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Replaced almost Everything

FastEddie505

NAXJA Forum User
Location
Michigan
ive looked for quite a while now all over and cant find someone that is/was in my boat. just got into this 99 xj about a month ago now and have replaced both o2 sensors ( periviouse owner had cut front o2 sensor plug off so i had to wire it back together) , intake gasket , banks header , 4 hole injectors , iac/tps , plugs and wires valve cover gasket , new oil change , cleaned tb twice , new cts , jeep is straight piped. may be missing somthing but heres my problem .it idles rough feels like it has a miss but never thrown any codes for one , will blow black exuasht . and has a God awful poping/crackeling noise from exhuast between 2k-3k dose not do it above or below maybe not enough back pressure ?? cant figure out what is going on . starting cold is much easyier than after it is warm , some times i have to try two or three times . everyone says its the o2 sensors but this would be the third time ive replaced them.


forgot to mention that i also have a cel for the tps and iac system


first jeep and im all ready loving it!!!!
 
You need to check the O2 sensors while the engine is warm and running crappy while
using a code scanner with graphing capability (not just a code reader). You want to see
a series of rapid, sharp, peaks and valleys all along the graph. If you see any long flat
spots or dead gaps along the graph then chances are good that you have a problem in
the O2 sensor wire harness.

I had this exact problem that drove me nuts for several months, last year. Did the same
as you and replaced the O2 sensors, twice. No improvement. I got a scanning app on
my iPad (Dash Command) and I found that the graph for the forward O2 sensor had
long, random flat spots and dead areas.

Then, I checked the wire harness - from the O2 sensor connector - to the forward-most,
black harness connector at the ECM - using a beeping continuity tester (it's one of the
features on my digital multimeter).

I found a badly repaired, crimped, splice inside the corrugated O2 sensor wire harness
(by the previous owner) in the harness between the power steering pump and the
hard black plastic cover near to the thermostat housing. I cut away the crimp, twisted
and soldered the wires together, and double-heat shrink wrapped the splice - just as
recommended by the FSM.

No troubles since.

I now have 2 sets of almost brand-new NTK O2 sensors sitting around as spares.

1998 XJ, 2WD, 4.0L, automatic.
 
Yes it dose just replaced both and I got a flat line for volts on both sensors. Also replaced cap and rotor seemed to help out just alittle
 
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