87 XJ Jerking during accelleration, hard starting and stalling???

[csr_011]

Hello all! Im new to the forum and have been stressing over my favorite vehicle for some time now. I have a rebuilt 89 4.0L in my 87 Cherokee 4 door automatic 4x4. The old motor was shelled, could not be bored for rebuild.
The problem developed at about 3000 miles after the rebuild, almost seemed overnight. The whole thing would jerk when accelerating liek the drive train was going to drop out from under the vehicle, sometimes it would do it several consecutive times during acceleration at low speeds and passing on the highway. At almost the same time it developed a hard starting problem and stalling out on right turns and stopping at lights and stop signs, very tough to restart sometimes and sometimes would start right up after this. This weekend it did the usual stalling but then dieseled a bit afterwards, then when i restart it revs up to about 3000 RPMS! the EGR was not changed at the rebuild, was supposedly functional, not sure about the TPS or IAC. I have had it to a coupld mechanics and they find nothing wrong, one even drove it to and from work for 4 days and nothing happened! I desperately need some input as this is my baby and i want to finish the restoration. Its going ot be my hunting fishing vehicle, but not reliable enough now to trust on the long trips. I will be installing a 3 inch Rustys Off Road spring pack kit in a few weeks cause the suspension is almost shot, figured i might as well raise it a bit since i wanted new coils, shocks, and leaf packs in. Please help!!!
Cory

 

[csr_011]

Oh, the jerking is like the engine cuts out for a split second, but no lights on the dash or electricals go out when it does this.
Cory

 

[csr_011]

Sorry, one more thing, there is a new ignition module, coil, pickup coil, cap, rotor, plugs, wires, and all new vacuum at the rebuild.
Cory

 

[Ron Hyslop]

Check that the distributor is indexed properly. Mine came from the factory with the distributor installed one tooth off. There is a factory bulletan on the subject and probably a procedure here somewhere if you do a search.

 

[8Mud]

From the sound of things, you may have more than one thing going on. Couple of things to keep in mind, is below around 140-160, the computer doesn´t run off of all the sensors, so problems below 140 eliminate some possiblities.
The reving to 3000 or so sounds like the TPS. The TPS is a two part TPS, one side for the tranny and one for the motor ECU. Replacing the TPS, may be a waste of cash, mine turned out to be dirty (oily) connector. Checking and cleaning the grounds, by the dipstick brace is a good starting point. That´s where the TPS, the TCU and the ECU eventually gorund. First step anyway.
The stalling could be also be TPS related, how is your idle? To partially eliminate the EGR, you can plug the line between the EGR valve and the transducer. Mine had a weak spring, would open at a low vacume. Also possible the vacume solenoid for the EGR is bad, plugging the line will eliminate these two possiblities.
Vacume is always a question, new or not, things come unplugged or vacume lines get cut on sharp corners. Brake boosters leak and vacume resivoirs crack.
How deos your air filter look?

 

[Dr. Dyno]

The whole thing would jerk when accelerating liek the drive train was going to drop out from under the vehicle, sometimes it would do it several consecutive times during acceleration at low speeds and passing on the highway. At almost the same time it developed a hard starting problem and stalling out on right turns and stopping at lights and stop signs, very tough to restart sometimes and sometimes would start right up after this. This weekend it did the usual stalling but then dieseled a bit afterwards, then when i restart it revs up to about 3000 RPMS! the EGR was not changed at the rebuild, was supposedly functional, not sure about the TPS or IAC.

This sounds very much like your CPS is intermittently failing, so I think you should replace that as your first measure. The high idle after restarting could simply be caused by a dirty sticking IAC, so remove it from the TB and give it a good cleaning.

 

[jneary]

sounds like the distributor isnt indexed properly if it was removed and reinstalled. you may want to check out my response to the post by "fletch", that describes how to index it properly

 

[csr_011]

About the distributor, the engine builder, who is a jeep man himself for over 20 years installed the distributor. As i said, it ran fine for about a year, then slowly developed these problems.
thanks,
Cory

 

[csr_011]

CPS....Crank positioning sensor? or crankshaft sensor? or something else? The crank sensor was new at the rebuild, got an OEM one from the dodge dealership. That is the one that mounts on the tranny bell housing, let me know if that is what you are talking about.
Cory

 

[jneary]

crank sensor, cps, etc. its all the same

 

[csr_011]

oops, forgot one, the idle seems ok but could be smoother i believe, its up and down slightly, not a consistent rpm nor a very high or low idle. Vacuum leaks have been looked for, found two fixed them. There is a slight hissing when the brake is applied at stop signs though, thought maybe the booster is causing that somewhere, the fat vacuum line off the booster is not leaking, who knows
Cory

 

[jneary]

is it an automatic?

 

[Professor Bobo]

I'd try the Crank Position Sensor (CPS). Mine started out like it was cutting out for just a second. It eventually got worse. Check the resistance of the sensor or see if your Jeep man has a known good one he can lend you to see if it's the problem. (they cost about $50).
Just my opinion.

 

[csr_011]

Its an automatic, the CPS is good, replacing the TPS and IAC tuesday, hope that cures the hard starts and the cutting out, should smooth the idle out a bit.
Cory

 

[jneary]

i still would double check the distributor indexing.

 

[logdog]

TPS....mabey. More likely to be a failing fuel pressure regulator, or a bad injector. Pressure regulator or TPS for the "miss" while driving, and the injector for the starting problem. When you have a leaky injector, it will drip into the cylinder and flood the engine.

 

[csr_011]

we thought that maybe the #1 maybe misfiring or leaking or something, have to have that checked out when the new parts are on. Fuel pressure is fine at idle and when throttled, so i have been told by a mechanic. Thanks.
Cory

 

[csr_011]

OK, replaced the TPS and IAC, still having the jerking during acceleration and the dying on bumps, dips, and when coming to a stop sometimes, not all the time. Also i didnt set the TPS, forgot the multimeter, put it where i believe it was positioned before. The sitting idle is much smoother now, however it still starts rough. Going to pull some plugs tomorrow and see if there are any fouled due to a leaky injector or something. it almost has to be an electrical problem for the dying when slowing down, bumps, turning right, and stopping, not sure on teh cutting out part. Starting is also pretty rough. Sometimes it grabs on teh second crank, sometimes it takes about 10 cranks, have also pushed the TPS down with a screwdriver when cranking and it starts up. I am so lost............

Cory

 

[old_man]

Hissing when brake applied? Try a pair of vice grips on the vacuum hose to the booster and drive just a bit. Remember your brakes will be hard as heck to push to stop. I have seen more than one leaky brake booster cause tons of problems, but like the man says, sounds like more than one problem.

 

[jneary]

did you ever double check to see if the distributor was indexed properly. you didnt mention having this problem before installing the motor, so the engine components should be ok. to me it seems like something done when the motor was replaced.