any ideas about poorly running xj

[256offroad]

My dd has started missing at random times. Mostly this past weekend while i was wheeling. It would only do it when it was parked awkwardly and i would get in it, start is up, and drive off it would miss very bad. To get it to clear up i would give it more throttle. it never does this driving around town except when its been sitting for awhile and i accelerate heavily. it misses and backfires through the intake then clears up and runs fine.


its a 96 with 130k miles
no codes are up
it gets barely gets 14mpg (has 4.10s and 32" terra grapplers)

i have replaced both o2 sensors and fuel pump and nothing else

i have a crap ton of spare throttle bodys with spare sensors on it so im thinking about swapping out some sensors and seeing what it does.

hardest part is it is VERY random when it does it. but im kinda thinking this is why i get poor fuel milage.

dont have much time to mess with it.

im thinking tuneup (sparkplugs, wires, cap and rotor) as well as a good seafoaming. and maybe try the sensors.

any other ideas? i hate chasing down these problems... ive done some searching on here but not much luck.

 

[jeepgeek2002]

check the usual stuff like distributor cap loose? or cracked..
Plugs should be a light grey on the tips.
wires .. check for cracks. splits and burns.

sometimes its the easy stuff that stumps us!

 

[souske]

Just went through this on my 96

Any codes?
My cap + rotor were sub optimal, but the real fault was ittermittent CPS failure. Talk about a hassle to troubleshoot, checked for spark, got good spark, ran like crap. Replaced the CPS and all is well again.

 

[256offroad]

ill try these. ive got all the spare sensors just have to find time to do trial and error.


biggest problem is it will run fine if i go out and crank it up. and may not miss at all...

its very random. but did it alot more wheeling.


think this is a tie to my poor fuel mileage?

 

[souske]

Check engine light?

Mine also died while wheeling, had to get towed 130 miles home
Thank goodness I have made some excellent friends through this club

 

[jeepgeek2002]

my wifes jeep died a bunch times.. when we went to morris mountain.. new alternator fixed it. go figure

 

[256offroad]

no check engine light.... runs good 95% of the time other than the poor fuel mileage.

 

[Jamescad04]

I would start with the tune up like you said, But if it continues you may want to try the catalytic converter. Mine went bad and was causing my O2 sensors to fail prematurely.

 

[stumpXJ]

Kinda hard to diagnose over the interwebs, but I have two 96 cherokees, and both of them gave me intermittent running problems like you mentioned at some point in their lives, and both times a new coil fixed the problem. The original coil was cracked along the back side and intermittently arcing to the engine block. Its easy enough to swap it out and see...

 

[256offroad]

I would start with the tune up like you said, But if it continues you may want to try the catalytic converter. Mine went bad and was causing my O2 sensors to fail prematurely.

Yeah its got a 2 year old magniflow cat and flowmaster.

Kinda hard to diagnose over the interwebs, but I have two 96 cherokees, and both of them gave me intermittent running problems like you mentioned at some point in their lives, and both times a new coil fixed the problem. The original coil was cracked along the back side and intermittently arcing to the engine block. Its easy enough to swap it out and see...

Yeah Im gonna try that and see


Just filled up and got 10mpg last tank something ain't right. But u just changed the throttle body(with a 63mm) and sensors out so we will see how well it does this go round


posted using my 4g, fast as hell, Verizon phone via tappatalk

 

[shortxjdoug]

what stump said..... check the coil..... other than that it sounds like an intermittent cps issue, ive seen it happen before

 

[UNCC_99XJ]

what stump said..... check the coil..... other than that it sounds like an intermittent cps issue, ive seen it happen before

Ditto. The bad thing is poking around with a multimeter looking for the usual signs won't do you any good if it's only intermittent. I hate intermittent problems!

 

[shortxjdoug]

Ditto. The bad thing is poking around with a multimeter looking for the usual signs won't do you any good if it's only intermittent. I hate intermittent problems!

ive not seen a lot of intermittent cps problems, but i have seen one on an older jeep i had a while back