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General discussion

Jeep Grand Cherokee stalling fixed!

May 18, 2007 12:44PM PDT

Found that the outboard PCM cover screw was shorting out the circuit board. Chrysler PCM p/n P56028412, s/n TEH106636023.

Short story long: I have a 96 Grand Cherokee 4.0L, 125,000 miles. Several weeks ago, I started to have stalling issues. Hot or cold, dry or wet, first drive of the day or last, it didn?t matter. The engine would cut out. It felt like it lost all electricals.
At the time it was showing an ASD relay code. Swapped the ASD and A/C relays. Same problem. I didn?t have time to look at it, so I had the dealer go through it. After 2 days and $200, they called and said it was the ASD relay, and that they put in a new one, and it?s all good. Um, ok, maybe I missed something. I?m a trusting soul, but let?s see if this fixes it. The next day the problem was back. I went back to the dealer and they basically said, ?We don?t know what it could be, good luck with that?. Now my wife knows why I don?t go to the dealer. By the way, the old relay tested good.
My turn. Being the methodical aircraft mechanic that I am, I grabbed a multi-meter, contact cleaner, and wiring diagrams. I cleaned connectors, ohmed out wires and sensors, checked for power and grounds. Everything checked good. By now, it?s showing ASD, crank sensor, and primary ignition codes. Then, with my wife trying to start it, I wiggled the connectors on the PCM. Every time I wiggled the gray C3 connector just right it would run. When I let go, it would die. So I took the connectors apart and tightened up the crimps (I don?t recommend doing this without the proper extractors and crimper). Threw it back together and BAM! Same problem. Well, time to bite the bullet and check for bad solder joints on the PCM board. I took the cover off of the PCM and realized that looking through the potting compound is like looking through Guinness Stout. But, I put it back in and hooked it up. It started stronger than ever, and didn?t even think about stalling. Yes! I figured that I finally got the connectors sorted out, so I left it over night to cool down. Got up the next morning and it started right up and wouldn?t stall even when wiggling the connectors. So I put the cover back on, put the PCM back in, hooked up the connectors, and BAM! It wouldn?t start! That was the point when my wife asked, ?How?s it going?? And I, being the methodical aircraft mechanic that I am, said, ?what the ----?? That?s when my wife turned around and went back into the house. While smoking a pack of cigarettes, I thought, ?Gee, it runs with the cover off, but not with it on.? DUH, wonder what it could be? So I backed out the two screws that hold the cover on and BAM! It started right up. Then, while it was running, I tightened the outboard screw and sure enough, it died. Yes! Aircraft mechanics love it when they can make things stop working. I installed new screws (1/4? long, factory screws are 1/2? long Torx head), and she?s been running great ever since.
Now, will this fix a bad crank sensor or idle air motor? No. But it is an easy trick to try before going to the dealer and having them throw expensive parts at your Jeep and seeing if any of them stick. Just back out the cover screws about 1/8?-1/4? (don?t worry, nothing will fall apart inside). If it fixes it, great! Spread the word. If not, use logical trouble-shooting steps. Learn the systems ? what will and what won?t cause the problem. Good luck.
As a side note, if you want to see a service manager?s eyes pop out of his head, tell him that you want your money back because your not going to pay them to trouble-shoot a design defect. It?s a glorious sight.

Moderator Note: This thread will popular has grown too unwieldy.
Please make a new post all your own from now on.
Closed as of March 23, 2018.

