hi all, tia for any thoughts. have been combing the forums (great site)

Have a 99 xj 4L 5 speed 190k, has engine hesitation that I am trying to track down. Love this beastie.

Engine will occasionally and randomly hesitate, as in acceleration is, out of the blue, next to nothing , followed by brief but pronounced bucking as if I can't drive standard. Forcing gas it makes it worse, backing off helps. Lasts maybe a minute or two, then totally normal. Otherwise drives awesome. No seen pattern as to when it happens, does not seem associated with cold.If anything it is more when warm, possibly after idling for while. From other posts and research sort of sounds like a vacuum leak?

thnx
jeepgal

Sounds kind of like when I had a bad fuel pump, but I'd imagine it could be a multitude of things. My pump even had good pressure when tested, and was pretty random in its foul ups. Way I found out it was the pump for sure is when it would start acting up I pulled over and turned jeep off, then turned it to run position 3 times before restarting and the problem went away, at least temporarily. Might be something to look into but it could definitely be another issue entirely.

I had the same problem 3 days ago in my Cherokee 1996, 4.0L, 4x4. I changed the fuel pump, filter and washed the fuel tank. After that, everythng is OK. I spent half day with a friend.

i have the same problem but it is with an auto. i changed the pump, filter, pressure regulator. still same problem. today totally stoped running. when i try to start it it barley runs then dies. i have fuel pressure. stumped?

how does it idle? does it ever happen when you are coming to a stop or only when your taking off?

i've heard of that kind of thing happening when braking due to the torque converter going bad

Sounds like either a fuel pump going bad or an ignition coil going bad to me. You can do the fuel pressure check at the injection rail test port to test your fuel pump pressure. You can also take your igntion coil and ignition module down to your friendly local Autozone or Schucks to have them tested on there test set for free. If you need step by step instructions on how to do the fuel pump pressure test just let me know. You can also pick up a Haynes manual for XJs. The fuel pump test procedures are in there.

Buck

the pump pressure is good and i just put a new coil pack in. i checked for spark and it is good. it was only bucking on ecel then it was fine if i babyed it there was no prob. now if i get it to start it will barley run. i think its the crank position sensor. but im not sure on how to check it. i have no computer codes. i have a yj. its a 94 cherokee 4.0 2wd auto

Not sure if this will help you, but my buddies 99 did kind of the same thing except his would run better if he could get the rpms over 3k. After swapping everything his problem ended up being the 02 sensor.

My jeep is doing the same thing ... randomly, when accelerting ... I hold the gas steady, but the jeep actually slows down even in RPMs ... then after seems like 2-3-4 seconds, it "lurches" forward and the cycle repeats again.

It feels kind of like when you try to start from a dead-stop - in 3rd gear or something. complete lack of power

If I let off the gas, it "goes away" ... but of course, I'm decelerating which isnt good when trying to drive up a hill.

One thing odd though, if I get it up to 3k RPMs -- it "jumps" alive and cruises along with no hesitation problems.

And it seems to be much worse, if I don't let it warm up before driving.

I'm thinking maybe I have vacuum leak or possibly O2 sensor issue?

Some history on what I've tried:
* just replaces all (6) fuel injectors with new (4) hole kinds (thought it might help, but problem more frequent now)
* replaced coil with aftermarket one last fall, forget the name but it allowed the plugs to use a wider gap ... and added some power. (but didnt cure the issue)
* engine was complete rebuilt 2006 - still no oil leaks, etc. But so far I've replaced the following; TPS, CPS (crank sensor), (4) Fuel Pumps, (1) Water Pump plus the usual tune-up stuff ... plugs, plug wires (high temp kind, came with new ignition coil), filters, etc.

If not for this hesitation, I'd be driving this Jeep every day ... I love it.

But it hesitated and even stalled out while trying to 4x4 up a steep hill the other day ... and did this hesitation thing for about 10m today while driving into work

Gets bad enough my wife is now afraid to drive the Jeep ...

Please let me know if any suggestions / ideas on how to troubleshoot this issue are appreciated!!

ive pretty much got the same problem, i have a cracked header and im leaning towards the o2 sensor since that makes it run rich is prolly fouled out or something idno.

I'd try 02 sensor.

There aren't torque converters in manual transmissions, so it can't be that

Mine does the same thing. It did it a lot more when my O2 sensor was missing. I put an O2 in from the junkyard and it only did it twice in a one month period as opposed to at least 5 times a week before the O2 was installed. My O2 got ripped out the other day and it does it again and has NO *****! Can't even use 5th gear right now, because it bogs too much even at 70 MPH.

ordered a replacement o2 sensor but meanwhile tried filling the tank with premium gas and didn't notice any problems on the way home. Not sure if it helps, but thought it ought to burn cleaner ... Will let you all know if O2 fixes the issues. And thanks for all the responses.

I had a saturn that would do this. Went through all the stuff, spark, coil, pump, etc... Everything check. It turned out to be a couple bad spark plug wires, that would lose connection on acceleration.

Hey 96Cherokee113 -

My transmission is a 5 speed as well ... and has same problem as you describe. The more I read on the O2 sensor, more sounds like the cause of all the issues.

But I'm surprised that it doesn't generate an "O2 sensor" alert or something enough to create check engine codes. But I'm sure if you unplug it -- then you get the check engine light coming on.