Diagnosing a problem or two

[crumbscomanche]

Good afternoon Comanche Club,

 

I am trying to diagnose a couple of problems, which I'm hoping are symptoms of the same thing. The first problems began late last week - the voltage meter took a dip down to the red on a fairly new battery (a Duralast battery from the PO dated 4/17) after staying pretty much dead center since I purchased the truck in June of this year. It made sense because we had left the radio on for a few hours while working on the suspension.

 

Fast forward to a pretty rough trail ride Saturday. I had a couple of problems out in the desert, and noticed for a little while the tachometer stopped working, and the voltage meter dipped down even farther. I thought the latter was odd, because I would've figured the battery would've been recharged after driving for several hours. As we were pulling out of the Rec Area, the check engine light turned on. 

 

The tachometer came back to life after about 20 minutes on the highway, but the voltage stayed low and the check engine light stayed on. After rinsing down the truck at the car wash for 10 minutes, the battery died, and could not be jumped. I decided to pick up a yellow top Optima, since it was on my list of upgrades this year, and hoped this would fix everything, but alas it did not. The truck is having no problems starting up, but the check engine light remains on and the voltage counter very low despite the brand new `battery. 

 

Right now I'm thinking it's the alternator or a fuse for the voltage sending unit, but the alternator was replaced in the last 12 months by the PO. If anyone had any thoughts or suggestions on where to dive in, it would be a huge help.

 

Thank you in advance!

 

Voltage Counter as it sits with the yellow top: 

 

 

[Marine1Texas]

I would check your grounds. Under the dash grounds. I would also check the wiring on your fuse box. If you have the c101 connector box I would make sure everything is good there too. I deleted my c101 box because of the faults that can and did happen with it. With voltage meter check after the fuse link that come from alt.

 

I know for a fact if your ground under dash is bad, that voltage guage will read low. My guess is that you have some loose connections under dash, possible in c101 box or like you said a blown inline fuse that come from allt. Since you said it cut out then tac came back.

 

Either get voltage reader or take to auto parts store to check your alt. read out. I have a battery charger that detects the voltage and amps from the alt. then you can get a extender and check the back of alt to battery while it is running.

 

 

[crumbscomanche]

@Noriyori_Kudo thank you for the info. I thought about that too, since I ran it pretty rough on Saturday and I'm sure something on a 513k mile truck could've been knocked loose.

 

What would indicate the the C101 box and would the under dash ground be located near the fuse box to the left of the pedals? 

 

Thanks again. 

[gogmorgo]

Check for codes

I'll bet you'll get a 41. In my case it was bad battery cables. But that'll help you out on the check-engine light. 

You can use a voltmeter on the battery terminals to confirm the guage reading. My guess is your dash isn't grounded well, leading to it reading low. It's not uncommon for that to be a problem. But it can't hurt to check the fuses in the panel under the dash. 

Also you don't have a C101, that's Renix junk. Is yours a 91 or a 92?

[hakukamana]

Pull the instrument cluster fuse, either replace it or clean the terminals. Had a low guage reading swapped out the fuse dead middle on the voltage meter. The dying battery, check your battery charging with a voltage meter to verify that the alternator is doing its job. At start up you should be 14+ and charging. A high 13 would be acceptable, if its below 13 your running off the battery not the alternator.

[Green Mesa XJ]

For the alternator voltage I had the plug on the gm style alternator be faulty, wiggled the plug and the alternator would suddenly start charging . Since swapping out my 1985 harness the alternator works all the time.
I think the renix jeeps still uses the gm style with built in regulator, if so the plug may be bad. But with the other symptoms I’d check the voltage with a tester then start working backwards to the cause, bad ground, c101, fuse box, alternator, something along those lines.


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[crumbscomanche]

@gogmorgo thanks for the link. I will check codes and report back tomorrow. It is a 91. I should be able to get a voltmeter for a test too. 

 

@hakukamana I will make sure I do this regardless, thank you for the tip.

 

@Green Mesa XJ Seems like the consensus is some faulty connection! Thank you for the feedback. 

[Green Mesa XJ]

Oh its a 91 MJ? That’s a different, it’s a Japanese alternator with the voltage controlled through the pcm.
Still could be a bad ground or battery cables, fuse box/fuse, possibly cluster.

Still I’d start by verifying the voltage, might just be the alternator, but when it fails there should be a check engine light or maintenance maybe. As I remember it the 91 has two lights, one is the emissions (o2 sensor I think), the other when a code is triggered. When the alternator started to fail that Check engine light did trigger.
The 02 sensor/emissions light was some proprietary chrystler crap so the light could only be rest at the jeep dealer, most long term owners annoyed by it pull the bulb to it.

I missed where it was a 91, most of what I said about the gm alternator doesn’t apply.
500k mikes guess you can write to jeep to get a high milage club license plate bracket, if they still do that program.



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[Green Mesa XJ]

Oh, check the fuses in the box by the battery, huge 60 amp(90?) fuse is for the alternator, if it pops the fuse for some reason you’ve got not alternator charging. Ours did this when Firestone messed up the battery cables one of the times we had them try to fix the loose steering. I cleaned up the cable connections, one of which was a aftermarket generic style where the battery cables leads are clamped together on the positive side. Once it was squared away it didn’t blow the big fuse any more.


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[HOrnbrod]

As stated by gogmorgo - check for codes first. You have a 91 - always do that first with any problem that's not immediately obvious. It's a great tool for diagnosing, and also for preventive maintenance. Codes should be checked every month or so even if it's running great.

[crumbscomanche]

update - alternator was bad. I was traveling this week so I dropped it off at the shop for a replacement, so hopefully I'll be back in the dirt shortly.