Post was last edited on March 23, 2018 5:04 PM PDT

Discussion is locked

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Actual Problem
Jun 28, 2008 9:18AM PDT

Based on my, and many others, experiences, the problem will certainly reappear, at some point in time. The 'repair' is most likely related more to removing and reconnecting the 'A' connector, the one on the driver side of the computer and not to the cutting of the screws. The screws go into a piece of plastic which is near to 3/4 inches deep and has little, if any, lateral stress anywhere. If you want to try to make the computer fail, push in (toward the firewall)hard on the top driver's side of the ECM. It will almost certainly stall. Nothing special, hot or cold, day or night -- just press hard with your thumb. If the car doesn't stall (very unlikely), then you are not one of the unfortunate ones. On the other side of the coin, if you force the driver's top of the ECM toward the front of the vehicle with something (like a 3/4 inch hot water PVC pipe elbow) you will likely be unable to make the failure occur , no mater what you do. Fixed? Of course not! It just tells you that the computer is indeed defective. Please see my post at # 117, and others, because replacing the computer is not only expensive, it's not always that simple. The replacement needs to be a properly programmed to your VIN# unit that is suitable for your vehicles wiring. Mine was a 406AB and nothing higher than a 406AC would accept the proper programming, causing the truck to start, but not RUN. Unless you know if your vehicle has had any ECM 'updates' installed, it is probably safest to get only the base programming done.

The worst thing about the majority of these failures is that THEY SHOW NO FAILURE CODE. The reason for this is almost certainly that the BATTERY VOLTAGE (going in at the 'A' connector) is being lost and the computer doesn't see any error, it just goes to sleep and then starts working again when and if the problem (loss of voltage)goes away.

Regards,
Jim

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Actual problem
Jun 30, 2008 3:31AM PDT

You ar right. after cutting the screws, my problem came back in a few weeks. I will try pushing in on the driver side of te PCM to see if it fails. Where is the best place to get the pre-programmed PCM?
Has anyone bought a PCM pre-programmed based on the vehicle VIN number and it works? I know Solo Auto Electronic (1-800-886-9926 Mopar specialist) does that for $290.00.

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My Source for JGK ECM
Jun 30, 2008 4:23AM PDT

Allcomputerresources.com 1-866-699-5230 has these units for $245 includes shipping from Florida. The first unit shipped did not work on my truck, but they quickly sent another that did work. Talk to Ryan. Or you can buy from Mopar for over $600 and likely have the same problem at some future time. This failure is widely know about by the rebuilders. It's just a matter of finding out which core will work on your truck in order to get back up and running.
Regards, Jim

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Ok another stalling here!
Jul 5, 2008 7:56PM PDT

Well my ZJ is a "98 5.2 after reading all this thread. My prome is kinda similar, but on mine the jeep it starts run 2 or 3 seconds then, shut off. I have spark and fuel. When i plug my ELMSCAN OBD Scanner, after trying to detect the OBD Protocol it says Connection Error. (this started when the jeep came with this problem) So I have some doubt's

If i check continuity from PCM Case with the Negative Battery pole. there isn't, but if i check the PCM Case with the Positive there is !! Is this right?

So this might be that i need a new PCM ?

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NEW STALLING
Jul 5, 2008 10:40PM PDT

u ARE IN THE CLEAR AT THIS POINT. THE GROUND SHOULD NOT CONNECT TO CASE. CASE IS A COMMON(+) POSITVE TO BRAIN. THE PRESSURE TESTS;ISTED IN PRIOR POSTS IS THE MOST INDICATIVE OF BAD BRAIN. "ASD" RELAY AMOUNGST OTHER RELAYS FAILURE OR BAD CONNECTION IS GOOD PLACE TO LOOK. hAD THIS PROB FOR 18 MOS / THREE BAD BRAINS. TURNS OUT THAT ORIGINAL BRAIN DROPPED INFO LINK TO VEHICLE ID. THUS IT DIDN'T KNOW HOW TO ACT==NIETHER DID I. THANKS TO A SHARP REBUILDER THAT IS WATCHING FOR THESE HANG UPS i GOT A GOOD BRAIN AND HAD IT PROGRAMMED AND UPDEATED PROPERLY AT A FIVE STAR DEALER...MAKES A DIFFERENCE... AND GOT IT DONE AT NO CHARGE. RESEARCHED THIS THOROUGHLY. THERE ARE OTHER INDICATORS GOING ON AND U NEED TO NOTE THEM AND TRACK THEM. LOTS OF "IF'S". BECAREFUL U COULD SPEND ALOT OF MONEY AND NOT GET A FIX.
-----READ ALL POSTS---SEVERAL TIMES ---GET AFEEL OF WHAT THEY ARE SAYING AND TRY THEN READ SOME MORE AND TRY AGAIN----- NOT ALL PROBS LEAD BACK TO BRAIN FAILURE. THIS A TRICKY PROBLEM.

