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miss fire every once and awhile on start up

XJ: 
2K views 23 replies 11 participants last post by  JeepInABox 
#1 ·
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
 
#7 ·
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.
 
#10 ·
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.
 
#12 ·
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
 
#13 ·
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.
 
#19 ·
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.
 
#16 ·
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
 
#20 ·
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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