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P0303 Misfire.

G

garciaxj88

NAXJA Forum User
Location
yuma,arizona
Heres the deal. Bought a 2000 xj 4.0 about a month ago. i put new spark plugs in last thursday and the following day i had a check engine light. got misfire in cyl #3. so i thought well maybe the i had a defective plug so i swapped it for one of the ones that came off it before and same code came back. did some research this morning and found a TSB for this code and the injector heating up and required the install of an insulator. i got one from the dealership put it on same thing, i swapped injector 3 with injector 1 and nothing changed. so my guess is the coil pack? it doesnt look broken, the boots look fine and no other misfires are happening. i tried looking in the dark to see of maybe the spark is grounding out on the head but nope. looks fine to me. so anybody got suggestions before i spend some money on a damn coil pack?
 
That's a tough one....I have had a coil pack go bad. I forget the exact misfire code I was getting. The resistance even checked out good on mine. Do you know anyone else with your year XJ? Reason I ask is that my I swapped my buddies coil pack into mine before buying one. It would take the guess work out of it.
 
That fuel injector insulator TSB fix from Jeep doesn't work for most people. Heat soak is very common on your vintage (00-01).

Many have added a timer that keeps the e-fan on for a determined amount of time when you turn off the engine to reduce temps under the hood. Others have cut in louvers into the hood. Some have done both.

Heat soak could very well still your issue. SEARCH for lots of information on it.

The one caveat that I will add is this. Are you using any coolant? If so, there is also a probability of a cracked 0331 cylinder head, which is what the 00-01 came with from the factory. That head has a casting defect between cylinders 3-4, which make it a target for cracking at that spot. And the #1 symptom of a cracked 0331 cylinder head is "unexplained coolant loss". Misfire on cylinder 3 or 4 can also happen.
 
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im gonna get the part today. the misfire doesnt feel bad. infact my jeep feels fine. i do feel a slight misfire when taking off other than that its not bad.
 
Sounds like heat soak to me. I had the same code earlier this year and have had no coolent loss. Its very common in our years XJ's to get the cylinder 3 misfire due to heat soak. Also like his mine runs like a top besides random small leak codes.
 
I would swap two of the new spark plugs, say #3 and #1 first. Then maybe check compression on #3 if it is not the plug(s).
 
So here are my findings. I bought a new coilpack and some different spark plugs. And guess what....did NOT fix it. But i did pay attention to some details.
When I was done with the instillation I drove the jeep around my block a few times and let it sit for 5min then started it back up and felt fine. Did not feel a misfire and let it idle for about 15min and it was still good. Then i let i sit for about a half hour until it came time to go to my inlaws house and ran fine and had no check engine light. Well we stayed there for about 3hrs last night and when it came time to go home the dreaded check engine light came on. The thing is it didnt even feel like it was misfiring either. Any ideas?
 
Short of pulling the head, one last thing to try would be to swap the #1 and #3 fuel injector. Also do a compression test on #1,2, and #3 and #4 cylinders and post the data here.

If it is a coolant leak (cracked head or head gasket leak), you might try one of the mild versions of Bars Leaks radiator-head coolant sealer as a temporary fix.
 
i already swapped injector 3 with number 1 before i installed the coilpack. im gonna try a much better insulation with all the injectors and on the fuel rail and see if it makes a difference. thank you ecomike ill try the compression test when im able to get my hands on a compression test gauge.
 
garciaxj88 said:
i already swapped injector 3 with number 1 before i installed the coilpack. im gonna try a much better insulation with all the injectors and on the fuel rail and see if it makes a difference. thank you ecomike ill try the compression test when im able to get my hands on a compression test gauge.
Click to expand...

Keep in mind the injectors need to be able to cool to ambient air, when you insulate!!!
 
when my buddys 2000 had heat soak we did the mopar injector wrap, didnt fix it, but got a bi better. then we added some decent hood vents. that seemed to fix it for the last year or so. Id suggest hood vents if compression checks out good.
 
The first question is can you stop the source of the heat from getting to the injectors (insulation), then if not, can you cool them better and faster.

Computer CPUs use aluminum fins called heat sinks, with a mini fan!!!
 
Gotta answer this question.

Are you having to add any anti-freeze to your reservoir lately? Are you keeping close tabs on the level?

The cylinder head is still a wildcard here...... it always is with the 00-01. The 0331 head is a dog.
 
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Well this morning I cleared the code. I was reading on another forum that discussed the heat soak problem. A couple of guys were saying accelerating on startup helps. And I prop open the hood. I've yet to have a misfire. I bought insulation wrap that one guy used so I'm gonna try that tecnique and see how it works. As far as coolant goes I haven't checked since I bought it last month.
 
garciaxj88 said:
As far as coolant goes I haven't checked since I bought it last month.
Click to expand...

Check your coolant level. All you gotta do is look at the bottle.

And as an owner of a 2000, you should check that level at LEAST once a week.

If you are unlucky and that 0331 head of yours cracks, you do not want to delay in the repair as coolant mixed with oil trashes the engine bearings in short order.
 
My 2000 had the wiring loom chaffed on the fuel rail in the back. Cleared and taped it and the problem is gone.
 
alright guys here is an update on my problem. since the weather has gone down in temperature i havent had any problems with misfiring. my jeep is running great right now. as far as coolant goes it doesnt seem to be consuming any coolant as i check the level every two weeks. it does have a nice rear main seal leak but thats besides the point.
 
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