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Old October 9th, 2013, 09:12 PM   #1
2000xjforlife
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miss fire every once and awhile on start up

i have a 2000 xj with a 4.0 only thin aftermarket done to the motor is a throttle body spacer and i had the missfire before i installed that it only happens once and awhile on start up and if u rev it it goes away im hopeing it doesnt have anything to do with the direct igntion
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Old October 9th, 2013, 09:16 PM   #2
firehawk
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Ever give her a tune up?


Plugs, wires, fuel injector cleaner..........?
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Old October 9th, 2013, 09:44 PM   #3
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This is coil on plug I believe, tune up x2...
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Old October 9th, 2013, 10:27 PM   #4
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My tj did the same thing it was worse when warm. Mine just stopped doing it on its own so i guess im no help here

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Old October 10th, 2013, 07:02 PM   #5
2000xjforlife
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ive gave it a tune up wich just consist of new plugs correct since its direct igntion theres no wires unless it consist of these boots i just found on azs website i mean i keep up on maintenance ad u run lucas injector cleaner atleast once a month
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Old October 10th, 2013, 07:04 PM   #6
2000xjforlife
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ya its coil on plug has one long bar with all of them in one i just found u can buy these boots and new springs for the coils think i might try that
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Old October 10th, 2013, 07:09 PM   #7
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Those coil packs can develop cracks and cause a miss. I have gone though a few of them (OEM and aftermarket) They are starting to stock the replacement ones at the local parts stores because they brake that much.

You can do a buy online from Advance Auto and use promo code trt30 for 30% off. Its a lifetime warranty also.
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Old October 10th, 2013, 07:57 PM   #8
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Cracked head
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Bare Bones Offroad
RIP FS4L
2 old xj's
Meow
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Old October 12th, 2013, 09:22 PM   #9
2000xjforlife
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ya ill have to replace that and ya its not a cracked head lmao
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Old October 13th, 2013, 10:37 PM   #10
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Do know what cylinder is misfiring? Most common is #3 cylinder misfire, there was a TSB released which more or less consisted of a corigated cardboard tube that got zip tied around the #3 fuel injector to shield it from heat. The few that I have done corrected it misfire issue.
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Old October 14th, 2013, 08:33 PM   #11
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no i dont know wich one is missfireing all i know is it missfires once and awhile on start up never when its hot or when im rageing on it or wheeling or anything like that
it only does it when its cold
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Old October 14th, 2013, 08:35 PM   #12
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well i have to correct my self it has done it when it was hot like the other day i drove it all the way to work wich is like 50 miles never missfired one time got to work parked and like 5 mins later i had to move it started it up and it missfired and i had to rev it up to get it to stop
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Old October 15th, 2013, 11:22 AM   #13
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I have the same problem on my 01XJ. I have replaced most of the components you would think we be a problem and it continues.

I found a thread on a XJ forum a while back that said it is a problem with the check ball in the fuel pump assembly that fails and lets the fuel pressure drop in the feed line. Instead of having fuel pressure at the rail on startup, the pump is still trying to prime the fuel system and causes the misfire due to lean/fuel starve conditions. The advice was to replace the unit, or key the jeep on and off a few time to prime.

I key mine on 3 times and no misfires.... occasionally it will do it, but not like it used to.

Hopefully that helps... I would at least try that and see if it continues. Other than bit of advice, I have no idea..., but it's working on my Jeep.
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Old October 15th, 2013, 04:26 PM   #14
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ill try that cause ya it did it today i drove to the dealer wich is 10 mins away shut it off for like 5 mins go back out start it up and bam it was missfireing and had to rev it up acouple times and it went away
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Old October 15th, 2013, 09:24 PM   #15
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where would i get that part your are speaking off Jeff that goes around #3 fuel injector im try all cheapest to most expensive
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Old October 15th, 2013, 09:46 PM   #16
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Like punisher said, Jeeps are notorious for the in tank fuel pressure back flow preventer aka check ball for failing. This causes long crank on some and could cause your concern. Check fuel pressure key on cold and see if it has to build a lot of pressure. Or just replace parts, your call. Diagnosis is for dummies anyways
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Old October 16th, 2013, 08:56 AM   #17
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Quote:
Originally Posted by Toivo View Post
Like punisher said, Jeeps are notorious for the in tank fuel pressure back flow preventer aka check ball for failing. This causes long crank on some and could cause your concern. Check fuel pressure key on cold and see if it has to build a lot of pressure. Or just replace parts, your call. Diagnosis is for dummies anyways
umm ok
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Old October 16th, 2013, 01:33 PM   #18
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I have seen the check valve go bad and the fuel rail lose pressure in seconds after shut off. Put a pressure gauge on it and run it till it stops missing, then turn it off and watch the gauge, check In 1, 5, 10, 30, 60 minutes should not drop more then 10% in 24 hours
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Old October 19th, 2013, 10:21 PM   #19
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Originally Posted by 2000xjforlife View Post
where would i get that part your are speaking off Jeff that goes around #3 fuel injector im try all cheapest to most expensive
Local dealer, there is a service bulletin out for this problem. The way the newer style manifolds are designed it directs the heat at the #3 injector. However both my 01 and 96 XJ's will run rough when I am working them or it is hot outside......even with the injector insulated. I would lean away from the fuel pump check valve being the fact that if the check valve had failed and would bleed off pressure, this would also cause a long crank time on first start up (like ten seconds plus) cant hurt to check it anyway if you have a fuel pressure gauge.
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Old October 21st, 2013, 07:46 PM   #20
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ya it always starts right up but i got a update on this i do belave it is the fuel pump cause last night i went offroading in my friends man made off road park and my jeep got stuck on a hill where the back of my jeep was way in the air and the front end was buried was at least a 45 deg angle at least it was running fine when i turn it off to go get the tractor to pull me out and when i got in my jeep to start it it would not start at all just turned over and over again i actually had to get in the gas to get it to start and when it started it misfired bad and barely wanted to run then i had to rev it like 4 times and then it was running fine but my buddy was like oo classic jeep stuck on a hill its not getting gas lol but i really thought about what Ive heard on here from everyone makes me really think it is the fuel pump what u all think?
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