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new PCM
Jul 23, 2008 6:55AM PDT

Well, I've tried all the simple fixes (cut the screws, wrap the mounting bolts in electric tape & install plastic washer etc.) because i'm always for solving a problem with a few bucks first rather than spend big bucks to find out the problem still exists. I've come to the consensus that while the car will not stall for a few days after unplugging the connector cables to get to the computer, the problem always returns.

I'm beginning to agree with you based on all of the trial and error that the problem is due to the disconnecting and reconnecting the the cables to the computer, however i've not been able to get the car to stall by pressing on the upper right side of the computer with my thumb. I've been pushing hard, but maybe not hard enough. How can I be sure that the problem is the computer and not the connector cables? Can I be sure? I'm about ready to just buy the computer already because the constant stalling is ridiculous.

will allcomputerresources.com work with me to ensure that I get a PCM properly flashed with the correct updates?

Thanks for your help

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piece of crap 1996 jeep cherokee larado
Aug 28, 2008 10:09PM PDT

I have just purchased a 1996 jeep cherokee larado. It starts ok, but will cut off while idoling or driving. It does it at different times and does different things. Sometime it shuts off with no warning and sometimes it misses and then shuts off. I have noticed that the rpm guage flucuates all the time and if it drops below 1000 rpm's it will shut off. It has a 4.0 inline 6 cyl motor. The only code it will read is ign/coil, so my mechanic has replaced the coil. That only made it worse as now it is backfiring and cutting off too. We have replaced the fuel filter and upon reading this post we unscrewed the screws in the pcm half way and nothing is helping. I am an out of work mom of two and i am scared to put my kids back in this car. We need any suggestions. thanks

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Sell the car???
Aug 29, 2008 2:32AM PDT

Sorry to hear it.

Just purchased jeep... Can you find the old owner and get list of parts replaced before you bought it. This will help when trying to determine what parts to replace as you go down the check list.

If bought from a car lot... you have, I think, 3,000 mile Automatic warranty, but dealers don't tell you that, but it is the law... call state attorney office to verify... used auto warranty. Next... try complaining to the dealer and maybe trade in car for another one or maybe sell the car... Helps car run better after driving 50 miles.

If you have to keep the car
First... Read all posts and take notes or copy and print posts the resemble your issues... will take some time, but after a while ,you will see a pattern...

One good post to read is...
Post #237 of 256
What I did before I bought the computer
by gconcepcion - 8/13/08 12:49 PM
In reply to: Fixed... ??? by Cat5 Cane

keep in mind that post numbers change when someone adds new post to the board like I'm going to do when I add this post. So read the topic heading


Also... try adding a gas additive to the gas... Gumout or Lucas gas treatment... it cleans the Fuel Injectors that cause similar problems to yours... costs approx $5.OO from auto parts store NAPA parts store, Auto Zone, Discount Auto Parts, PEP auto Parts... ETC.

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sorry correction
Aug 29, 2008 2:37AM PDT

somehow words got misplaced

Also... try adding a gas additive to the gas... Gumout or Lucas gas treatment... it cleans the Fuel Injectors that cause similar problems to yours... costs approx $5.OO from auto parts store NAPA parts store, Auto Zone, Discount Auto Parts, PEP auto Parts... ETC
...............Helps car run better after driving 50 miles.

