4.0 help

ive got 93 xj 4.0 auto it idles fine but under acceleration it pops and runs rough like the timing is off ive tested all the sensors and they are good it isnt reading any codes and has good constant fule pressure i cant think of anything else to check the only thing left that i can think of is the computer itself i asked the stealership and they said if it was bad then you would get a code for it so i have no idea what to do next

tia,


trey

I would check your cat converter it might be plugged.
Lenny


trey[/QUOTE]

I seem to recall reading on other posts long ago by "Rags," the Jeep tech (where is he these days anyway?) that the coils on these could be problematic, and that sometime after 93 they beefed up the coil. Anyway, it sounds a little like an ignition problem, and I think the first thing I'd do is check the plug wires and the cap (try doing it at night and look for flashes), and perhaps have the coil looked at.

i agree withe lennyd...try the cat first..also have you checked the tps?..it contols alot of funtions. i have only needed to replace a computer once, and i have sold alot of cherokees a used one ran $395 installed. do you have a reliable idependant shop in the area?

arsonlvr said:

ive got 93 xj 4.0 auto it idles fine but under acceleration it pops and runs rough like the timing is off ive tested all the sensors and they are good it isnt reading any codes and has good constant fule pressure i cant think of anything else to check the only thing left that i can think of is the computer itself i asked the stealership and they said if it was bad then you would get a code for it so i have no idea what to do next

tia,


trey

Click to expand...

I just recently had the same problem.I did all I could think of and finally took it to a good repair shop that I deal with.They worked on it for 3 days and it really had them stumped.They finally came up with a tsb from Chrysler about
indexing the dist. They called it ignition crossfire/modify distributor.I dont know if thats your problem but its worth checking out.Do a search on indexing the distributor.There have been several posts on it in the past. Hope that helps.

I would definatley check the ignition system, just sounds like your not getting enough fire in the upper RPM range. good luck

I did some checking and I think this is the one that they are talking about.

NO: 08-35-93
SUBJECT: No Start, Hard Starting or Poor Performance
DATE: Aug. 13, 1993
NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0l ENGINE AND A 42 RE TRANSMISSION BUILT BEFORE MDH 05-28-XX.

SYMPTOM/CONDITION:
No start, hard starting or poor engine performance caused by internal shorting of the secondary winding of the ignition coil.

DIAGNOSIS:
If the vehicle exhibits any of the symptoms described above and is within the build date range, perform the repair procedure.

PARTS REQUIRED:
Quantity
Description
Part No.

1

Ignition Coil
4762312

1

Harness package
4762311



REPAIR PROCEDURE:
This bulletin involves installing a low resistance ignition coil and a jumper harness which contains an external resistor.

Disconnect the negative battery cable.
Disconnect the secondary and primary wiring from the ignition coil.
Remove and discard the ignition coil.
Install the ignition coil, P/N 4762312, and the secondary wire.
Remove the ignition coil insulator from the harness. Install the insulator, wedge and seal supplied in the harness package.
Install the jumper harness. Loop it toward the battery and tie strap it to the battery harness.
Connect the negative battery cable



Hope that helps
Lenny

I had pretty much the same thing awhile back. Started missing, bucking, wouldn´t accelerate. Decided to check the easy stuff first, found a loose spark plug boot, the hard way, with my fingure, hair raising experience. :scared: Changed my shorts, Replaced the cable, cured the problem.

Had a similar situation with my 89'XJ 3 days after I drove it off the lot(bought used,as is @4yrs ago)Damn thing acted like it was possessed.
Would idle perfect,BUT,if you turned on the turn signals,or the flashers,or anything electrical the vehicle would actually rock from side to side.
Took it to a local garage,they called me 1 day later said it was the control module(ECU) With a tune up and the ECU,cost me$800+change to get it back on the road.

Quite a few people have had this problem lately. "Most" of us have found problems with the fuel systems. On mine it was a loose hose clamp on the rubber line from the pump to the metal line in the tank. A few others had this same thing happen. It cured mine.

It won't show a code, and the only way to test with a pressure guage, is to drive it. It won't show up under idle conditions. I used my code scanner, and found that it was going extremely lean under hard accelleration, causing the backfiring in the intake, and loss of power up to around 2500 RPM's.

Might be a direction to go, and check out.