Problem: Jeep stalls intermittently. Once warmed up and driven for about 20 to 30 minutes sometimes less it will either stall while driving or while idling. Sometimes it dies on initial start up during idling. Once it stalls it will run a bit rough an die usually within 2-5 minutes of restart. Other intermittent issues include on a cold start will run rough and die. This happens very rarely. The longest I have had it running and driving is about 30 minutes since I purchased it less than a month ago. NO CODES PRESENT
What I have done to try and fix the problem:
-Check fuel pressure: 50 PSI
-Fuel pressure leak down was 2 psi in 5 minutes
-new ignition coil
-alternator test good
-new battery
-clean and wire brushed battery connections
-cleaned battery ground to chassis
-clean IAC
-swapped cam sensor with a junkyard one to check if it was the issue
-new crank sensor (MOPAR)

Compression test within spec

From front

1-155 psi
2-160
3-150
4-160
5-150
6-160
-fixed a spark plug boot where connection had deepened and wasn’t making it to the plug
-reapplied dielectric grease to all the spark plug wire connections
-fixed vacuum connection that had come unattached from exhaust
-fixed vacuum leak at pcv valve
-swapped a good ECM from advance auto in same problem persisted. Swapped back old one
-new fuel filter
-installed new ground strap from head to chassis
-installed new coolant temp sensor (2wire)
-new plug wires
-new distributor cap and rotor



No luck with any of these repairs. Curious where I should go from here. I'm looking for anything else that maybe obvious that I am forgetting which could be causing my issues.

 

Year, make and model please, if not too much trouble.

 

engine?

 

Its located in the title. Just for reiteration 1996 grand cherokee laredo 4.0 I6 motor 242 ci. I have added updated information to thread as well.

 

Nobody wanted to help me. Thats cool. I figured it out so I figure I ll help the next person. I had to replace the connector on the far right on the computer. Cut it from a junkyard and spliced new one in. Also used two pieces of flat steel and two bolts to create a clamp on computer plugs. Jeep is fixed. Took me 1 month to figure out,

 

Hi Kyle, yes clearly a 96 ZJ with 4.0.
Appreciate the follow up! I've been chasing a so very similar misbehaviour on our 95 for a couple of years. Most prevalent when heated up, seemed like vapour lock, so similar, but all lines now insulated, and a 165 deg thermo did not solve the issue.
Seems to be some relationship with the temp sensor above the water pump, will go to default mode if I disconnect and allow me to restart when engine hot (hot, not overheated) and drive home.
I'll definitely check out the connector(s).
When you describe the "right" side, did you service the passenger side at fire wall or driver side by air box?
Good to hear your 96 is resolved.

 

I see these posts from time to time and they are difficult to trace out, which is why not many peaple responded (no one really knows the exact solution) Your approach was thorough and the details you provided will hopfully help somone else out. My first thought was computer, but then i saw you replaced it. It turned out to be the connecting plug, which is unusual and the first time i saw that as the cause. On mine (i had the same/simular problem) I stumbled upon the solution as either the plug or the computer. I swapped out the wiring harness (least expensive option) but that did not fix it so i replaced the computer. The computer usually goes due to the solder cracking and simpy resoldering fixes them. Mine however failed somewhere on the inside and could not be easilly fixed so i had to replace it.

As a result of my troublshooting i have a known good spare wiring harness if anyone needs one that i can let go for cheap.

 

yeah mines located on firewall. Try wiggling the computer connectors while the car is idling and if it dies then that is your problem. Sometimes ziptieing them tight can fix the issue but for me it didnt and required me to cut and splice a new connector on. I also have the connectors tightened to computer with two bars of flat steel with bolts on the ends kind of like a big ziptie. Im not experiencing any more issues.

 

Thank you Kyle, I'll check out that connector for wiggles and giggles.
Appreciate the feedback!

 

Is your 96 ZJ OBD1 or OBD2? Is your fuel gauge working ok?

 

yes. and obd2

 

Ok new problem. Jeep was running good since I swapped the computer connector but then last few dies it started dieing again. Today I put seafoam in the motor and It died before I got to the point of it billowing smoke out of my exhast. Ironically now I am getting now voltage to the coil. Tmrw I am going to test some electricals, Any ideas. Motor isnt hydrolocked but I have no spark now and no voltage to coil connector or coil.

