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97 xj with running rough

85xjwoody

85xjwoody

NAXJA Forum User
Location
Little Suamico Wi.
I am working on a 97 xj 4.0 auto and trying to track down why it has a miss in the engine. I know my way around an xj and this one has me stumped. I have replaced the following:

Plugs
wires
cap
rotor
TPS
IAC
MAP
CPS
CAM
ignition coil
injectors
computer
fuel pump

I have also taken off the valve cover to check for a stuck lifter and all is functioning properly, also the cat converter is not plugged either. I am stumped as to what the problem could be as I believe I have covered most of what could cause this problem. I also put a breaker bar on the crank to see if there was excessive play in the timing and there is no play. Any thoughts and suggestions are greatly appreciated, oh and it is not throwing any codes at all.

Kim
 
I'd be tempted to pull the injector wires one at a time and listen for a change.

Then maybe pull the plugs one at a time and compare them. If one plug has noticeable more carbon than the others, you have at least narrowed the problem down some.

Vacuum leaks, most of the vacuum connections are off center on the intake manifold. So if one is leaking you may have some cylinders running a little lean and others running a little rich. Same with loose intake/exhaust manifold bolts.

The wires in the injector harness, where it makes the bend at the firewall have a tendency to separate/break the individual copper threads under the insulation. Might show up with a noid light test.

What does your exhaust look and smell like? Rich, normal, lean?

Compression test.

Just some ideas.
 
I have gone through all the vacuum lines and all are good. All injectors are working properly also. Exhaust smells rich. Exhaust manifold/intake gasket is good and bolts are tight. I am beginning to think the distibutor is off a tooth but there is no backfiring out the exhaust or intake.
I took the valve cover off to and turned the motor off all is moving and functioning properly. The plugs only have a few minutes of run time I will check tomorrow and see if any look different than the others.

Thanks for the help
 
Fully describe the conditions under which the miss occurs, and does not occur. Why did you replace all those parts ? Have you tested the O2 sensors ? have you tested the Coolant Temperature Sensor ?
 
From start up whether cold or warm it has a rough idle but will idle. If you give it gas while in park it seems to almost rev normally but you can tell there is still a miss somewhere. When you put it into gear you feel power loss but can still turn the tires over just not as you should be able to.
Trust me I didn't spend money on all the parts I have replaced, I have swapped them out with parts from my wheeling rig that are good and working parts. Parts that are new are cap, rotor, wires, and plugs. I have not tested the O2 sensors as they should not be part of the problem, if they were they would not start showing problems till after reaching warm up temp. Am I wrong on this? I did not test the coolant sensor but swapped that out also and still the same miss. I will be checking the plugs here in a bit to see what they look like.
 
Just checked all the plugs and all smelled of raw fuel and almost fouled out they looked so shitty, and only a couple minutes of run time on them.
 
Was or is the CEL light on ? Did the symptoms suddenly appear or did they get slowly worse ? What diagnostic testing has been performed ? Do you have an ODB-II scanner or smart phone app that can provide live data ?
 
verify a solid vacuum signal to the MAP sensor-- if it's not a strong intake vacuum, the MAP will relay that info to the ECU and it will richen the mixture to assist in the "under load" condition that it thinks you're operating under.
 
you'll want a vacuum gauge, a hose, and a tee to hook everything in line. A realistic reading would be in the 16-18 range with it idling. There's a lot that can be told about the condition of the engine with a vacuum gauge, so it may not be a bad investment in diagnostic tools (usually only about $20.00)
 
b5bde6e3eea59b072b7f827660bb2263.jpg



Can anyone spot the problem? :)
 
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