'99 WJ will not stay running. High voltage, and other issues - JeepForum.com
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post #1 of 25 Old 07-31-2019, 05:12 PM Thread Starter
whitewidow
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'99 WJ will not stay running. High voltage, and other issues

Seems when it rain it pours. Last week while on the way to work my 99 WJ began to over heat, luckily close to the job site. Seemed odd that I was getting no heat though. There seem to be moisture like coolant blew out by the firewall lines for the heater core. Anyways at lunch I pulled the thermostat, which was stuck closed, so I thought that was the issue. Purchased a new one and threw it in and refilled coolant. Still over heated after 10 min or so. Let it cool down, pulled the housing for the thermostat and turned it over but no coolant seemed to be flowing. This had me to believe i need a water pump so I had it towed back.

Got time today to look at it but now I have another issue. It will not stay running unless I get on the gas even then it seem like its missing a lot. Will not run at idol. My buddy kept a eye on things while I kept it running, then my 2 yr old Die Hard Platinum AGM battery began venting (over heating) so I killed the WJ. We broke out the multi-meters and tried starting again. We got readings up to 20V at the battery so we killed the WJ once more. Disconnected the alternator and ran the WJ off a battery pack which kept the voltage at 12v for a period of time but would not run at idol and seemed to be missing ignition when gassing it like before. So I started searching forums for a answer. I checked grounds on the passenger fender nothing seems corroded. Ohm between the negative terminal and the few ground points I checked were at 0 which is good. Could this be a PCM/ECU issue? If so how can I test this? Im a bit stuck now. I was running fine prior to the over heating issue.

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post #2 of 25 Old 07-31-2019, 09:47 PM
rep-tile
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Have you checked the ground point at engine block? Corrosion can also hide under the battery cable insulation near connectors. Splice it with a cardboard cutter to make sure.

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post #3 of 25 Old 08-01-2019, 06:35 AM
jtec
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Is this a great 4.0L or the v8?

Did you check for codes - the battery temp as well as 20v should have set some codes.

Fill with water for now till we find issue - coolant is expensive if opening and closing system constantly dumping coolamt. Get the Correct thermostat installed, fill bleed system and bleed again. Start and observe any coolant leaks, did it overflow before the temp gauge indicated a high temp?

A coolant system pressure tester makes this easy and safe - often a rental or loaner. Great and easy to use esp in the hot summer.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 25 Old 08-01-2019, 03:14 PM
j4bs4209333
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I had a 2000 a while back and while driving my battery gauge spiked to 19 and the speakers made the worst screeching noise ever. Hightailed it home it ran to the junkyard thinking of the alternator is no good. Alternator didn't fix it so then I'm thinking PCM. For the heck of it I decided to borrow a battery out of another car real quick and that was the problem. I've never seen anything like it before but never had problems after. Before you go any further try borrowing a battery out of someone else's car and see if that fixes your voltage issue. As for your cooling issue if it's a 6 cylinder is your fan working?
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post #5 of 25 Old 08-03-2019, 07:59 AM
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The PCM contains the voltage regulator. If it malfunctions, it could cause over charging at the battery.
Very unlikely it is the alternator but I'd take it to a shop and have it tested to remove any doubt.
Hmmm must be nice to get paid at your job to work on your jeep at lunch time..l
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post #6 of 25 Old 08-03-2019, 11:11 AM Thread Starter
whitewidow
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Quote:
Originally Posted by rep-tile View Post
Have you checked the ground point at engine block? Corrosion can also hide under the battery cable insulation near connectors. Splice it with a cardboard cutter to make sure.
Where is the ground point on the block located?

Quote:
Originally Posted by jtec View Post
Is this a great 4.0L or the v8?

Did you check for codes - the battery temp as well as 20v should have set some codes.
4.0 the daah gauge is not reading any voltage. Basically stuck a 9 or whatever the lowest reading is. I spiked to 20v on my multimeters.
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post #7 of 25 Old 08-03-2019, 11:15 AM Thread Starter
whitewidow
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Quote:
Originally Posted by j4bs4209333 View Post
I had a 2000 a while back and while driving my battery gauge spiked to 19 and the speakers made the worst screeching noise ever. Hightailed it home it ran to the junkyard thinking of the alternator is no good. Alternator didn't fix it so then I'm thinking PCM. For the heck of it I decided to borrow a battery out of another car real quick and that was the problem. I've never seen anything like it before but never had problems after. Before you go any further try borrowing a battery out of someone else's car and see if that fixes your voltage issue. As for your cooling issue if it's a 6 cylinder is your fan working?
I'm going to try a battery here in a bit. My dash guage is not reading anything. I cought the spike on a multimeter after the battery vented.

