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XJ Ask the Question Thread
Herp Derp Jerp
Join Date: Nov 2011
Location: Parham, ON
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Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
Well. I can tell you that yes, you have something wrong lol.
Start checking other sensors. Something is amiss.
Not the o2 sensor voltages, just the STFT @ LTFT %s. I did notice that the o2 sensor voltage (I believe it was upstream, [on second thought, it may have been both of them]) stuck at 1v for a bit after I turned the Jeep on. Is that normal or could it point to a wiring issue? I'll get more into this in the morning, but yeah. When I do do this is it okay if I drive around while I let it log? Shouldn't matter right?
CF Veteran
Join Date: Oct 2012
Location: Canton, GA
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Year: 1996
Model: Cherokee
Engine: 4.0
What do I check next? Hahaha. Sorry if I'm sounding a bit dumb, I just don't have any clue where I should be looking. IAC? TPS? Clean the TB?
Last edited by tssguy123; 01-03-2014 at 09:22 PM.
CF Veteran
Join Date: Oct 2012
Location: Canton, GA
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Year: 1996
Model: Cherokee
Engine: 4.0
CF Veteran
Join Date: Sep 2010
Location: Mercer County, NJ
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Year: 2001
Model: Cherokee
Engine: 4.0L I6 HO
Yup, once it warms up though. Here's an example of what you're looking for
That's not from a Jeep - because I'm lazy - but that demonstrates a mostly working cat. The signal from upstream represents the computer adjusting fuel to hit the 14.7:1 AFR. Obviously not a, er, fine work of art since it's constantly turning the amount of fuel up and down. Downstream should be a steady signal once warmed up as the catalytic converter smooths out all the crap. Compared to an XJ that graph looks like it's reading on the rich side with a higher downstream voltage. However, STFT and LTFT will tell you if it's constantly adding a ton of fuel or trying to lean it, or spazzing out and adjusting STFT wildly (points to a vac leak or some kind of other fail)
Herp Derp Jerp
Join Date: Nov 2011
Location: Parham, ON
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Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
Well I'll put it this way... the O2 sensors are regular maintenance items, the other sensors are not, lol. You could clean your IAT and check for vacuum leaks if you're bored. Also verifying temp sensor accuracy is always fun, IAT or ECT could be off.
CF Veteran
Join Date: Oct 2012
Location: Canton, GA
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Year: 1996
Model: Cherokee
Engine: 4.0
Can I just use TB cleaner to clean the IAT? I'm probably going to clean the IAC and TB tomorrow so I may as well... I know the o2 sensors definitely need to be done and they will be as soon as I have $60 to spare. Being broke sucks
Herp Derp Jerp
Join Date: Nov 2011
Location: Parham, ON
Posts: 18,251
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Received 13 Likes
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12 Posts
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
CF Veteran
Join Date: Oct 2012
Location: Canton, GA
Posts: 2,314
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Year: 1996
Model: Cherokee
Engine: 4.0
CF Veteran
Join Date: Sep 2010
Location: Mercer County, NJ
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Received 4 Likes
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Year: 2001
Model: Cherokee
Engine: 4.0L I6 HO
Oh and the tape on the map sensor works great for temp fix
CF Veteran
Join Date: Feb 2013
Location: Franksville, Wi
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Year: 1995
Model: Cherokee
Engine: 4.0
CF Veteran
Join Date: Oct 2012
Location: Canton, GA
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Received 3 Likes
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Year: 1996
Model: Cherokee
Engine: 4.0