Hesitation/bucking on acceleration??
04-22-2019, 11:54 PM
#61
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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!!
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!!
04-23-2019, 12:02 AM
#62
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Wanted to bump this thread. I think there should be a sticky about fuel pump failure symptoms. Not all are the same, I understand, but this symptom has happened to me and I wasted $1500 between Midas failing to diagnose the problem correctly, and then biting the bullet and having the dealer diagnose and replace the fuel pump. I now have a 1999 and just started doing this tonight. Here are the symptoms I experienced tonight, and two years ago:
1. Severe bucking on acceleration, just like jenz said about it feeling like its a straight drive and you don't know how to let off the clutch.
2. Let off the gas and it seems to pick back up, but very weak throttle.
3. Often times it completely dies, and I sit on the side of the road for about 20 min, start it back up, drive for maybe 15 or 20 min, dies, rinse and repeat.
4. Will not immediately re-start after it dies on the road.
5. Feels like the more pedal you give it, the worse it dies. Makes sense cause when you open the throttle and give it more air with no gas, it leans it out to thin and dies.
So tonight my 1999 started acting up on the way home. Same exact symptoms. I just barely coasted it in to the drive way when it finally gave it up compeltely. Could not get it to restart. I was thinking maybe the gas gauge was stuck, and I was out of gas. I dumped a 5 gal can in that I keep for emergencies, and still not start. It would turn over, grumble a bit, then die. I waited 30 min. Went back out, started right up. I heard a very soft high pitched whine coming from the fuel tank. Sounded like the fly-back transformer in an old CRT television. If you have heard that ringing sound you know what I mean. Anyway, just as a hoot I decided to bang on the bottom of the tank with my fist. The jeep immediately died. I started it back up no problem. Still hearing the high pitch whine that I suppose is a bearing in the fuel pump that has given up its spirit. So I am going to go get a fuel pump tomorrow or the next day when I get time ( i am a full time Soldier with little disposable freetime) and will post back my results. I'm betting I am right in my diagnosis. Anybody want to bet against me?
EDIT: By the way, I wanted to tell you all that when the dealer and Midas both checked the fuel pressure, it was just fine. The only way they caught it was when the dealer was getting ready to do a distributor test, he noticed the fuel pump voltage acting flaky. This was an Autozone spectra fuel pump that was 1 year old. So, I bought a Delphi fuel pump from NAPA and gave it to the dealer to install cause I was not going to pay dealer prices. It was dead on arrival. Got another one from Autozone. Again, dead on arrival. Finally got a Precision fuel pump from Orielly's, and it has been going strong for 2 years now. Don't think just cause you replaced the fuel pump recently that your problem cant be a fuel pump. I wasted $1500 on this flawed assumption.
1. Severe bucking on acceleration, just like jenz said about it feeling like its a straight drive and you don't know how to let off the clutch.
2. Let off the gas and it seems to pick back up, but very weak throttle.
3. Often times it completely dies, and I sit on the side of the road for about 20 min, start it back up, drive for maybe 15 or 20 min, dies, rinse and repeat.
4. Will not immediately re-start after it dies on the road.
5. Feels like the more pedal you give it, the worse it dies. Makes sense cause when you open the throttle and give it more air with no gas, it leans it out to thin and dies.
So tonight my 1999 started acting up on the way home. Same exact symptoms. I just barely coasted it in to the drive way when it finally gave it up compeltely. Could not get it to restart. I was thinking maybe the gas gauge was stuck, and I was out of gas. I dumped a 5 gal can in that I keep for emergencies, and still not start. It would turn over, grumble a bit, then die. I waited 30 min. Went back out, started right up. I heard a very soft high pitched whine coming from the fuel tank. Sounded like the fly-back transformer in an old CRT television. If you have heard that ringing sound you know what I mean. Anyway, just as a hoot I decided to bang on the bottom of the tank with my fist. The jeep immediately died. I started it back up no problem. Still hearing the high pitch whine that I suppose is a bearing in the fuel pump that has given up its spirit. So I am going to go get a fuel pump tomorrow or the next day when I get time ( i am a full time Soldier with little disposable freetime) and will post back my results. I'm betting I am right in my diagnosis. Anybody want to bet against me?
EDIT: By the way, I wanted to tell you all that when the dealer and Midas both checked the fuel pressure, it was just fine. The only way they caught it was when the dealer was getting ready to do a distributor test, he noticed the fuel pump voltage acting flaky. This was an Autozone spectra fuel pump that was 1 year old. So, I bought a Delphi fuel pump from NAPA and gave it to the dealer to install cause I was not going to pay dealer prices. It was dead on arrival. Got another one from Autozone. Again, dead on arrival. Finally got a Precision fuel pump from Orielly's, and it has been going strong for 2 years now. Don't think just cause you replaced the fuel pump recently that your problem cant be a fuel pump. I wasted $1500 on this flawed assumption.
