I ran into the exact same issue as far as stalling, losing power, etc.... I mean the exact same. Turns out the fuel pump was on its last legs.

 

Need to do a fuel pressure test, if that checks good...I'd learn toward the cps.

 

i would start by wiggling wires on pcm.

see link below for more info

 

Absolutely. Fixed mine. Do this while it's running. If it starts to stall, remove connection, clean pins with exacto knife, reassemble with dielectric grease.

 

My 96 ZJ did the same thing before I bought it. I would go from throttle to idle and it would stall. I took a chance and bought it. A tech at work asked if the battery was dead. It was, He told me to swap for a good battery and drive it for a mile or 2. The IAC motor needs 12 volts and if the battery is dead it will not relearn. I swap the battery and stalling was gone. I hope this may help ya.

 

I've replaced the battery (used a known good one from my 96), new ignition coil, new cps. Checked fuel pressure, getting about 45-48psi while cranking. I hate just slinging parts so I've really gotta narrow this down.

I've also noticed that the warmer it is outside, the higher chance it will have issues. When it's been aboit 40 in the morning it starts just fine, then it's about 55 mid to late day it just cranks or only starts after a struggle.

 

Subscribed my 98 5.2 lt just started this very same thing last week took out the iac n cleaned it real well no avail wires on PCM look tight idk

 

Check the Dirty Dozen.

 

Yea, I'd been doubting the PCM too, as I pushed / wiggled it multiple times all doing nothing. Turns out I was messing with the wrong plug. Of the 3 plugs, I had been messing with the last one (close to engine). It's been sitting for 3 days at my job and unable to start at all. Pushed the plug into the PCM closest to the fender and wiggled it around, was able to get it to start after a struggle and stayed on. With it running I wiggled the same plug and got it to stutter and then shut off.

Tomorrow I'm going to take all the plugs out, clean them with electric cleaner, and put some dielectric grease on the connectors, and zip tie them all snugly. I'm thinking that'll do the trick.

 

take the tps out too and clean it mine would stall at lights and randomly try to surge forward it was the tps I just replaced it as it was cheap but you should be able to clean them just a thought

 

My solution(s) for stalling.

PO: I know this problem plagues many ZJ owners. NO Jeep continues to have more problems than mine ! Previous owner(s) fault more than Jeep.

I fought this stalling issue for nearly a year after purchasing my ZJ. All the items suggested by fellow posters are points to evaluate, check, clean up, tighten, etc. As for me I dutifully handled each suggested solution. It is just part of buying any older vehicle.

Yes, eval the PCM, secure and tighten. Seemed to help...for awhile. Clean the IAC, that helped too. Replaced the TPS, eliminated that possibility. That too worked for a few weeks. I replaced the MAP sensor and the vehicle vastly had improved performance. A few weeks later, the headache returned, although less often. Hmmm.

So I asked myself, all the solutions made a difference in performance, then the stall returned to cause me headache later, why? In all cases I had been jiggling and working with the engine electrical harness at various points. Time to take a few hours and inspect grounds, connections, stress/strain points.

Oh man, some corroded chassis grounds. loose and failing engine ground (under the alternator on the 5.2L). Repaired those. Found the coil to be simply worn out from being toasted since new. It was low cost, so R&R it. Wiring harness had many points of chafing and wearing outer wrap and insulation. Secured those to eliminate contact with sharp areas of chaff zones.Look underneath as well. I found harness to forward O2 sensor contacting exhaust..oh that was nasty looking.

If you haven't, replace the plugs and wires. My owners books says every 30K for the 5.2l, they looked ancient. Just do it. You are already under the hood and slimed.

On inspecting the three wire sub-branch harness to the MAP sensor, I found the sensor wire had been crushed into the ground wire along with minimal insulation left on the +5VDC wire. How in Hades had that ever been done?

Gently separated the three wire harness, cut out the damaged section, used shrink tubing and like wire, replaced and soldered in new lengths of cable. Positioned and heated the shrink tubing over joints. Wrapped with spiral wrap to protect from heat and crush damage. Started engine...Puurrrr.

Since that day with hours spent inspecting and repairing electrical system. NO STALLING HAS OCCURRED this past year !

CONCLUSION: Did I feel bad about replacing a few sensors that did not totally solve the initial problem, well, kinda. But in each case the performance of the vehicle DID improve. Who knows when the last time any of these components were last replaced on a 160,000 mile vehicle.
Do take the time inspect your wiring harnesses.

BTW: With the exception of the harness repair I did for the MAP sensor, all that I have written is available on this great forum!!!

