98XJ"Blue"

Hello,

I am having a problem with my XJ bucking and popping while driving and sometimes while idling. It struggles to start but I found that going key on and then starting helps it fire up but if you let it idle or start driving, within 10 minutes the revs will hang for a second and then crash and run really rough. Hitting the gas doesn't accelerate the car and if you stomp it it will pop a bunch. It feels like there is a bubble under the gas pedal when this is all happening. If you pull over and stop while its doing this the engine will buck and surge. The part that really confuses me is that it will do it once per drive anywhere. Once it throws a fit and recovers it won't do it again for the remainder of the trip until I turn it off and start it up again later. The check engine light is on but it is only for evap codes that were there before this ever happened.

Any help is appreciated as its my only form of transportation and I am really growing worried that its going to leave me stranded somewhere soon. I'd be happy to explain further if this post wasn't clear.

Thanks.

PatHenry

Check your fuel pressure. You can rent the tester at your local Autozone or other parts store. You're looking for a solid and steady 49.2psi +-5.
If it's not within that spec, you probably need to replace the fuel pump. Your symptoms are very much in line with a fuel pump that is dying.

98XJ"Blue"

I had a suspicion that it was fuel related and I will definitely test it out, thank you. Do you have any explanation as to why it only acts up once per trip though? If it was a failing fuel pump why does it all of the sudden act perfectly for hours of driving after it freaks out once?

PatHenry

Well, you don't know that it's fuel related or not, yet. The fuel pressure test will tell you if the pump is working correctly. Some other things you should check would be engine grounds. Make sure all the grounds are clean and tight. There are two in the trunk on the driver's side behind the trim panel that are often overlooked.
You could also check that your throttle body is clean.

IF it is the pump, it could have trouble getting up to pressure and once going is ok..

MonacaYankee

My 1994 Cherokee had your symptoms when it needed a cap and rotor and the middle plug on the cap going to the ignition coil had corrosion on it.

Could also be your o2 sensor. My 99 would hesitate and the backfire once and be fine after that backfire. It did not have your other symptoms though.

PatHenry

Also double check that there are no new codes.

Garon Keaton

Is your check engine light on?

98XJ"Blue"

I had the cap and rotor replaced recently so I know its not that. Is there a way to test and see if its the O2 sensor?

ThefubarJeep

Hey!

Did you find a resolution to this? I also have a '98 that is doing the EXACT same thing. Drives and shifts just fine, then throws a fit, always in the first 2 minutes of driving. Popping can be felt under the gas pedal, wont accelerate, bucks, then recovers and drives fine again.

I went under the hood and cleaned grounds, all electrical connections I could find, greased all the connectors, I know my throttle body is clean, can't figure this one out.

No check engine light, no other symptoms.

BlueRidgeMark

Check your fuel pressure, as suggested above.

Then check the wire going into the coil. Sometimes that connection is loose.

ThefubarJeep

Fuel pressure is fine, coil wire is fine, only bucks when in D, throw it into N and it revs just fine.

OP, did you ever get a solution to this?

awg

You suspect if he was gonna speak he would have done so by now, being that its nearly 2yrs now

you always wonder, did they just give up and send it to the junkyard, sell it as a non-goer, or just couldnt be bothered updating

if your crank sensor is very old, it would be a possible suspect item

98XJ"Blue"

I did find a solution and it turned out to be the O2 sensors and based on your description I'm willing to bet yours are also the problem too.

The way I found out mine were bad was my code reader will actually let me see a live data stream of the car running so I could see various stats about the engine. The important stat that i could see was whether the engine was in closed loop or open loop. When you first fire up the engine it starts in open loop which means it's not taking any feedback from sensors like the O2 sensor. When it switches to closed loop, that's when it takes the feedback from stuff like the O2 sensor to manage the engines performance. What I was able to see with mine was the problem happened right at that point of switching from open to closed which told me it had to be sensor related.

Upon doing some research on O2 sensors, I learned that they have a heating element built into them that helps them get up to temp faster so when the engine switches from open to closed the sensor is in the right operating range to give accurate feedback. What happened in my case was that the heating elements weren't working so the engine was getting feedback from a cold O2 sensor which made the engine think it was running way out of AFR range and making it run like garbage until the O2 sensor got heated up by the exhaust gas alone. This was why it would only happen once a drive and in the beginning. The sensor itself was fine and that's why the engine would think its feedback was accurate but in reality it was the heating element that wasnt working. I think this is also why I never got any check engine codes.

In short, change your O2 sensors and i hope this helped.

99XJ4.0

I agree with 98XJ"blue" I have had two different XJs with this problem and it has always been the o2 sensors and it does not always trip the check engine light but don't buy the Bosch o2 sensors that most parts stores will try to sell you they won't last. I had a 98 that I was replacing the o2 sensors every six months until I bought replacements from the dealer and never had a problem after that. I have also had good luck with ntk replacements and you can find them online for a fraction of the price of the Mopar ones.

Morat

I find the torque app and a cheap Bluetooth OBDII adaptor really helpful with this sort of error. You can look at the live readings from the O2 sensors, see what the trims are set to and read/reset codes. (And loads of other stuff). It's super cheap for what it is. For 96 and up, of course.