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Stalling -check you Battery for low water
Mar 10, 2010 12:12PM PST

96 Jeep Cherokee Ltd. has been stalling for a couple of months. Seldom at first, until it stopped only when on stop signs, bumps or afer a long drive. Cleaned Thottle bottle, then replaced it, RPM gadget, sensor (don't know which), cleaned the battery/cables really good and finally Fuel pump. driving off after fuel pump changed out, stalls again, and once more before arriving home. I stayed up until 3:00 am reading all these entries and finally someone said he changed out the battery. In the morning started good, opened hood, moved cable stopped! got flashlight and butter knife, took top off battery and saw very low on water, filled up both sides with 4-cups of water. started the Jeep and has been running like a dream. If nothing else check you battery for low water or may need replacing. Then try one of the other things. My next move was replacing those long screws from the PCM. Good Luck

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Dont Buy A New PCM!!!
Jul 6, 2008 11:26AM PDT

I have the permanent fix for the JGC stalling problem. Most likely your PCM is fine. The problem results from the PCM grounding on the PCM casing. There are four bolts that mounts the PCM to the firewall. There is a metal to metal contact between the PCM casing and the four mounting bolts. This results in the PCM becoming grounded and causes the vehicle to stall. ELIMINATE the metal to metal contact and the vehicle will not stall anymore. I did this buy installing plastic washers and wrapping the threading of the bolts in electrical tape, and the problem has not returned in over 5000 miles.

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thanks for the advice
Jul 20, 2008 5:32PM PDT

Thanks for the advice, the problem did indeed return after about 3 weeks. I've followed your directions for covering the mounting bolts in electrical tape and installing washers to eliminate all metal-metal contact. The only difference is that i've found there are only 3 mounting bolts, not 4 like you mentioned. Is there another one that i'm missing? By removing the 3 bolts I was able to completely remove the PCM so I don't think there could be one that I overlooked. My PCM Part # is P56028412

At any rate, i'll drive it around for a little while and see how it goes. If this doesn't solve the problem, the only option I have left is to buy a new PCM... But if I can solve the problem completely for ~300 for a rebuilt PCM, i'm all for it.

Thanks

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RE: PCM Casing Bolts
Jul 21, 2008 4:21PM PDT

Not sure why you are missing the extra bolt. My problem was the top right bolt. Try pushing the pcm inward while the engine is running. Does it stall? Keep me posted.

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stalling fixed!
Aug 12, 2008 5:11PM PDT

The problem continued to get worse until it was stalling anywhere between 2-10 times a day. In addition, I would sometimes lose power to the fuel injector so I would be driving and unable to accelerate, although it wouldn't necessarily stall. I decided that the problem had to be either the computer or the connectors, so I broke down and ordered a remanufactured computer from autocomputerexchange.com.

I live in Hawaii and it took more than 2 weeks to get the computer even though I paid for the UPS 2-day shipping. They wound up shipping via USPS Priority because I was told "Hawaii is not one of the 50 states and we only ship UPS to the 50 states." I understand that shipping to Hawaii is cheaper via USPS, so I have no problem with that, but telling me that it's not one of the 50 states! HAH!

Anyway, I eventually got the computer, put it in, and my problems appear to have been solved. I'll keep you updated if the problem re-occurs, if you don't hear anything from me, assume everything is good to go!

I would recommend buying a computer from autocomputerexchange.com if you decide a new computer is what you need.

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Fixed... ???
Aug 12, 2008 8:16PM PDT

gconcepcion ...
Congrats... to U and I hope this is the final fix too...
Who did you order from (guys Name and #)and did you get the extended warranty? how much did it cost for part and labor? Can U list (in order) all parts replaced before the PCM... but it could help someone else out to use as a checklist...

lastly.... to top it off... If car was backfiring, suggest to use injector cleaner (like Gumout or Lucas) in gas to clean fuel injectors...

Cat

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What I did before I bought the computer
Aug 13, 2008 5:49AM PDT

It was only happening once every few days at first so I replaced each of these one at a time waiting until it would stall again until moving to the next part:

Oxygen sensor (I had changed this a few months prior so I ruled it out as the problem component)
Idle Air Control Valve
Throttle position sensor
Checked fuses and relays

At this point it had been happening for a few weeks, happening more frequently as the weeks progressed so I brought it to my mechanic to take a look at it. He checked the crank position sensor, fuel injectors, spark plugs and distributor and could find nothing wrong. He didn't charge me because he couldn't figure out what was wrong and couldn't reliably reproduce the problem to troubleshoot it effectively. He thought it was possible that it might be the computer, but didn't want me to spend the money if he wasn't certain that was the problem so he advised me to drive it until it completely died and then he would be able to tell me exactly what the problem was.

