94 Jeep Cherokee

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94 Jeep Cherokee

Jones
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Re: 94 Jeep Cherokee

Karupt
Well , are we talking in common sense terms or BAR terms ? Sometimes I wonder if BAR reps and employees are somewhere driving their cars in 2 nd gear on a freeway or highway .
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Re: 94 Jeep Cherokee

scanner
In reply to this post by Jones
I test a certain 94 Jeep Cherokee with standard size tires every two years, and if I do a run in 2nd gear only, it will fail for NOx at 25 mph like yours.  

I can only speculate as to what happens.   I would assume at the higher rpms, the exhaust is blasting through the cat, and not allowing the gases to reduce.   I think the ECM can only switch the A/F mixture at a certain maximum rate, and the cat never sees the lean-rich mixture switch needed to reduce NOx.  

I think the 2nd - 3rd gear run is legit.  There's nothing wrong with the vehicle.  

Why make it simple, when it will work equally as well complicated.
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Re: 94 Jeep Cherokee

Karupt
In reply to this post by Jones
as long as you ran the rpms into the red zone before you switched to 3rd , I see no problem.
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Re: 94 Jeep Cherokee

INLANDSMOG
BAR is looking for LOW RPM  numbers anyway
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Re: 94 Jeep Cherokee

kfworry
If the BAR is looking for low RPM's then they should lower the Max RPM's for ASM's.
They "write the software" then "ding us" for being within the RPM Software parameters.
It's a No Win situation.
High RPM's heat up the Cat more to reduce HC and CO.
NOX is a common problem with the 4.0 liter high output engine in the Jeeps.
If it runs a tad lean, 1.1 lamda, it will bust the Max NOX.
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Re: 94 Jeep Cherokee

FiendFX
kfworry,

what if lambda was .9 and it failed for max NOX?
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Re: 94 Jeep Cherokee

kfworry
I'd suspect a faulty NOX bed.
As a rule high HC and high CO lowers NOX, with a known good Cat.
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Re: 94 Jeep Cherokee

Moderator
This post was updated on .
1.1 lambda is very lean.  I think that scanner is on to the correct idea about the PCM's ability to react quickly enough to get a tight closed loop.  It was an issue with the feedback carburetor systems too, but none of them (or the Jeep for that matter) were designed with the idea that they would have to pass a tightened NOx spec in ASM many years later.  It seems like it was true then, and perhaps even more true now ... design something just good enough to (usually) make it out of warranty, and then you're on your own.
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Re: 94 Jeep Cherokee

bizarsmog
 OK , HOW is the nox problem fix without change CAT, any idea??
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Re: 94 Jeep Cherokee

Moderator
This post was updated on .
IMO, the state of California doesn't want the old vehicles on the road unless they are in perfect condition, and the tightened NOx limits are an indication of that.  You can fight it with a good ol' fresh O2 and cat, but it's not going to be a durable repair, because there's a high likelihood that the high-mileage engine is going to barf on them, and who knows what the revised cut-points are going to be in two years anyway ... I can assure you that they won't be relaxed.

I have seen it myself many times ... a vehicle runs nearly identical number two years apart, and the first set is a pass, while the second set is a fail, due to stricter cut-points.
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Re: 94 Jeep Cherokee

none
In reply to this post by kfworry
kfworry wrote
I'd suspect a faulty NOX bed.
As a rule high HC and high CO lowers NOX, with a known good Cat.
I would check the O2 sensor rise time first.
Good judgement comes from experience. And experience? Well that comes from poor judgement.
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Re: 94 Jeep Cherokee

Karupt
In reply to this post by kfworry
kfworry wrote
If the BAR is looking for low RPM's then they should lower the Max RPM's for ASM's.
They "write the software" then "ding us" for being within the RPM Software parameters.
It's a No Win situation.
High RPM's heat up the Cat more to reduce HC and CO.
NOX is a common problem with the 4.0 liter high output engine in the Jeeps.
If it runs a tad lean, 1.1 lamda, it will bust the Max NOX.
  Exactly , I wish the BAR would have this Eureka moment . it is much easier to just maintain the status quo.
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Re: 94 Jeep Cherokee

No One
In reply to this post by Jones
Everyone and their mothers always want to throw a new cat at these cars.