09-30-2019, 10:54 PM
#63
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Did you try a new gas cap?? Perhaps yours is not venting properly.. today I just changed out my fuel pump/in tank filter and pressure regulator (it was all one unit) I hope mine stops bucking process of elimination I will get a gas cap next. UPDATE!!!! I changed my fuel pump, filter , pressure regulator combination in My fuel tank and found that my inlet screen fell off my old pump in the tank. NO MORE BUCKING
Last edited by MR THE KATT; 10-03-2019 at 01:32 AM.
10-01-2019, 01:21 AM
#64
Hesitation/bucking on acceleration.
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
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
I have a 2004 Jeep Grand Cherokee 4.0 in line 6 cylinder and mine was doing the same exact thing. I ran 3 or 4 bottles of fuel injector cleaner through it and once I used Chevron Theron fuel treatment and injector cleaner it stopped all together. Also ran high octane gas with Lucas in it constantly. Now it's perfect. I personally think your injectors are clogged. Now that's what mine did and it worked. Also did oil change, changed spark plugs. Chevron Techron worked the best!!! Can't hurt to try. And when your car starts bucking let off gas.
10-03-2019, 01:23 AM
#65
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Update!!! No more bucking
99 XJ Cherokee sport 4.0 automatic 4X4........ So I started with changing the spark plugs, then I tried changing the coil , then I changed the front and rear o2 sensors Then I changed the Fuel pump filter and regulator unit in the tank from O’reilly , I took it on the freeway and tried to make it hesitate and buck but it never did,,I think it’s fixed!! Thank you all for your posts, my problem is solved for now. Good luck everyone
11-01-2021, 06:37 PM
#66
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12-16-2021, 12:41 PM
#67
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This thread has been really helpful in helping me wrap my mind around possible causes for my hesitation issues with my 98 XJ automatic. Similar to others, mine will happen intermittently (some days not at all, some days once or twice during a days drive). It NEVER happens on the first drive of the day, first thing in the morning. So far it has always happened after I've driven it on that same day. BUT it does hesitate usually right after I first start it up. The RPMs go flat despite mashing the gas pedal, and this usually only occurs for a few seconds or less (I've learned to take my foot off the gas and re-apply, which usually helps). Hesitation typically occurs in 1st gear, once in 2nd. This all sounds like what others have described.
I recently purchased the truck, and the seller told me he was getting a p0171 code previously, but I have yet to see a check engine light. Initially it was idling erratically, but a new TPS and IAC valve seem to have fixed idle issues. I haven't seen anyone reference this specific OBDii code yet in this thread, so through I would mention it.
Only has 120k miles on it, so hopefully it isn't as involved as a fuel pump issue, but sounds like it could be. This weekend I plan to change both o2 sensory and check all spark plugs. If that doesn't fix it, my next step is to look at possible ignition coil or MAP sensor failure. Then to the fuel filter (hopefully it won't be necessary, really don't want to mess that that).
I know this is an old thread now, but it has been really helpful to me as a new Jeeper, just wanted to share my gratitude.
I recently purchased the truck, and the seller told me he was getting a p0171 code previously, but I have yet to see a check engine light. Initially it was idling erratically, but a new TPS and IAC valve seem to have fixed idle issues. I haven't seen anyone reference this specific OBDii code yet in this thread, so through I would mention it.
Only has 120k miles on it, so hopefully it isn't as involved as a fuel pump issue, but sounds like it could be. This weekend I plan to change both o2 sensory and check all spark plugs. If that doesn't fix it, my next step is to look at possible ignition coil or MAP sensor failure. Then to the fuel filter (hopefully it won't be necessary, really don't want to mess that that).
I know this is an old thread now, but it has been really helpful to me as a new Jeeper, just wanted to share my gratitude.
Last edited by jallen9339; 12-16-2021 at 12:45 PM.
01-04-2022, 08:16 AM
#68
Newbie
*UPDATE*
Since installing two new O2 sensory, I have not had any hesitation issues. I think the particular culprit for me was the upstream O2 sensor (the one closest to the exhaust manifold).
Since installing two new O2 sensory, I have not had any hesitation issues. I think the particular culprit for me was the upstream O2 sensor (the one closest to the exhaust manifold).
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