I took it home and drove it around for a few weeks, and it would stall everyday that I drove it. I tried cutting the two screws that started this thread and the problem went away for a week or so, but quickly came back and got worse. I then tried insulating the mounting screws that "jetmech" mentioned in this thread and it seemed to work for a day or so. I now attribute the temporary no stalling due to my unplugging and replugging the connectors into the computer, perhaps making the connection temporarily better, but the problem would eventually return.

Over the weeks the car would sometimes take a while to get the engine to turn over (10-15 minutes) but it would always start eventually and I would be able to drive 20-30 miles no problems, although it would still occasionally stall. About two weeks ago I finally got fed up with it and I couldn't even get it started anymore. At this point I decided to just pay the money and order a remanufactured computer.

I called up allcomputerresources.com (as mentioned by Jim Mccain) and ordered a computer from "Ryan" 1-866-699-5230. (I typed autocomputerexchange.com in my previous post, but I got mixed up. I looked at their site, but I actually ordered from allcomputerresources.com)

The part cost me $245 + $25 UPS 2nd day shipping. You get a lifetime warranty on the computer that begins when you send them back your old faulty computer.
I did all of the labor myself from the beginning of the problem to end (with the exception of my mechanic looking over the vehicle for no charge) so I saved alot of money on labor.

I'm not even close to what you would call a mechanic so this is definitely something that most people would be able to do yourself with the help of a good manual (haynes or chilton) & the resources on these forums.

The entire process including parts (Throttle position sensor, Idle Air Control Valve + Remanufactured ECM) cost me <$350

Hope this helps somebody!

*All parts except the ECM were purchased from my local NAPA auto parts store

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BTW
Aug 13, 2008 5:52AM PDT

Forgot to mention per your asking. My JGC never had a problem with backfiring. I've seen several people mention that they had a backfiring problem, but it never happened to my 1996 JGC. Maybe it would have if the problem had gotten worse, but I never experienced it.

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gconcepcion great read for everyone else
Aug 14, 2008 1:27AM PDT

To gconcepcion
Thank you for the added info to help others...

To the other guys... Guys, remember when you came here and asking for help... it's all about us, helping each other, cause the dealers don't care, nor do they know the answer....

Remember to come back after your fix to tell us your steps and what was the final fix at the end in a final format

One for all...

Cat5 Cane

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update, stalling still fixed, but having other minor problem
Aug 24, 2008 1:30PM PDT

Just an update, it's been almost 2 weeks since I installed the remanufactured computer and everything is still running strong! Not even a hint at stalling!

However, i'm having weird problems with my gas gauge reading "Empty" when I first turn the car on despite having a full tank. If I turn the car off, and turn it back on, it will go back to normal and accurately tell me how much gas is left. Is there a fuel gauge sensor somewhere that needs to be replaced? Any ideas?

and the passenger side air conditioning leak into the floormats has returned after my 2 year old DIY fix stopped working. It's now leaking out of another as-of-yet unidentified area so I'll have to do some hunting around under the carpets...

One thing that i've learned about owning a jeep is that once you finally think you have a problem solved, it's only a matter of time(usually short) before something else goes wrong.

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Jeep GC stalling fixed
Jul 7, 2008 6:05AM PDT

This is for the Aircraft mechanic who came up with the solution for this common problem......THANK YOU!! I tried your method and I'm here to say that so far,so good. I have driven my Jeep for some time now and the stalling problem has not returned, anybody else out there with this same dilemma should try this technique, just 2 screws, 1/4", my only regrets are that I did not find this out earlier( Approx $3,000 in repair cost's at the dealer) and I can't buy this guy a cold one and shake his hand to show my appreciation.

