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View Full Version : XJ hesitation, stumbling, missing, spitting on acceleration and deceleration.


Jeepngdave
July 16th, 2010, 09:20
A couple of days ago My 96 cherokee sport with 4.0 engine and auto transmission started stumbling, hesitating, missing and when I give it more gas, spits or backfires before accelerating.
:dunno:It does not do it all the time. Mainly it does it after taking off from a standing start or before, during or after the transmission shifts from 1st to 2nd or 2nd to 3rd gear. The first time it did it was after I made a hard left hand U turn and it did it a couple of more times on the way home. I checked the ignition timing with a timing lite when I got home and it was ok but the mark on the fly wheel varies about 2 degrees everytime the light flashes.
I performed the shade tree fuel pressure test and gas shoots out the valve on the fuel rail when I depress the valve with the key on. I don't have a fuel pressure gague to check the psi. I replaced the fuel filter yesterday even though it was only about a year and a half old and there's no change.
About a month ago I replaced the CPS which cured a no-crank no-start problem. I checked all the emission sensors and ignition coil at that time and they all checked ok and I replaced the distributer cap and rotor also.
The jeep starts easily on the first try but these stumble/hesitation/misfire/spitting episodes are getting more frequent.
Ocassionally, when I'm comming to a stop, the engine misfires and acts like its going to die and it feels like the transmission doesn't down shift into a lower gear until I've come to a complete stop. Then, the engine is sluggish when I take off and if I give it more throttle the engine hesitates, then there is a spitting noise like my old chevy used to make when the accelorator pump in the carburator was worn out. Once past the hesitation and spit the engine accelerates normally.
Has anyone out there had or heard of a similar experiance and can suguest where I can start looking to correct this problem?

vabch87xj
July 16th, 2010, 10:15
i had a problem with the pick up tube connected to the end of the fuel pump

Jeepngdave
July 16th, 2010, 10:42
:wow: Thanks for your reply. :doh: Did you have similar symptoms to the ones that I'm having, and if so, how did you correct the problem?

wheelinscott
July 16th, 2010, 10:51
When I read this the tps came to mind, I believe I had the same problem years ago and iirc it was my tps

Tim_MN
July 16th, 2010, 11:34
The left turn thing is often the fuel pick-up tube or a wire harness issue. Inspect the wire harnesses for loose or dirty connections and for chafed insulation or melted insulation.

The missing and spitting can the the TPS, the Coolant Temperature Sensor (CTS), or a lazy O2 sensor. Inspect the wires for each and then test the sensors.

Can we assume that all of your tune-up parts are fresh and that you use some fuel injector cleaner 2-3 time per year ?

Jeepngdave
July 16th, 2010, 19:12
Tim_mn & Wheelinscott,

I spent a while this AM going through related threads and read that the throttle position sensor was a possibility also. So, I checked it with my digital meter and it checked low voltage. On my way to auto zone to purchase a new one the check engine lite came on for the first time so I double backed to the house and checked the code with my code reader and it came up Low tps voltage. The engine ran rough all the time now and spit, sputtered and stumbled the whole 6 blocks to auto zone and back.
I installed the new one and it ran fine for a couple of miles, then, stumbled and hesitated when I was decelerating to make a stop. Although it has an auto transmission, it feels like forgetting to down shift with a standard transmission when slowing down to make a stop or turn. The engine started stumbling and spit/backfired and then rpm picked up as I pulled away from the stop the third time it started stumbling/hesitating after slowing for a turn or stop.
After the engine cooled off I took it for a mile test drive and it did the same thing at the first intersection I came too with the engine not warmed up to operation temperature. While decelerating for a stop, it starts stumbling at slightly above idle. It has the stopping in too high a gear feel. Upon take off, hesitation, then backfire, then acceleration. It did the stumble hesitation again a couple of more times before I got back home. (It didn't make any difference which way I turned or if I went straight ahead after making a stop, I could tell when decelerating before comming to a complete stop by the engine starting to stumble most of the time if it was going to do the hesitation/spit backfire thing when taking off.)
So the TPS was part of the problem I believe. Service engine lite has not came back on but it didn't come on until I checked the tps and the voltage checked low a couple of times. My repair manual says connect the neg. test lead to the black wire, mine is blue with a black stripe so I checked it a couple of times to make sure I was testing the right wire. I don't know if my poking the meter probes in the back of the tps plug when I checked it has damaged the plug or I may not have the throttle body shaft inserted into the tps properly or......
Another possibility the I came acrost in the threads today was a worn distributer. I pulled the cap and the rotor will turn about a 1/4 inch when I try to turn it. The distributer shaft has about 1/4 in horizontal play when I try to move it from side to side and about the same amount of verticle play when I pull the shaft up and down. Does anyone know how much play is too much in the distributer? And can anyone tell me how to check the distributer pickup coil (camshaft position sensor)?
I checked the coolant sensor and mat sensor today also and they checked ok, but the the cps sensor checked ok with the meter last month when I had the turns over, no start problem and it was dead as a hammer. The engine started first try when I replace it with a new one.
All the tune up parts I purchased new at auto zone or O'Rellie's. I have not rechecked the coil or other sensors (O2, map, knock). They all tested good last month, but then so did the tps. (My test meter is new, I had to replace it when the old one died on me last month). Again, thanks for the advice. I believe that I've solved one piece of the puzzle. If you have any suguestions as to what I can try next your advice will be greatly appreciated.

