Topic: Low Voltage and Gauge Problems

[JC93YJ]

Question for everyone, on Saturday I was going down the highway and the check engine light came on followed by the voltage and oil pressure gauges bouncing around.  Pulled over and I got the error code for alternator overcharging. I just put the alternator in about a year ago, and I haven't had any issues with it and the belt is only a few months old so I ruled those out. Get back on the road and the light comes back on, same code, but the gauges aren't bouncing around.  Start the Jeep back up and it's fine, no more check engine light and the voltage gauge is only reading just under 14.  I checked the voltage on the battery with the Jeep off and it's around 12.6V. Fast forward to this morning and I notice the temp gauge acting funny. The Jeep always ran on the cold side, it would barely touch 210 and the needle would drop down to the next line. Tis morning it would hover at 210 and go past it slightly before dropping down to the next line. And this was just cruising around at 60mph with an air temp of 50*. The volt gauge was also reading low, the line under 14, and that was with just the heater on. I shut the heater off and the needle went up a little and wiggled back and forth between 14 and the lower line. Oil pressure needle was also wiggling, but that sender needs to be replaced as it's slowly weeping.  Any advice would be greatly appreciated, the Jeep has never acted up on me until now. The battery is almost 5 years old, so that probably needs to be replaced. Thanks in advance.

Joe

[Jeffy]

I'd check for a loose connection somewhere.  Could be on the alternator or battery.  Make sure your chassis ground is attached.

[JC93YJ]

Okay, I checked all the connections and the grounds and they're all clean and tight. I load tested the battery and it passed, and the alternator is good. I did notice that the voltage gauge wiggled a little when I jiggled the ignition key, so I'm thinking maybe the switch. If not, is there a way to test the voltage regulator in the PCM?

[Jeffy]

Well, you have three different gauges fluctuating.  That makes me think there's a ground issue unless you have three separate issues happening all at the same time.  Did you check the gauge harness?  Ground issues can be anywhere and do weird things to unrelated systems.

[JC93YJ]

I swapped out the ignition switch, which was a royal pain, and that seems to have solved the issue. The temp gauge still floats a little bit at 210 every once in awhile but that might just be the gauge getting old. The dash harness is in pretty sorry shape, there’s stuff dangling and cut everywhere from the PO, so hopefully my spare harness goes in this winter along with the hardtop harness so I can finally use the rear window defrosrer and wiper.
The gauge harness is grounded through the radio harness, correct? That’s the only ground I was able to find under there.

[Jeffy]

Just off the top of my head there's a ground that attaches to the firewall over the throttle pedal.  You'll also want to check the connector behind the gauge cluster.  Keep in mind that when YJ's leak the water usually pours down onto the back of the gauges.  Also, make sure the traces on the plastic circuit are clean and unbroken.

[dwtaylorpdx]

The ECU drives the alternator,,, If the ALT control circuit is getting tired, it may be miscontrolling the alternator.. Check the small wire connection on teh alt, mine needed a new connector a few years back (94 YJ)

[JC93YJ]

I pulled the dash apart again and all the connections were tight and clean. All the grounds are good. I put a new oil pressure switch in and the gauge read correct again for a day. Then today on the way home the voltage dropped below 14 and all the gauges acted up again. Now the gas gauge is reading a quarter tank low, and I know it’s full because it takes 8-9 gallons to fill it from 1/4 tank, and I just put 8.5 in. If I rev it to 3000 rpm it started to go above 14 and as soon as I let off it drops again. When it goes above 14, the gauges start to act more like they used to. I checked the voltage on the battery and it was reading between 13.5 and 13.7 volts running. And 12.7-12.9 volts off. Any ideas, I’m beginning to question the alternator now?

[JC93YJ]

I checked the voltages again this morning. With the key off, I had 12.7V at the battery posts, 12.7v at the top terminal on the terminal on the alternator, and nothing on the bottom three where the black box is. Key on, voltage dropped to 12.3v at th posts and top terminal, still 0v on the bottom three. Started the Jeep and the gauge passed 14v and then dropped to below 14, at the battery it was between 13.7 and 14v, same at the top terminal on the alternator. The wire coming out of the black box had no voltage still, and the two ring terminals on the top of the box had 10v.

[JC93YJ]

I also load tested the battery and it checked out okay. After the belt dried out from the rain I listened to the alternator and I could hear a slight whine, but when I checked it with the stethoscope, it sounded fine.
Now I’m confused, I just shut it off and started it twice and both times the voltage went right up to 14.7v like it should and all the gauges acted right, and there’s no whining.

[JC93YJ]

New development, the voltage dropped again on the way home. I shut it off and went to start it and now it won’t start. The starter just clicks. When I turn the key, the temp gauge drops to 0 from it’s actual temp and the oil pressure gauge spikes. Any ideas?

[Jeffy]

The starter clicking means it doesn't have enough voltage and only the bendix is moving.   I forget if you mentioned if the battery was load tested or not.  Have you tried borrowing another battery and seeing if it still acts up?

[JC93YJ]

I load tested the battery right when all of this started and yesterday morning and it passed with no issues. I haven’t tried swapping batteries yet. The voltage drop wasn’t excessive when I was trying to start it last night, it looked about the same as always.

[JC93YJ]

Okay, we load tested the battery three times and it kept checking out in perfect shape, put the battery charger on it to see if the voltage was just low and it had a full charge, tried to jump the starter with a screw driver and it refused to turn the engine over. The fuel pump clicks on, and all the lights work, radio works, and the voltage is good. My dad tossed the load tester on the battery and switched it on and it sucked it down to 6v...amps, one of those. Tested the battery and it was still good, so we're thinking it might be a bad battery cable.  The cables look to be original and we already put a new clamp on the negative post because I cracked it a few years ago trying to tighten it because the lead was so old. Does anyone know how the positive wire coming off the battery connects into the fuse box? I have a spare harness I can take apart but I'm not home at the moment and I figured I'd ask the higher powers on here. 

Joe

[Jeffy]

The small 6awg wires goes to the front of the PDC while the 4awg goes to the starter.