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Here I go go again!
Jul 16, 2008 12:33AM PDT

Christmas day I found this forum, did the screws trick and viola! Jeep instantly ran wonderfully.
Come June, stalling, back-firing, and shut down returned.
Blew out another catalytic converter after being replaced Nov. prior.
Messed with screws a tad--seemed to help, though random stalling still occurred.
Had my mechanic install a straight pipe as I didn't want to blow out another cat conv.
Day or two later, big back-fire and stall. Had to make road trip and Jeep seems to make one-two stalls once on open road then drives fine.
Stall seems like too much gas is being pushed. Engine cuts and rumbles and rpm is lost. Once parked I can smell gas and engine acts like it's flooded. Once I wait 20-30 seconds Jeep starts up and moves along.
Took Jeep to mechanic due to rattling (assumed he didn't install pipe well). He finds muffler is blown from back-fire, doesn't want to work on my Jeep anymore!
So, I have a computer coming. I'm going to make other checks and apparently it's all on my own since I no longer have the mechanic!
Waiting to get new muffler installed until it seems back-firing is eliminated.

Any thoughts?

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To Here I go again
Jul 16, 2008 6:27AM PDT

w/o knowing iffn any codes were set, speculation is that the crank angle sensor or cam angle sensor may be intermittently failing. Had these probs and brain problem for 2 years myself. iffn no codes were set then it is probably bad brain but not neccesarily so... could be intermitten power loss at ASD relay--clean all relays with tuner cleaner(got some at Radio Shack with an oil init that prevents corrosion and seems to last well over a year wtihout reapplication..However the gas smell says that fuel pump isn't failing so it has to be ignition loss so I would look to sensors and brain. Sensors will set codes the brain will not.
You can check the cam and crank anle sensors with an ohm meter. b est to have a digital but if u disconnect them from the wiring harness u can use an analog. IF u happen to replace the brain make sure to get the right one for ur vehicle using the code off of ur present one, cross referenced to VIN. Then get Vin and mileage programmed into it by someone who is familiar with chrysler and Jeep electronics. I went to a five star dealer and got mine done and updates installed. Talked to Mech there and found that the updates are recalls and makes the reprogramming free.... also before jumping to changeing things test first. Look behind the brain and make sure that the case of the brain isn't grounding out on bolts coming from A/C unit mounting to firewall and the nylon grommets are in place for the mounting bolts.

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1997 Jeep Grand Cherokee Laredo wont start/stalling
Jul 23, 2008 1:58AM PDT

I NEED HELP!! i HAVE A 97 grand cherokee thats been giving me problems. In the past month i put 3000.00 into it and im getting sick of it. Usually in the morning or when i have not driven it, it won't start until 5 or more tries. Then it will occasionally stall when I am coming to a stop. Please someone help! i live in Pa and i am going to school in AL and i need to drive this jeep there at the end of August and i need a good working SUV. Thanks

Parts replaced

Exhaust Manifold
Spark Plugs
Distributor
Crank Sensor
Idle Control Motor
Brakes
Rotors

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beno590 won't start
Jul 23, 2008 4:48AM PDT

First things first: A: did u read the previous posts? B: Are there any codes present in the brain? C: What tests have u performed; or are u just repalacing parts hoping to fix something?
If u read the forum then u know to enter all the info u got to get the most help we can give. Sooooooo in the dark here but need to know iffn there is 12 volts getting to the coil when u crank it in the morning. a cheap plug and play fix without testing anything off the top of my noodle basket wud be the ASD relay or connection thereof.. tuner cleaner will clean the connection.
NEED SOME REAL INFO.....mileage,codes present or not. can u hear the fuel pump run....last time the filters were changed; have unplugged and replugged the brain; When u replaced the Idle Control motor did u clean out the orifice in the Intake manifold real g0ood with cleaner and rod ? What kind of fuel pressure and how stable is it? Has the battery gone flat anytime recently... this could cause circuit malfunction in the brain and may need to be updated or flashed.

