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Alternator - ?

L

LOUD02Special

NAXJA Forum User
Location
North Providence, RI
So I started my XJ tonight (96, 4.0 HO, AW4, 231, 141k) and with no previous symptoms at all, the red "GEN" light pops on, and the volt meter is reading barely above the red line. I'm getting barely above 12V at the battery, haven't gotten the output reading at the alt yet (engine hot, me really tired). Is this an open and close alt case? Battery is 6 months old, terminals aren't all that bad. Usually I've known alts to exhibit some kind of noise or progressively poor performance before they fail like this. Gauge showed a hair under 14 every day until I started it tonight. Any ideas?
 
LOUD02Special said:
So I started my XJ tonight (96, 4.0 HO, AW4, 231, 141k) and with no previous symptoms at all, the red "GEN" light pops on, and the volt meter is reading barely above the red line. I'm getting barely above 12V at the battery, haven't gotten the output reading at the alt yet (engine hot, me really tired). Is this an open and close alt case? Battery is 6 months old, terminals aren't all that bad. Usually I've known alts to exhibit some kind of noise or progressively poor performance before they fail like this. Gauge showed a hair under 14 every day until I started it tonight. Any ideas?
Click to expand...

Clean the battery terminals and the cables.

Check the MAXI fuses in the PDC.

Check the voltage between the battery terminals with the engine running, no other load, should be 13.6~14.5 volts.
 
Maybe, but I wouldn't expect you to blow a MAXI doing that. They just get old from warming up, cooling off, vibration--sounds like the beginning of a dirty joke!
 
Ok, got to do some more tests. None of the fuses in the PDC were blown. Cleaned the battery terminals, no difference. Checked all the grounds I could find, the only thing I found was some oil/sludge build-up on the plastic loom of the ground lead to the starter, but the terminal itself was fine, and tight.

Alt post - 12.0 -12.1
Battery itself, while running at idle, no lights or radio - 12.0v.

I guess this just points to the alt? However, the red "GEN" light was not lit when I started it today.
 
Well, on yours the Nippon Denso alternator is regulated by the PCM. There is, I believe, a battery temperature sensor located under the battery that supplies the PCM with data to help in determining charging, so you could look at that.

Some of the chain auto parts stores testers won't correctly check the ND alternators--they will test good but can be bad.

Your battery ground lead should be to the block, the positive main lead runs to the starter solenoid.

I would have the alternator tested at a competent shop.
 
joe_peters said:
Well, on yours the Nippon Denso alternator is regulated by the PCM. There is, I believe, a battery temperature sensor located under the battery that supplies the PCM with data to help in determining charging, so you could look at that.

Some of the chain auto parts stores testers won't correctly check the ND alternators--they will test good but can be bad.

Your battery ground lead should be to the block, the positive main lead runs to the starter solenoid.

I would have the alternator tested at a competent shop.
Click to expand...

That's correct about the ground run, sorry, I had it mixed up. I'm gonna check that temp sensor tomorrow and try and get to the auto zone or advanced near my house tomorrow (closed for the day) before they close. I don't get out of work until around 4 or 5 tomorrow :( Is that temp sensor something that could pop out or is it fairly secure? I've never seen it before, but then again I've never gone looking for it either. Just in case, I located some used, lower mileage alts (on a budget) from reputable yards in RI that sell them with a warranty.
 
Though it's a bit early mileage for a Nippondenso, it's not out of range for worn brushes/bad slip rings. One thing you might to just as a test is, while it's running and not charging, take a stick or a piece of pipe and give the alternator a couple of swift raps. If it starts charging again, it's probably worn brushes. If the slip rings aren't gouged out yet it can be a pretty cheap fix and it might be worth taking it to an auto electric shop rather than replacing it.
 
Matthew Currie said:
Though it's a bit early mileage for a Nippondenso, it's not out of range for worn brushes/bad slip rings. One thing you might to just as a test is, while it's running and not charging, take a stick or a piece of pipe and give the alternator a couple of swift raps. If it starts charging again, it's probably worn brushes. If the slip rings aren't gouged out yet it can be a pretty cheap fix and it might be worth taking it to an auto electric shop rather than replacing it.
Click to expand...

I'll definitely try that, but if I remove it, I'll probably just replace it. There's lots of local yards with tons of these on hand with warranties for under $40.
 
LOUD02Special said:
I'll definitely try that, but if I remove it, I'll probably just replace it. There's lots of local yards with tons of these on hand with warranties for under $40.
Click to expand...
If you can get a good one for forty bucks, then that's the way to go for sure, but don't toss the old one unless they need the core, because if it does turn out just to be the brushes, you can fix it cheaply yourself and have a spare.

ND brushes are soldered into a holder, and you can get the holder complete, or get the brushes and solder them in yourself.
 
Update:

So I was getting ready to take the XJ to autozone to test the alt, and figured let me bang on the casing before I go. I give it a whack with a spare windshield wiper arm I had in the hatch, and fire it up. Shoots right up to normal. 13.75 at the alt post, and 13.69 at the positive battery terminal. I guess I should take this as the "warning sign" to buy a new one within a week or two.
 
LOUD02Special said:
Update:

So I was getting ready to take the XJ to autozone to test the alt, and figured let me bang on the casing before I go. I give it a whack with a spare windshield wiper arm I had in the hatch, and fire it up. Shoots right up to normal. 13.75 at the alt post, and 13.69 at the positive battery terminal. I guess I should take this as the "warning sign" to buy a new one within a week or two.
Click to expand...

Well, I would go with Matthew Currie's advice and if you don't need it for a core repair your current one for a spare.
 
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