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Voltage Issue

S

shep1019

NAXJA Forum User
Location
Atlanta GA
My XJ is a 2000 4X4 stock 4.0L. When I start the engine when it is cold and then turn on the heater and the headlights the voltage gauge drops to about 10 volts and I get a squeak that sounds like a belt squeaking. If I turn them off the noise stops and the voltage goes back up. Turn them back on then the noise comes back and the voltage drops.

It does this until the engine warns up a little bit. A friend told me that the brushes in the alternator might be bad, but that doesnt sound right to me. Any suggestions would be helpful.
 
Got a/c? If so, it may be cycling the compressor if you have the defrost going. That will put a bit of a load on the accessory belt--the squeek/squeeling?

The volt gauge in the XJ is at the end of load, so it dips quite a bit when running electrical accessories. However, 10 volts is low--your engine management system will start screwing up if you drop below 9 volts.

I would start with cleaning your cable ends, both ends of each cable, and while you have them off measure their resistance with an ohm meter--should be near ZERO. While you are doing this would be a good time to renew the unibody grounds--battery to fenderwell and head to firewall.

With all that done and put back together, start the engine and measure the voltage between the two battery terminals--should be about 13.6~14.5 volts if charging correctly.

Post back results.
 
The dash gage is hooked on to the end of everything. You need to test with a meter at the battery.

I wonder if the electrical load is loading up the alternator enough to make the belt slip and squeel. I would tighten up the belt a little.
 
winterbeater said:
The dash gage is hooked on to the end of everything. You need to test with a meter at the battery.

I wonder if the electrical load is loading up the alternator enough to make the belt slip and squeel. I would tighten up the belt a little.
Click to expand...

X2
 
The dash gage is hooked on to the end of everything. You need to test with a meter at the battery.
===================================================================
On late models the dash gauge does not read voltage at all. It is driven by the ECU. Run the key on key off test and watch ALL the gauges read what the ECU tell them what to read.
But do clean all post, grounds as listed tighten belt as needed, check you voltage at the bat key off and with engine running. Keep in mind the ECU is also the voltage reg. It also has a battery temp sensor and when the battery gets warm. The ECU/reg will drop the alt output voltage a hair. Best to check FSM for the right reading.
 
Freshen electrical connections.

How old is your serpentine belt? How tight is your belt? Replace it if there is any question. I like to use the Goodyear Gatorback for a replacement.....The belt on the 4.0 needs to be awfully darn snug to stay quiet.
 
Cleaned up the electrical connections and it is still doing it. The belt is about 8 months old and it is a gatorback, I will try to snug it up a little more tomorrow.

I dont know if the issues are in any way related, but the AC always squeaks when you first turn it on. I dont know if that has anything to do with it but thought that i would mention it.
 
Ok, so engine running, all accessories turned off, measure the voltage at the battery between the positive and negative terminals. If not 13.6~14.5 volts, you are not charging enough.

Note: numerous reports of late model Nippondenso alternators testing good a the "chain" parts stores but proving bad when checked by a competent shop.
 
Ive checked the voltage across the battery and it is always around 14 volts. For instance, I was driving to work the other day and the voltage dropped way down and the "check gauges" light came on. So I pulled over right away and measured the voltage and it was back up to 14. The dash gauge dropped way down and then came back up by the time I pulled over and measured across the battery. I had to turn the car off and crank it back up to clear the light but it ran fine after that. It just does this when I first crank it up and there is a load like the headlights and the heater/defroster. Thanks for the input.
 
Are you near an advance auto?? They do free battery/alternator testing :laugh3:

Just thought to mention that... I like free little services like that. Every time i buy windshield wipers, I always let them put them on haha :smoker:

Good luck! keep us posted.
 
Well, your PCM controls the alternator. It is not charging intermittently, so it is the alternator or the PCM dropping out. You need to determine which before something goes out and takes something else with it--gotta love them fancy new systems!

I would call around and locate an alternator shop and have them test it. Don't rely on the "FREE" test at the parts stores.
 
So ive been thinking about this a little more. It is only doing this when the defroster and other loads are on. If I understand it correctly the defroster turns on the AC compressor. My AC has always squeaked like crazy when I first turn it on. If it starts squeaking and I turn the defroster off it stops. Also if the voltage is dropping and I turn the defroster off the voltage comes right back up.

So if this is an AC compressor issue is there anything other than the bearing that could cause this to happen (low 134A maybe). I always have to charge it multiple times in the summer. Thanks again.
 
shep1019 said:
My XJ is a 2000 4X4 stock 4.0L. When I start the engine when it is cold and then turn on the heater and the headlights the voltage gauge drops to about 10 volts and I get a squeak that sounds like a belt squeaking. If I turn them off the noise stops and the voltage goes back up. Turn them back on then the noise comes back and the voltage drops.

It does this until the engine warns up a little bit. A friend told me that the brushes in the alternator might be bad, but that doesn't sound right to me. Any suggestions would be helpful.
Click to expand...

It would appear that as soon as you put a load on the cold "fan" belt, it slips. As soon as it slips, the alternator output drops.
Start by inspecting the serpentine belt for cracks, etc, then properly adjust its tension.
 
Thanks xjbubba, I am going to check the tension and see if that solves it. The belt is in good condition so hopefully it is just the tension.
 
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