Strange voltmeter behavior

hear

hear

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Drove the thing a ton last weekend — Dallas to Tulsa, then Tulsa to Springfield MO, wheeled 2 days, then Springfield all the way back to Dallas. So basically 14 hours of travel & another 15 hrs of trail time. Then about 45 minutes from home, a strange thing happened.

1. started squealing, which is almost certainly the belt.
2. Voltmeter on the gauge cluster went to 0V. Well, ok, it doesn't really read anything below 9, it was effectively "off."
3. The auxiliary voltmeter I have powered off the cigarette lighter showed 11ish volts, which is as low as I've ever seen it read.
4. Temp gauge started rising. The entire trip it never budged off the 210 mark, but it was now halfway between the 210 mark and the 3/4 mark. It reached some maximum around that point, possibly aided by the fact that it was in the low 50s outside and I was doing 60+
5. all other Jeep function, gauges, lights, etc appeared to be unaffected.


While this was happening, "something else" happened; I heard a pop in my speakers, my stereo rebooted and for a moment the dash voltmeter read 14 again, but it didn't last long before it dropped to 0 again.

I pulled over & popped the hood, and it definitely seemed like the squealing was coming from the area around the alternator, but everything was spinning w/o any obvious slippage. I had power steering the entire time as well. While I was stopped I kept looking at the temp gauge and it never got any higher, but it also wasn't going back down to 210.

So I turned off all my accessories (headlights [it was 2pm but overcast], radio, & heater blower) and got back on the road. A short while later the squealing stopped, the dash voltmeter showed 14V for a short while, but then went back to "0V". The engine temp went right back down to 210. Meanwhile the aux voltmeter was erratically bouncing between 13.8 and 14.4. Since I installed that voltmeter (really it's just a dual USB that happened to also have a voltmeter), it typically reads right at 13.8V while driving. Prior to this the dash gauge would always read just over 14V.


I put a Gates belt on about a year ago so I'd be surprised if it was already bad but obviously I can't rule it out. But then the squealing stopped and didn't return for the last hour of the trip. When I got it in my driveway I turned it off, and then restarted it...It started right back up and the gauge cluster read 14V again. Let it sit for 2 days and then moved it, again no issue starting and the voltmeter read 14V.


Obviously I'm at a loss for what happened, but I'm also confused as to why the 2 voltmeters would read differently. I haven't had a chance to look through the diagram yet to see how that voltmeter gets its signal; does it actually measure the voltage drop or does it get "instructions" from the PCM on what to display?

Would love to hear some ideas.
 
Check the split wire loom harness from the ECU between the valve cover and the firewall. The harness is routed near a threaded head stud that is known to rub thru the split wire loom and wiring insulation. This will cause the wiring to short to ground or to each other which will interrupt ECU and sensor communications. The gauge communications come from the ECU harness.
Check the three 32 pin harness connectors for the ECU communications to ensure they are not oxidized or loose.
 
The ECU pins are fine, just had all that apart not too long ago. I will check that section of the harness for sure. Probably need to find out what wire the voltmeter comes in on.

But also, it sounds like something is going on under the hood. It used to run very quiet, but now there is what I can best describe as a "shhhhhh" sound that feels like a bearing is maybe going out.


Drove it to get donuts today, and my aux voltmeter was reading a solid 14.4V, which it never has before. Possibly the battery was low and the alternator was working harder to charge it?
 
My bet is your serpentine belt is loose and you need to tighten it via its adjustment screw. Your '97 does not have an automatic belt tensioner as newer models have, the belt's tension is adjusted with a long screw on the power steering pump's mounting bracket.

It should be tight enough that you can barely deflect the belt 1/2" by pushing on it hard with your thumb at the belt's widest unsupported length on top.
 
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Jerry Bransford said:
My bet is your serpentine belt is loose and you need to tighten it via its adjustment screw. Your '97 does not have an automatic belt tensioner as newer models have, the belt's tension is adjusted with a long screw on the power steering pump's mounting bracket.

It should be tight enough that you can barely deflect the belt 1/2" by pushing on it hard with your thumb at the belt's widest unsupported length on top.
Click to expand...
Remember to loosen the lock down bolt before attempting to turn the adjustment bolt.
 
Jerry Bransford said:
Yep, good reminder. That is the big black bolt in front that the pulley spins around. The adjustment screw moves that pulley up/down so that bolt it spins around has to be loosened a turn or so.
Click to expand...

Is it common for it to "suddenly" get loose enough to squeal and then stop for no good reason?

Regardless, loose belt doesn't really explain why the dash voltmeter read zero while the other one read 14V. The only way it gets to 14V is if the alternator is running. I guess I need to look at that section of the harness. THAT would explain that bit.
 
Similar symptoms meant a failing alternator for me.

I believe that the voltage gauge on the dash gets its signal directly from the alternator circuit, but what your're reading from the plug-in voltmeter you've got is reading a PCM supplied signal. I base this on what I see running the Torque app with an OBD reader. The OBD consistently is in the 12V range while the dash gauge is at 14V.
 
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I wouldn't worry about 9 vs 11. It sounds like you had a really bad short and the alternator was fully loaded to the point it started slipping. I think a bad alternator could do that like @98TxTJ suggested. The pop in the speakers is a good indication something arced and was drawing a lot of current. If you blew a diode in the alternator it might make an odd whine after it's gone. It might have shorted and then basically exploded.
 