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Another Stalling Problem
Jul 29, 2008 1:15PM PDT

97 GC 2WD 4.0 S6 Auto 86K miles.

Cranks great. Sitting still at idle, during warm up w/o AC on, stalls (with no stammer) after two minutes. Crank again, stalls (with no stammer) after more two minutes. Just before reaching op temp, hard stammer an dies. Must turn over 8-10 times to crank again. Runs great after initial warm up from dead cold and subsequent starts for the rest of the day.

No check engine codes stored, however the light flashes once only when the hard stammer occurs. No scan tool. (gotta get one of those). Nothing retrieved but 12 and 55 on key cycle.

Done so far:
Fuel Pump - fixed another problem I had before I started.

Cleaned all fuses and relay connections, tightened all socket tabs and put dielectric compound on them. Looks good but didn't fix anything

Swapped the relays around in the PDC.

Checked for voltage drops across all fused PDC circuits.

Ignition coil- the outer case was cracked but replacing it it didn't help.

Checked coolant and air sensor resistance and voltage. 72 degrees=8.3K for both. Haynes says they are both 2K low, but I don't believe it since they read exactly the same. Anyone know what the DC temp /resistance chart says?? Could be onto something.

Removed and cleaned throttle body and everything attached to it to include disassembling IAC and cleaning out the MAP orifice. (it needed it badly) Runs better, when it's running.

Jiggled wires,whacked on,moved around all the critical stuff, ECM, PDC, Junction Block. Gave the two suspect screws on the ECM a good looking and poking. Checked mounting screws to ground - nothing.

I've read every post on this thread and researched a bunch of web sites. Still have some things to check.

From what I gather, the warm up mode is open loop and ECM does not use the O2 sensors unless the sensors are at 600 degrees, but the heaters are on for when it goes to cruise mode. Still gotta check that. Since it runs good hot, it may have problems making the transition if a heater is out.??

The only difference in inputs used between warm up and cruise (closed loop) is the ECM uses O2 for cruise.??

On another note, here is some info I found out there somewhere for those who have never bought a Mopar ECM and think they may need one. This apparently comes with a refurbished ECM. Fine time to tell you this after you've forked out the bucks for an ECM. Some of it is beyond the scope of the home mechanic, but some can help.

Common failures that cause mis-diagnosis of JTEC Controllers:
? Intermittent grounds; Loose or corroded grounds may cause false sensor readings. Verify all sensor grounds terminate at PCM cavity A4 (BK/LB wire).

? Manifold absolute pressure (MAP) sensor and Throttle position sensor (TPS) voltages; check voltage over the entire range, not just the extremes. Whenever possible use an oscilloscope to check MAP sensor and TPS sensor output voltages for noise spikes.

? Verify minimum TPS voltage. Minimum TPS voltage should be approximately 0.5 to 1.5 VDC.

? Idle Air Control (IAC); Shorted windings or intermittent connections. If IAC codes are present, check to ensure motor windings or related connectors are not shorted to ground.

? Heater voltage for upstream and downstream oxygen sensors. Verify battery volts +/-1 volt at all oxygen sensor connectors, DG/OR wire.

? Charging system malfunction; Alternator defective or battery not fully charged. Check alternator output to ensure there is not excessive ripple voltage. Verify battery volts +/-1 volt at PCM cavity A22 (RD/WT wire).

? Sensor voltage supply. Check for approximately 5 volt output from PCM cavity A17 (VT/WT wire) to MAP and TPS sensor, with ignition switch on.

? Distributor voltage supply. Check for approximately 5 VDC output from PCM cavity A17 (VT/WT wire), or to cam/crank connector(s) with ignition switch on and while cranking.

? Auto-shutdown (ASD) relay; Corroded wires or faulty relay.

? Minimum air flow; check for air leaks or airflow obstruction.

? Vacuum system; Contaminants or leaks in vacuum lines.

? Fuel pressure and leak down.

? Vehicle speed sensor operation.

? Crankshaft and Camshaft sensors; Some aftermarket sensors have not worked properly with Mopar engine controllers.

? Splices and Fusible Links; check for open and/or shorted wires.