I still have the ZJ and it is STILL testing my patience. As of this week, headliner fell, backup lights only work when I press shifter to dash, grinding/moaning of vehicle when making left/rht 90 degree turns into parking spots.

Ahhhhh, we all need a good puzzle/hobby/tormentor/fun car to justify a dedicated beer frig.:cheers2: :cheers2:

Oh, nearly forgot. My 5.2L scoots along at 60 to 65 mph drinking 18.7mpg. About 14mpg around town. That is on street tires Firestone LE. Later

 

Wiring harness had many points of chafing and wearing outer wrap and insulation. Secured those to eliminate contact with sharp areas of chaff zones.Look underneath as well. I found harness to forward O2 sensor contacting exhaust..oh that was nasty looking.

On inspecting the three wire sub-branch harness to the MAP sensor, I found the sensor wire had been crushed into the ground wire along with minimal insulation left on the +5VDC wire.

Great input, these are exactly the kind of things I had in mind when I wrote the wiring section of the dirty dozen. It just takes time to do it. One fellow found his main harness eaten by vermin where it passes through the firewall. You cant make this stuff up.

Those sensor manufacturers are getting rich off this type problem. I have a box in my shop with about a half dozen sensors with 100k on them. Probably nothing wrong with them.

 

Yea, ZeeJay 1997 it is mind blowing. And a big THANKS to yo for your tips two years ago while I was going bonkers with the PCM !

HA!, yep, I too have a box of Jeep GC parts that I suspect some are fine but exasperation & desperation moves in sometimes so parts just get replaced in a "while I am in there" mode of thinking.

Today is another problem. Weird clicking and ratcheting sound of doors moving in the heater/AC box. It definitely is not normal. Too much is failing now at 166,000. The Jeep was badly maintained by two owners before me. I thought I could give it new life, but I am having second thoughts.

A salute to you again for the PCM help ! R&R the PCM, cleaned the connectors, large nylon ties to secure the three connectors, and no more headaches. Whoever designed the computer to be in the WORST environment was not thinking well that day. In the cabin on the firewall would have been an easier life.

 

You can replace every mechanical component in a ZJ with new or Mopar remanufactured components for around $20,000 according to my numbers the last time I priced everything out. This also includes sensors and the powertrain harness. I believe I also figured reupholstering the seats and headliner, and replacing the headlights in that number.

Maybe go and buy everything all at once. Still cheaper than a new Grand. :laugh:

 

I cleaned my IAC for low idle with no change. Really bad with A/C on. Was about to order new part but saw adjustment instructions from Airtex on Rock auto site.

Part should extend no more than 28mm or 1 1/8 inches. Made the adjustment to this spec and runs like new with 170K!
:cheers2:

Follow instructions on this link: ww.airtexve.com/custom_searches/showdiagram.php?file=instruction_sheets/990700385.pdf

 

Just to update, the thorough cleaning of my PCM did wonders... for a few days. Used electric cleaner on the pins and harnesses, used canned air on em, then put a dose of dielectric grease on the connectors, fastened it all in tight with zip ties. After a day or two, I would get a random stumble, like the whole issue starting from the beginning, then yesterday it backfired and shut down in traffic. Wouldn't restart until I got under the hood and pressed firmly on the leftmost wire harness going into the pcm, then it fired right up.

I got to wondering why I never had the same electrical issues on my 96 ZJ that had almost 200k. I looked under the hood and even though the outside of the pcm was very dirty, there was a piece of molded black plastic covering all three connectors, as an extra shield from the elements. I don't know whether the PCM can be switched with my old one, I know that's a whole other issue in itself.

 

On the failing vehicle, #s on the PCM are P/N P56044406AC followed by 56044 in small letters and 406AC in big letters.

On the older vehicle that never had electrical issues, the #s on the PCM are P/N P56043172 followed by 56043 in small letters and 172 in big letters.

Any idea if I can swap the old into the new?

I was about to do it anyway and then thought, "What's the worst that can happen"? So really... what IS the worst that can happen?

 

there are standard emission pcms and California emissions pcms. if the vehicles are the same type emissions and both have 4.0 engines, they are interchangeable from 96 to 97.

nothing bad will happen if you try it.

 

I've swapped the PCMs, and it does start up and idle, but I get a hard code of P1765 "Transmission Power Relay Circuit". No codes prior to unplugging the old computer. I haven't tried to drive it since the swap.

Did I just blow a relay, or is this an indicator the PCMs are not compatible....?

Edit: I cleared the code, swapped the Trans relay with the horn relay, got everything put back together, and it started up and drove just fine, no more codes. Lets give it a few days and see what happens!