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Help Please!! Intermittent Miss on Highway

T

tcpoland

NAXJA Member
NAXJA Member
Location
Utah
As stated above I have an intermittent misfire when I am on the highway... it usually comes in pulses ie it will misfire for a few moments and then go away for a day or two. My xj has always run great until last week it started missing and idled rough and died a couple times... it threw codes for the TPS which I replaced and now it downshifts normally and idles fine. However once every couple days while at cruise on the highway ( around 2k rpm) it will start to misfire for a second or two and once i tap the throttle it clears up. I am having a hard time figuring this one out... if you could please help that would be great. I also changed my plugs and cleaned the connections for the map tps and ckp.
98 XJ 4.0 219k
 
I have been wondering if its the crank sensor... I dont want to replace it if Im not sure so I thought id see if i coukd diagnose something else first
 
my first thought was TPS, as your code said... but youve replaced that. curious, did you pull the negative to the batter before installing? this will put your computer into a "relearn" mode immediately, where as if you just replace it and go, it may take a while for the computer to readjust for the new (properly working) sensor.

if you did that... CPS. its not hard. lots of extensions, a universal, and an extra set of hands makes it easy.
 
MY gut feeling is CPS/TPS related .
 
Pile ON!

Might be CPS thermal failure starting.
 
Inspect the wiring harness for exposed wires. I had a similar situation. The wiring harness that ran behind the head was rubbing against one of the studs.
 
You said you checked/changed the plugs...BUT even if you changed your plug wires check them (the wires) again. I'd even recheck your plug gaps. I bumped a gap to nearly closed once and had some issues.

My MJ had a miss nearly identical to what you are describing. My #3 plug wire had come apart on the inside and was not visually apparent.

Just one more thing for you to check if you have not already.
 
karstic said:
Inspect the wiring harness for exposed wires. I had a similar situation. The wiring harness that ran behind the head was rubbing against one of the studs.
Click to expand...

^this, and/or disconnect the three plugs on the ECU, blow them out (gently, low pressure) with compressed air and reconnect.

I had a #5 injector misfire that I diagnosed seven ways from Sunday. Could not find the problem until I cleaned out the plugs at the ECU.
 
So i replaced the cks with one from the dealership. After i finished the replacement and I got out from under the car I noticed a small piece of metal stuck to the magnetic side of the old sensor. Could this have potentially advanced my timing a bit or messed with it. Im thinking I will hold onto the old one to have as an emergency spare as it was still mostly functional it seem. Im just curious how well I should expect it to function should I ever need it.
 
Well, how is the issue now with the new crank sensor?
 
So far so good. I think the new cks has solved it. I guess my new question is do you guys think the bit of metal on the old one might have been responsible for it running rough like the timing was off?
 
tcpoland said:
So far so good. I think the new cks has solved it. I guess my new question is do you guys think the bit of metal on the old one might have been responsible for it running rough like the timing was off?
Click to expand...

Tough call. If it was causing an interruption in the field? Keep it for a limp-home spare. Post up if the problem presents itself again.

Hope you got it dealt with.
 
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