean it out more.
Vacuum leaks, bad O2, look for obvious things that are going to lean it out.
A fresh cat will make it pass, but be sure that you aren't just masking the
real problem, because it will fail again next year if you don't get to the
root of it.


Juice


"The Hurdy Gurdy Man" <bryan@linux.webicommerce.com> wrote in message
news:EQSzc.53068$TR1.51639@nwrddc01.gnilink.net...
>
> Did the 1994 Wrangler YJ 4.0L engine have an EGR system of any kind? I
> ask because I have one here that just failed its California smog test due
> to high NOx levels, which as I understand it is most commonly caused by an
> EGR failure, but I can't seem to find an EGR system anywhere on the
> engine. In fact I can't seem to find much of anything that can be tuned
> or repaired to help this situation other than changing out the catalytic
> converter, which I'm trying to avoid. The timing is supposedly
> unchangeable (so says the Jeep service manual), and every other part
> normally touched in an extensive tune up is brand new. New cooling system
> components, too. If it's true that there is no EGR system that can be
> checked, then I'm sort of left with the converter but I wanted to ask
> first to make sure I'm not overlooking something. Thanks!