Many Thanks!;)

Jeepngdave

joe_peters
July 16th, 2010, 19:51
Any side play in the distributor shaft is not good. It is supposed to spin concentric to the center line of the shaft--sideways play isn't good. Up down movement is Ok, but it sounds like you are ready for a new distributor.

When you need to back probe connectors, use a small paper clip with one leg straightened--you can knock the sharp edges of the end down a little with a file, no need to sharpen it.

Portuga_XJ
July 17th, 2010, 10:58
check your fuel pressure. mine did the same thing, problem was the fuel pump. changed it and runs like a dream now.

Jeepngdave
July 19th, 2010, 13:56
Thanks guys for all the great suguestions. I rechecked all the sending units and while I had the conectors off, cleaned them with electrical contact cleaner. The connector for the front O2 sensor has the plastic lock broken off and it was just barely plugged in. After reconnecting it I went for a test drive and engine runs fine.
So, I took it out on the innerstate up to 75 and then around town including some hard left and right u-turns in a couple of parking lots to try to recreate the event that occured right before the problem started and still no stumble/hesitation/spit/backfire.
I purchased a fuel pressure gague today so I can check the fuel pressure and I'm planning on replacing the worn distributer in the near future.
I believe that the TPS and loose O2 sensor plug were the immediate problems. :listenmus Many thanks again guys and happy trails! Now, do any of you guys know anything about british motorcycles? I'm having a devil of a time getting my triumph 650 motorcycle to run right. I seems to have an air leak in the amal 930 carburators causing lean running in the idle circit and I've checked all the usual suspects (leaking carb mounting flange, & pilot jet pathway is clear) Any ideas?

cheddarpecker
July 21st, 2010, 18:23
Thanks guys for all the great suguestions. I rechecked all the sending units and while I had the conectors off, cleaned them with electrical contact cleaner. The connector for the front O2 sensor has the plastic lock broken off and it was just barely plugged in. After reconnecting it I went for a test drive and engine runs fine.
So, I took it out on the innerstate up to 75 and then around town including some hard left and right u-turns in a couple of parking lots to try to recreate the event that occured right before the problem started and still no stumble/hesitation/spit/backfire.
I purchased a fuel pressure gague today so I can check the fuel pressure and I'm planning on replacing the worn distributer in the near future.
I believe that the TPS and loose O2 sensor plug were the immediate problems. :listenmus Many thanks again guys and happy trails! Now, do any of you guys know anything about british motorcycles? I'm having a devil of a time getting my triumph 650 motorcycle to run right. I seems to have an air leak in the amal 930 carburators causing lean running in the idle circit and I've checked all the usual suspects (leaking carb mounting flange, & pilot jet pathway is clear) Any ideas?

Replace with Mikunis. That's what all the old folks told me. Had an amal on my 69 bultaco, mikuni on my 74, big difference considering they were both Alpina 350s.