Hi all. I have searched this and am still stumped.I have a 1996 jeep cherokee 4.0L6 with the warner trans.It has a issue that I cannot figure out. It starts fine every time but completely randomly it will have a spell where it runs rough (very rough) and then it is gone.Basically you are driving down the road fine and then all of a sudden someone flips on a run like crap switch then after a little while it clears up and runs perfect again. (like it never even did it). Maybe It is just me but it almost seems to me that it is running very rich when this problem occurs, but after the spell it is fine.No starting issues.When it does it it has very little power, almost stalls completely sometimes.I have replaced plugs, wires, distributor cap, rotor, pickup, CTS, IAC, both oxygen sensors, oil pressure switch, fuel filter, I have checked the fuel pressure several times and it is spot on, but I can never get it to act up when I have my gauge hooked up. The other day I had it running in the garage and the spell occured but I did not have my gauge on me.There is no light or codes. I check it often hoping something would throw a code. When it runs fine it is perfect. Any insight is highly appreciated as I am very stumped. I am not wanting to keep throwing parts at it.thanks in advance
96 Jeep Cherokee runs fine then rough, then fine
- Thread starter rockfangd
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- 4.0 engine issue running rough
desertrunner
New member
And your gas tank is clean as well? It's possible every now and then crappy denser fuel or liquid that's sitting on the bottom of the tank makes it in your fuel lines...
desertrunner
New member
It may be a bad connection on ur fuel pump... Or a bad fuel pump.. if it stops working for a few seconds and the pressure dies out it would run awefully until the pressure is gone and it would stop running...
jpatterson
New member
try this, when the jeep is running and hood open use a flashlight to tap on the ecm if it runs like crap then clean and reconnect the harness use zip ties to secure the plugs so they do not rattle. if it still runs funny after the zipties when you tap the ecm the ecm may be faulty.
brandonmed
New member
I had the same problem with my 98 wrangler 4.0. Used to drive me crazy. I also owned a 98 grand cherokee with the 4.0 so I sat in the driveway swapping parts like map sensors and things. Never could figure it out. Such a random occurrence. So I ended up just trading it in. I still have the grand cherokee till this day though. Lol. Good luck!
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98Chero
New member
had the same problem with my 96 4.0. I let the engine run while I jiggled the wires around the intake and found a wire that was barely making a connection on a quick connect. repaired the bad wire by removing the quick connect and wiring it direct. hope that makes sense.. but it fixed the problem.
I hope this helps
I hope this helps
Hi all. Just wanted to share. Jeep is still having problem with run like shit switch, It does throw a catalyst efficiency cody sometimes so I am thinking replacing the cat and hoping for the best. I already replaced both o2 sensors to try to cure the code but neither helped or resolved the problem.
greg92jeepxj
Official Supporter
Sorry to hear you still have this intermittent problem. I guess cleaning PCM connections and securing wiring harness connections to PCM did not help ? If you are suspecting PCM problems , search for this thread on our forum using search feature ; member DRAGON 5126 jeep PCM issues date 9/5/12 . You will find it interesting and hope it helps you. Incidentally , have you checked MAP sensor ? Although a code did not set for MAP , make certain vacuum line is tight and does not leak. One more thing to ask , is the charcoal canister possibly loaded with raw fuel ? You mentioned that you believe you have a rich condition . If purge valve sticks open at any time , engine will run overly rich. Also check vapor return line from fuel tank is not carbon blocked . In carbureted engines , this caused fuel pumps with vapor return lines to interrupt fuel pressure . At 5-7 psi, didn't take much to cause loss of power or carb to run low and cause engine miss. In a MPFI system , this may cause fuel pressure regulator fuel return to tank to back up and create a block in fuel rail momentarily . I helped correct a clogged return line on a 1990 jeep XJ 4.0 by blowing out return line with compressed air . This seemed to help as the jeep had a cleaner idle and did not loose power or miss on acceleration or threaten to stall.
One more item ; see if your oil pressure sending unit switch has a leak . If this unit looses enough pressure , it will trigger auto shut down relay. Without spending money , these are more items to check. Best of luck . It is better to check the PCM this way before condemning it with the member's post on PCM repair at home . It's always a good idea to check vacuum lines . I found the rear vacuum line going to the crankcase breather leaking at valve cover connection .
greg92jeepxj
Official Supporter
Your welcome . As always , when you can , post your findings and most certainly let us know when yor jeep is cured . We are always interested for our edification . There are always members and guests that research as we all do for trouble shooting tips and you may just end up being their hero ! Thanks and best of luck . Greg
GreatWhiteCherokee
New member
I had same thing. Took out PCM n soldered headers back on chip. Then seafoam in gas tank, drive around, hen change fuel filter. Then took it to Midas and got new cam sensor, distributor, and rotor. Problem solved
Ok all. I have 2 things. I bought a used ecm from a jeep with the same year and engine, not sure if the trans is the same
I have a few questions
What other than the engine is controlled with the ecm? basically I am wondering if they are different between 4x2 and 4x4 models
and same going gor the 2 transmissions offered.
I also think I should get a crank sensor while I am at it. The jeep has been doing it so randomly it is driving me nuts..
I would like to repair the ecm I just got and install it but I dont want to break the seal and void the warranty and get stuck with a useless ecm. Thanks all
I have a few questions
What other than the engine is controlled with the ecm? basically I am wondering if they are different between 4x2 and 4x4 models
and same going gor the 2 transmissions offered.
I also think I should get a crank sensor while I am at it. The jeep has been doing it so randomly it is driving me nuts..
I would like to repair the ecm I just got and install it but I dont want to break the seal and void the warranty and get stuck with a useless ecm. Thanks all
greg92jeepxj
Official Supporter
The label on the PCM has a service number , do they match ? The PCM primarily manages the engine , a separate module , usually found under the dash on the XJ , manages the transmission solenoids. The salvage PCM needs repair ? For what reason ? BTW , a 90's era and later on board computer is referred to , by the manufacturer , as a power train control module , which is the engine. Chrysler actually calls it an engine controller. An ecm is an 80's era electronic control module. They ran electronic carburetors , TBI units ( throttle body injection ) and early MPFI ( multi port fuel injection ) before the sequential port fuel injection era started. Would like to know why you need to repair a PCM that was purchased for replacing the existing PCM . The service numbers are important , they are the vin number of the engine management system . They are specific to fuel delivery , ignition , and emmissions control. To be more specific , what do you feel is wrong with the current PCM ? I know you have this intermittant drivability problem but you also mentioned you may suspect the CPS , which is a good place to start . Do the repair manual check to the sensor and circuit first , I believe that all else should be exhausted before PCM replacement. All checks that is. If there should be an open ( short to ground for example ) , a replacement PCM will be damaged .
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