[palidine556]

I have an 1991 Cherokee Sport 4.0L. When I rev it up to about 4000 rpm in drive or neutral, the motor cuts out then comes back. The revs jump from 4000 to 3000 very quickly and abrubtly about 4 times a second. The engine sounds like it is backfiring when this happens also. It always starts up and drives just fine other than that. It has full power up unitl this starts happening also. I have checked the fuel pressure when it does this and it is good. I removed the catalytic converter to see if it was clogged but it didn't affect it at all. I have replaced the following items to try an fix it:
TPS
Fuel Filter
Spark Plugs
Spark Plug Wires
Distributor Cap
Rotor
02 Sensor
I was told it could be the coil, but I would like some more educated guesses so that I am not just throwing more money at it. Can someone link me to how to test the rest of the sensors for a HO engine as I have not found any info on that subject.
Any help is greatly appreciated.

[Gsmyth75]

I have the same kind of problem, and I've replaced everything you have short of the o2 sensor.. Maybe it is coil or iac sensor.. Maybe someone else will chime in on this one.

[palidine556]

I bought a new coil for the jeep today and installed it, but still the same problem. Is it possible that I have a blown head gasket or slightly warped head that only leakes at full throttle? I don't have any idea what else it could be. Any help would be greatly appreciated.

[EagleStorm]

May be the rev limiter you shouldent be at 4000 rpm sitting still

[palidine556]

How would I go about determining if it is the rev limiter, and is it adjustable at all.

[compfreak530]

Have you checked your tps? iv read in another post were the person described problems like yours and they readjusted there tps and it cleared the idle up alot.

[collkid]

I'm interested

[EagleStorm]

the revl imiter is not adjustable how does it drive ? is it cutting out or is this just somthing you found out?
if it drives normal with out cutting out you dont have a problem if it cuts out while driving thats diff

[BrunoS]

strange..with new fuel filter, coil, should not be a problem.

check for any codes, truly could be a bad computer.

[Gsmyth75]

What about Map sensor? since a new one is only 40 bucks I'll do that and post any differences since i have the same problem.

[BrunoS]

jes us, pull codes with a obd scanner or key on/off trick....

replacing parts is not the option yet.

could be distributor sync pickup (below distributor rotor inside the cap) going out or spark/fuel issue, or plugged injectors....
pull codes first!!!!

[Gsmyth75]

My problem turned out to be map sensor.. hope that helps

[94XJCOUNTRY]

You may also check for airway restriction at higher rpm. A friend of mine was experiencing a similar condition on his 91 and found that his rubber intake tube was weak and collapsing at higher rpms. We were able to find this by reving it from under the hood and seeing the tube close up on itself. Some of the older jeeps also had a heat riser flap at the air intake in the front of the lower portion of the air filter box, I have also seen this cause the same type of a problem. Again, may or may not fix your problem, but could be a good place to start. Good luck with it!

[palidine556]

Update,
The intake tube was not collapsing on me, I checked the codes on with the key on/off trick and found nothing but 12 and 55 which is battery disconnected in the last 50 starts. I took it into the dealership to have them look at it, they adjusted the distributor cap and ran it through but it still didn't fix the problem, the tech said that he thought it could be a bad cps sensor that misses after high rpm or a cracked flywheel that is twisting under the load of high rpm. He said he believed it was a ignition issue since all the cylinders would go out and not just one. I wasn't going to pay them to drop the transmission to see if it was a cracked flywheel and i can change the cps myself for alot cheaper. He said that he hooked up the computer to it when he ran it though and the cps was still registering when the misfiring occurs but he thinks that it is telling the computer to fire at the wrong time. Does this sound reasonable? Cost me 230 bucks for the guy to tell me he didn't really know what was wrong but that was his best guess.

Also could anybody explain what the distributor sync pickup is?

List of parts replaced so far:
Wires
Plugs
Distributor 2X (by me and the dealership after I told them not to)
Rotor
Ignition Coil
Map Sensor
TPS Sensor

Also did the following:
Cut off catalytic converter
Ohm Tested Injectors-good
Checked fuel pressure when backfiring-Solid 40 psi
Ran fuel system cleaner though gas tank 2 times

[EagleStorm]

is the jeep running ok other than you jacking it to 4000 rpm at idle?????