The cooling issue I will work on after if I get it running right again.
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post #8 of 25 Old 08-14-2019, 04:26 PM Thread Starter
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Battery wasn't the issue. Should I replace the PCM?
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post #9 of 25 Old 08-15-2019, 10:50 AM
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Quote:
Originally Posted by whitewidow View Post
Battery wasn't the issue. Should I replace the PCM?
the PCM is part of the list of things that could go wrong and cause what you are seeing but I'd do the easier and less costly things first. (Sorry, I don't know what all you have done but just incase, here is my list:

1. Ensure good grounds - search this site for an article a fellow did that shows ALL the jeep grounding point and pictures - that should help
2. Take alternator to shop and have it load/stress tested. (and you already checked the battery)
3. Ignore and then replace the dash voltage gauge/gauge cluster. Use a real decent quality volt meter when checking voltages. The voltage meter on my gauge cluster died and acted the same when as you describe-the voltage gauge really doesn't directly measure the voltage, it get its signal from a message on the CAN bus. What has probably happened is the gauge movement itself has malfunctioned.
4. Google PCM issues on JGC... you will find a ton of information that may suggest some ways to diagnose directly or narrow things down that it is most likely the PCM. IRC,MY 1998-2002 PCMs were prone to two types of failures: cracked traces on the PCM circuit board around the connectors, electrically undersized I/O semiconductors that would fail open. Without having a diagnostic terminal to talk to the thing, it is hard to determine if it has failed. (Maybe a local garage can test it? IMO, it is an expensive thing to take a guess on replacing. (a cheap repaired one will cost around $225, a re-manufactured one from MOPAR will cost around $425-$450). My understanding is that for this range of Jeeps, there are no 'new' ones - they are either repaired or rebuilt (rebuilt ones replace some of the components, whether or not they are bad.)
Good luck
J
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post #10 of 25 Old 08-15-2019, 11:23 AM
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Quote:
Originally Posted by whitewidow View Post
Where is the ground point on the block located?
Below is the ground write-up I did if you haven't found it yet. You can see G103 on the passenger side block in a diagram along with what's connected to it (PCM grounds). Good luck.

https://www.jeepforum.com/forum/f310...-info-4192594/

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post #11 of 25 Old 08-15-2019, 11:30 AM
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Quote:
Originally Posted by whitewidow View Post
Battery wasn't the issue. Should I replace the PCM?
I forgot to mention some things in my previous post:

Diodes in the alternator can fail and it can output a higher voltage than required. The voltage regulator is in the PCM but, if the alternator is bad, the outputs from the regulator will effectively be ignored. Worse yet, A high voltage, e.g. > 16v on the electrical system will often kill the PCM. Replacing the PCM with a bad alternator will kill the new PCM. Check the alternator first!

People have installed separate regulators in the jeeps that effectively bypass the PCM. This may be worth the gamble if you are certain that other parts of the PCM are working OK.

Some things you can try on the PCM – Remove the connectors and spray the contacts with a contact cleaner or a ‘conductivity enhancer’ such as Stabilant 22. Ensure that the PCM case is well grounded. Mine has a separate braided ground strap.
Speaking of grounds, as an added precaution, you can rum separate grounds cables from your battery to the engine, from battery to the body/firefall, but devices (such as PCM) need to have good ground connections to the firewall.

Did you attach a scanner to the PCM? If it doesn’t communicate, it is probably dead.

As far as testing/looking for bad grounds, you can do voltage drop test – described in the FSM.

Good luck
J
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post #12 of 25 Old 08-15-2019, 12:05 PM
jtec
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The gauge is not reading a voltage, could it be the PCM is not seeing the voltage it expects and ramps up alt output?

A scanner will make this a quick trouble shoot, we will see codes, and what voltage the PCM sees - compare to battery Voltage and alt output terminal...

But jumping to PCM appears consensus.

Contact "waterluver" a forum member for PCM's and assistance.

PS take him fishing.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #13 of 25 Old 08-16-2019, 09:15 AM Thread Starter
whitewidow
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Thanks guys I will check the ground points today. I just checked a couple on the fender last week.

I will pull the alternator and have that load tested as well.

I do believe this is due to the engine bay getting soaked with coolant due to it overheating. Something got wet and failed
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post #14 of 25 Old 08-16-2019, 09:22 AM Thread Starter
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I did come across this YouTube video of a 4.7 WJ having similar issues with idling and dying out that a replacement PCM solved. Although Im not noticing relays opening or closing nor a CEL popping up

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post #15 of 25 Old 08-16-2019, 02:00 PM
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Quote:
Originally Posted by whitewidow View Post
Thanks guys I will check the ground points today. I just checked a couple on the fender last week.

I will pull the alternator and have that load tested as well.

I do believe this is due to the engine bay getting soaked with coolant due to it overheating. Something got wet and failed
When I bought the 04 I'm currently driving I bought it with a bad PCM and had to tow it home. The previous owner replace the alternator twice thinking that was the issue but the minute you disconnect the jumper cables it would die. I got my PCM on eBay with the matching keys, ignition switch, locks, and skis reader for $100. If you do end up needing to replace yours you have to get the matching keys and everything with it to get a used one. I wouldn't even bother paying the price for a new one.
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