 

With the help of my mechanical team (Nyala and Clark), whom love to ride in the back, we found a rotted wire from the alternator.
This Red wire, approx #6 or 8ga multi strand was rubbing on the battery tray for the last 23 years, rubbed about half way thru.
The wire had lots of green, more than me the morning after the night before.
We cleaned it up as best as possible, stuck a soldering iron in there and fed in some solder, taped up to finish.
Didn't seem to be the total resolve. We intend to cut back clean and connect/splice this week end with some hardware I've cobbled together.
Will let you know the results of that. Check that area on your ZJ for possible similar wear thru. Lucky the battery tray is plastic.
Also had a crank no start at end of last week, -17C morning.
It started fine last week end when the weather warmed, checked fuel pressure, 1st key turn 10psi, 2nd key turn 20 psi, 3rd key turn 30 psi
Started and ran at 30 psi +/-1, consistently. For the 95 -96 year, should be 40 +/-1 psi. So it is running but at less than ideal pressure. The pressure regulation is in the fuel pump assy for those ZJ's. After running lost 3 psi in 15 min so check valve seems adequate.
Fuel pumps here start around $300 cdn. The gauge was a Snap On, but I am going to get a second gauge and retest prior to putting out those $
Will also put in a fresh fuel filter.
My mechanical team will let you know the results.

 

Is the 95-96 different than the 97? Because for that the pressure should be 49. The regulator, not the check valve, is what maintains pressure with key off. Sounds like its holding ok there.
The red wire to the alternator is a fuseable link. So not just any wire will do, unless you want to live on the edge. Its the circuit breaker between alt and batt, will save a car fire. Is there a fuel filter other than the two in the pump? Not on a 97.
Blasting with seafoam is ok but it will take out your TPS. Are you throwing any codes?

 

Wanted to do a recap. I'm sure this post will curse the ZJinx and it's probably out there in the driveway catching fire in a rainstorm.
However, replacement of the fuel pump has finally (somewhat) resolved the hard starts and rough running issues.
Wasn't an easy fix. Did have the tank run close to empty prior to dropping it. Nice light weight plastic tank. And since it had a new pump in a few years ago (Spectra Premium $260 Cdn), the stainless straps I had made were in good shape and the fuel inlet I had fabricated was easy to disconnect from the rubber fill tubes. The strap bolts however were a major pita. About 4" each of unthreading, tight the whole way? WTFish? Corrosion.
Put a brass wire wheel on drill and went up and down the stems to remove the rust from the threads, lubricated, and the ratched box end wrenched most of the way. About 2 hours later I hadn't broken the stems. Cleaned up again thoroughly once out. Reinstalled again with thread protector sleeves zip tied over the exposed threads and lubricated the threads with ultra copper anti seize under the sleeves. Perhaps will need to come out again in the future.
So went with the Spectra pump (again, APC and Napa listed Denso and Bosch at +$110 the price, but could only get the Spectra Premium brand (perhaps it's a sphincter premium pump?) $270 Cdn.
The new pump wire harness was a little different, had a connector at top of pump and about 14" of lead to another connector that would mate with the trucks power harness. Harness had that new "made in Chin" look about it. Yes the Spectra pump is made in China, land of zero defects (they ship all production, let the customers sort their quality). However the other brands weren't available and I needed the truck up and running.
Good cleanup and repaint above the tank, then all reinstall. Click connector in, all good!
Then major hour long fight with the rear connector on the fuel filter, would not unclip, didn't break it, just took a long list of cursing before it simply popped off. The front connector on the filter came off in about 10 seconds. Finally new filter on, add some gas. Prime the line, 41PSI at the fuel rail, starts right up. (Old pump was still running but at 29-30 psi). Rough running, poor starts, poor power in passing kickdown.
So she starts and runs well with the new pump. Kick down the throttle for passing, all full of rage and vinegar, and pulls like a mule. Good starts, smooth running.
For about a week. Then a long series of no starts. Many key activations to get the pump to fire. With gauge connected, 0 psi at key actuations. Then intermittently there is pressure. WTFish?
Then died (luckily just pulling into the driveway), coasted to parking spot.
Time to punish the ZJinx. Made is sit for a time out in the corner of the driveway for two weeks. A pita having this vehicle down and my daughters demanding wheels.
Then one cold day, went out, it had repented and started 1st try. Quickly pulled it into the garage and onto the ramps.
Relays in the master of the universe fuse electrical control centre (black box under the hood) tested ok for working? But I was suspicious so I replaced the Master Death Switch (Auto Shut Down) and the Fuel Pump Relays with new from Napa.
The fuel pump was activating 8 out of 10 tries. Pressure still at 40 +/-1 PSI.
The tank was of course, full at about 160 lb of fuel, didn't want to try and drop it. Undid the accessible connector, sprayed out with contact cleaner and dry air, lubed with dielectric grease and reassembled.
So far 100% starts, hot, cold, wet, dry, and pressure still up there at 40.
So the method is flawwed in that I can't pinpoint the full fix, relays or pump connector? Or just Jeep black magic lulling me into a sense of contentment?
Bottom Line: The overall fix to the bad running was fuel pressure delivery. No matter how you get there if your having problems like Kylesjeep24 and the Peep HelloKitty from Hell ZJinx; a fuel pressure test may reveal the area to correct.
Best of luck to all.