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Proper timing advance... seems high

nrwphoto

NAXJA Forum User
Location
Appleton, WI
Alright this is a 98' Cherokee and to start off I know that you can't rotate the dist. cap to advance the timing... it's all computer controlled.

My delima comes from the readings I was getting from an OBD-II scan tool while on a recent test/trouble shooting drive. O2 voltage was within specs, which is good since they are both new. STFT and LTFT also looked fairly good from what I read online. Jeep was warmed up, drove 40mi trip just before hooking it up to scan tool, on a 90 deg. day.

Ok, was reading 18 deg. at idle, 42-45 deg. while running 65mph on flat ground in top gear, 35-38 deg. when taken out of OD... again flat ground, top gear with very slight grade was similar. During normal acceleration up on ramp the advance was around 27 deg. and would drop down to 23 deg. during full throttle. These numbers seem backwards to me. Seems like there should be more advance at full throttle and less at cruise. and running in the 40's on the freeway just seems rediculous to me. For brief moments during the test drive my passanger noticed as high as 62 deg. of advance in stop and go street light driving.:shocked:

Does this sound right, or do I have a bad computer or something?

Thanks
 
Alright this is a 98' Cherokee and to start off I know that you can't rotate the dist. cap to advance the timing... it's all computer controlled.

My delima comes from the readings I was getting from an OBD-II scan tool while on a recent test/trouble shooting drive. O2 voltage was within specs, which is good since they are both new. STFT and LTFT also looked fairly good from what I read online. Jeep was warmed up, drove 40mi trip just before hooking it up to scan tool, on a 90 deg. day.

Ok, was reading 18 deg. at idle, 42-45 deg. while running 65mph on flat ground in top gear, 35-38 deg. when taken out of OD... again flat ground, top gear with very slight grade was similar. During normal acceleration up on ramp the advance was around 27 deg. and would drop down to 23 deg. during full throttle. These numbers seem backwards to me. Seems like there should be more advance at full throttle and less at cruise. and running in the 40's on the freeway just seems rediculous to me. For brief moments during the test drive my passanger noticed as high as 62 deg. of advance in stop and go street light driving.:shocked:

Does this sound right, or do I have a bad computer or something?

Thanks


Compeared to the reading I get on my Scanguage, everything there seem completely normal. When I first saw those readings, I freaked out but quickly regained my composure when I remember that the 4.0 was not displaying drivability problems.
 
Matches what I see on mine. Thing is, until we had these tools (Scangage etal...) available, we did not know what, exactly, was going on in under the hood.

Surprising, isn't it?
 
Cool, thanks for the info, nice to have another Jeep to compare numbers with. Tried finding it at dealership and techs didn't know. All said that info was unpublished.
 
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