I think I found the problem. Idler pulley looks like it may have broke at the bearing or something.

I set the tension correctly several months back, but it was definitely loose when I checked it so I’m like “why would it lose tension all of a sudden?”

And now we know why.

65DA23E7-0BC7-4078-BE0F-C62D54896FD4.jpeg
 
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If it's just the bearing allot of places like Napa sell them and you can just press it in. I've done it a few times. Water splashed on the metal outside ring can crush the bearing.
 
the dust washer is all bent and the bolt sleeve appears to have worn super uneven. New one already on the way.

6BF50AE4-BB0D-4102-890F-07E6FDA2790B.jpeg
 
Looks like it wore on the mount, and even put a small groove in the pipe that connects to the heater core hose. (Barely visible behind the AC compressor). There are metal shavings/dust all over this area.


4326C295-6D0F-45B3-8DB9-F1417D2AEB2D.jpeg
 
98TxTJ said:
what your're reading from the plug-in voltmeter you've got is reading a PCM supplied signal
Click to expand...
OP described it as a "dual USB that happens to have a voltmeter" - it's certainly just reading the actual voltage it sees at the 12V socket, it's not communicating with the PCM in any way.
 
IOwnCalculus said:
OP described it as a "dual USB that happens to have a voltmeter" - it's certainly just reading the actual voltage it sees at the 12V socket, it's not communicating with the PCM in any way.
Click to expand...
Should have stated it differently. The voltage he's reading is a PCM regulated amount.
 
hear said:
Which voltage? The one on the dash, or the one on the usb thing?
Click to expand...
I was wrong. The signal to the dash gauge is from the PCM. The voltage supplied to the cigarette lighter/power port runs through a relay supplied by battery voltage. At least that's true on my '98. From the manual:

VOLTMETER
The voltmeter gives an indication of the electrical
system voltage. The instrument cluster circuitry controls
the gauge pointer position. The instrument cluster
circuitry calculates the proper gauge pointer
position based upon a system voltage message
received from the Powertrain Control Module (PCM)
on the Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the electrical system
and internal programming to decide what system
voltage message is required. The PCM then sends
the proper message to the instrument cluster on the
CCD data bus.
If the PCM message indicates that the charging
system has failed, the instrument cluster circuitry
moves the gauge needle to the 9 volt graduation on
the gauge face, and turns on the Check Gauges lamp.
If the PCM message indicates that system voltage is
high, the instrument cluster circuitry moves the
gauge needle to the 19 volt graduation on the gauge
face, and turns on the Check Gauges lamp.
Refer to Group 14 - Fuel Systems for more information
on the PCM. Refer to Group 8C - Charging
System for more information on charging system
components and diagnosis.

ACCESSORY RELAY
The accessory relay is a International Standards
Organization (ISO)-type relay. The accessory relay is
a electromechanical device that switches fused battery
current to the standard accessory power outlet
or optional cigar lighter when the ignition switch is
turned to the Accessory or On positions. See the
Diagnosis and Testing section of this group for more
information on the operation of the accessory relay.
The accessory relay is located in a wire harness
connector that is secured to the 100-way connector
bracket under the driver side of the instrument
panel, near the cowl side inner panel in the passenger
compartment. The accessory relay cannot be
repaired and, if faulty or damaged, it must be
replaced.
 
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Thanks, I hadn't bothered to spend time in the FSM once I discovered that the idler pulley was obviously the primary source of the problem. It does make me slightly sad to learn that the dash voltmeter isn't really a voltmeter, it's the PCM's representation of a voltmeter. I should't be surprised, and I'm not. Just kind of disappointed.

This must be how my parents feel.
 
Jerry Bransford said:
Yep, good reminder. That is the big black bolt in front that the pulley spins around. The adjustment screw moves that pulley up/down so that bolt it spins around has to be loosened a turn or so.
Click to expand...

I don't think I have what you describe. When you say "that pulley" I'm not sure which you mean, but the only one I have that moves is my power steering pulley (the whole pump & bracket, actually). I have an adjuster bolt that is generally below the temperature sender; loosening it relieves the tension on my belt. If there is supposed to be another bolt, it doesn't seem to be a limiting factor in all this. OR maybe it being gone is how I lost tension in the first place and the pulley was just coincidental. When I set the tension many months ago I didn't have a 2nd bolt to adjust.

Can you show me a picture of what you mean?
 
hear said:
I don't think I have what you describe. When you say "that pulley" I'm not sure which you mean, but the only one I have that moves is my power steering pulley (the whole pump & bracket, actually). I have an adjuster bolt that is generally below the temperature sender; loosening it relieves the tension on my belt. If there is supposed to be another bolt, it doesn't seem to be a limiting factor in all this. OR maybe it being gone is how I lost tension in the first place and the pulley was just coincidental. When I set the tension many months ago I didn't have a 2nd bolt to adjust.

Can you show me a picture of what you mean?
Click to expand...
Download the pdf of the 1997 FSM from the TJ Resources section and look on pages 7-31 and 32 of the Cooling System section which describes and show pictures of the belt tension adjuster.

https://wranglertjforum.com/threads...ice-manuals-fsm-technical-documentation.4618/
 
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