? Damaged connector terminals; Always ensure holding tabs are securely seated.

? Excessive current on certain connector pins may damage the PCM. Use of a test lamp or a short in the wiring harness of the vehicle can cause this condition. Always use a DVM when checking the unit/system.

? Check Technical Service Bulletins according to model year and system malfunctions

Anyhow, if anyone has any more ideas why this thing is cold natured, please reply. I'm trying to fix it w/o replacing good parts.

Questions: If I get a scan tool, can I retrieve the soft codes that clear when no longer valid. Do these normally show up on key cycle?

May all your Jeep problems be taken away,
Dave

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97 Jeep cold...
Jul 29, 2008 10:42PM PDT

To Dave Da Dodge

Have been here for a while ... reading responses and questions and wanted to take the time to say thanks for your in-put... GREAT POST. Very informative information for the garage machanic... Only wanting to expound on the fact that Jeep electrical parts are critcal. Most aftermarket parts do not use proper wiring or connector to carry the loads that jeeps criticaly demands.... resulting in malfunctions and bad codes.

It's a *****, but it is what it is... Tryng to save money and you replace a part with an After Market part... only to find out 2 months later that the parts not working as designed. Bottom line... Buy Mopar parts.

Dave ... back to you... I'm stretching, but have you checked the spark plugs wires... coil to cap

Good luck... Be sure to come back to tell us your fix

Cat5

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Ignition
Jul 30, 2008 10:20AM PDT

Cat and Diggin,

Thanks for your replies. I thought the PCM info could help someone with the know how. As for myself, I've worked on aircraft electronics for 30 years, so this stuff is not too far from what I do for a living. My problem is that I don't have the equipment I need for expedient troubleshooting. It's drivable now, so I have time to figure it out, or maybe work on it till I'm completely bald and fork out the bucks for a trip to the dealer. I'm stubborn in that respect. Don't like to pay anyone to fix something I think I am capable of fixing myself.

This morning, I jumped in it and drove without a warm up to my park and ride (about three miles) without incident. This afternoon on the way back it stalled once at 50MPH. It sorta feels like an old straight shift when you pop the clutch. Doesnt miss a lick, almost like you cut the ignition off and back on real quick. Yes, I checked the ignition switch under full load every which way it can be checked though the run circuit. (I have a full DC wiring diagram)

I will buy Mopar, but I want to be positive the old stuff is bad before I do so.

All new ignition stuff. First thing I did, as a matter of fact. It needed it.

My Haynes manual gives detailed instruction for checking the sensors. Just Gotta get around to it.

The brain dump thing makes sense. I left my ignition switch on until it killed the battery several months ago, but I can't make that connection to the problems starting.

I'll try to send y'all a sheet with the detailed operating modes of the ECM. It's too much to post here. About five pages. Googled it up the other night, but can't find the source now.

I'll keep you posted
Thanks again
Dave

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Cutting out /missing...
Jul 30, 2008 7:34PM PDT

My car skips every now and again too.
A couple of days ago the car's red light came on again... check engine today. Scanner say 300,302,305... cylinders 2 and 5 missing.

Possibles...
spark plugs,
cords,
ignition,
coil,
injectors,... Ahhhh, Hummmm, maybe dirty and clogged, so I added gum out to the gas and we will see!


Lets hope!

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If I only had a brain
Aug 18, 2008 4:46AM PDT

A dodge tech on another board suggested tapping on the ECM with a rubber mallet. BINGO!

Lightly and rapidly tap the side of PCM / ECM with a rubber mallet, engine dies. Never fails.

More to follow...

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Relays
Sep 2, 2008 10:16AM PDT

A suggestion to anyone having intermittent problems. Change out all the relays in the power box under the hood. Found 4 of 6 bad / intermittent.

Figured it out by swapping the ones I knew were doing their jobs (horn, wipers, starter) with ones that could cause the problem I was having (fuel pump, transmission, asd).

No problems now that the bad relays are gone.

I'm still on the fence about the PCM.

Dave