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cylinder 1 misfire - update

Kejtar

Kejtar

PostMaster General
NAXJA Member
Location
Westminster, SoCal
OK, so here's the scoop:
- 97XJ manual transmission
- Started throwing cylinder 1 misfire code after pulling it out of the driveway where it was parked for just over a month.
Since then I have:
- Replaced the distributor (my old one was a wee bit wobbly)
- Replaced cap and rotor
- Replaced plug wires
- Verified that I get spark to cylinder 1 (I got an inline spark tester where it shows spark as it occurs)
- Swapped plugs around (misfire stayed with the cylinder)
- Checked compression: compression is good
- Checked vacuum and it seemed stable (though I had a cheap vacuum guage)
- Swapped injectors around (misfire stayed with the cylinder)
- Bypassed the harness from the PCM to the injector (No change)
- Swapped in a different PCM (No change).

NOw here's what I"ve observed: It seems that when the engine is cold at idle the misfire does not really happen till the engine warms up.

So far that last item is my only clue!

Anyways, this is frustrating: I had couple wheeling trips I wanted to go on but at this point I can't cause the jeep is not doing good :(
So any ideas/thoughts as to what is wrong and how to fix the damn thing are welcome....
 
I've heard of the CPS acting up only when they are hot it could be an 02 sensor as well. As for the lifters not necessarily all the time if the lifter is leaky the more it expands the more it will leak. Mine does this intermittently only when it's hot like after I've driven it on the highway for a few hours, it goes away after it cools down and never goes it around town. Any codes?
 
Ok, the CPS thing can probably be thrown out as I'm not getting any CPS codes at all. Also if it was CPS it'd probably mess up more then Cylinder 1.

Codes? Yup: P0301: Cylinder 1 misfire.

02? hmmm again why only cylinder 1?

Btw, a short 10 minute trip will have it throwing the code.... but when it's parked in a driveway it can run 20 minutes and not throw a single one.
 
I'd start with testing the sensors at least and see if they test OK. If they test good I would pull the valve cover and make sure everything looks like it's working and nothing is bent or loose. Also sensors may not always throw a code right away it could take a few trips. Good luck with it.
 
robsjeepxj said:
I'd start with testing the sensors at least and see if they test OK.
Click to expand...
Testing CPS ain't easy and even then the test is considered not reliable (heck if it was easy it'd throw a code reliably ;) )
I would pull the valve cover and make sure everything looks like it's working and nothing is bent or loose.
Click to expand...
That's probably next weekend.
Also sensors may not always throw a code right away it could take a few trips.
Click to expand...
I've had plenty trips short and long to throw that code
Good luck with it.
Click to expand...
Thanks.
 
Ok, lets make sure we are all on the same page. The CPS/CKP crank sensor would effect all cylinders.

You switched the spark plug, injector, and spark plug wire. You changed the distributor cap and rotor. The misfire is staying with cylinder no. 1. Call me silly, but I would say the issue is with cylinder no. 1.

Ok, did you write down the compression test number for cylinder no. 1? Cold or warm? Warm the engine up for 20 minutes. Pull no. 1 plug, run a compression test on no. 1 hot. Compare the numbers.

There was a TSB out there on valves not rotating properly but I can't remember the specifics.

You could have a galled valve guide in no. 1 that is only sticking after the engine warms up.

Do you still have the old spark plugs you removed? Did no. 1 have any issues?
 
Ok, did you write down the compression test number for cylinder no. 1? Cold or warm? Warm the engine up for 20 minutes. Pull no. 1 plug, run a compression test on no. 1 hot. Compare the numbers.
Click to expand...
I checked the compression on cold engine. IIRC it was in the neighbourhood of 140.... I'll have to check it warm.
There was a TSB out there on valves not rotating properly but I can't remember the specifics.
Click to expand...
Yeah.. but that should have shown up under 220K miles.....
You could have a galled valve guide in no. 1 that is only sticking after the engine warms up.
Click to expand...
;(
Do you still have the old spark plugs you removed? Did no. 1 have any issues?
Click to expand...
Plugs looked good.
 
There was another TSB on multiple misfires, but it was for later XJs than yours. Had to do with carbon build up.

Another thing, doing the toothpick synch sensor alignment in the distributor helps if the problem is related to timing chain stretch. Worth a look.

Good luck.
 
joe_peters said:
Another thing, doing the toothpick synch sensor alignment in the distributor helps if the problem is related to timing chain stretch. Worth a look.
Click to expand...
Never heard of doing an alignment on the distributor like that..... Regarding the timing chain stretch: wouldn't that affect more then just number 1?
 
Hey, spit-balling here!

Yeah, but maybe it depends on the amount of stretch/how far out of alignment.

PM me your email address, I have a file with a long article on it.
 
Yeah, but it is free and quick, and it eliminates one more possibility.

Another thing that comes to mind is weak valve spring/carbon. Wondering if some Seafoam or MCCC might help.
 
I have the exact same problem on my 98 4.0 5 Speed. Good compression, good mpg, good spark, but every once in a while (once or twice a month for the past few years) it throws the P0301 code. CEL always goes off after a few trips. Puzzling stuff!
 
arib said:
I have the exact same problem on my 98 4.0 5 Speed. Good compression, good mpg, good spark, but every once in a while (once or twice a month for the past few years) it throws the P0301 code. CEL always goes off after a few trips. Puzzling stuff!
Click to expand...

My code is not every once in a while.... it's guaranteed within 15 minutes of driving...
 
arib said:
I have the exact same problem on my 98 4.0 5 Speed. Good compression, good mpg, good spark, but every once in a while (once or twice a month for the past few years) it throws the P0301 code. CEL always goes off after a few trips. Puzzling stuff!
Click to expand...

This is EXACTLY what is going on with mine, 97 4.0l auto, new plugs/wires/cap/rotor... pulled injector one and switched with #6 still same same code as you. but again will come on then go off by itself... one time i got it to go off by while running at about 10mph i put the heep in N shut it off then back on again WHILE rolling, light went away and is still off.. dont know if its a sensor or what??:huh:
 
89xjJe3per said:
This is EXACTLY what is going on with mine, 97 4.0l auto, new plugs/wires/cap/rotor... pulled injector one and switched with #6 still same same code as you. but again will come on then go off by itself... one time i got it to go off by while running at about 10mph i put the heep in N shut it off then back on again WHILE rolling, light went away and is still off.. dont know if its a sensor or what??:huh:
Click to expand...

Can you hear the misfire? Can you feel the rumble as it skips 1?
 
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