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Charging problem


Trotter's Avatar
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10-05-03, 06:10 PM   #1  
Trotter
Charging problem

I have a 1984 Nissan 300ZX that has been very dependable until lately. For some reason, my battery is not receiving a charge from the alternator. I had the old alternator tested and was told that it had a bad diode. Installed the new alternator, and still have the same problem. I bought a new battery, and also put a new belt on the alternator, checked one of the fuse links that has something to do with the battery. Iím not sure which ones should be tested. Checked the new battery with a digital multi-meter, and it reads between 9 and 11 volts while the car is running. When I raise the RPM the voltage reading drops about ľ to Ĺ of a volt.

Iíve replaced just about everything that I can think of that might be causing the problem. This is driving me nuts, is there anything else I should check? The only thing I can think of; is it might be the harness that connects to the back of the alternator. Iíve had problems with it coming loose in the past, but when I tested it for continuity it checked out fine. I plan on replacing it as well. At this point I would appreciate any help or suggestions.

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Trotter

 
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10-05-03, 07:08 PM   #2  
darrell McCoy
What brand alt did you buy as a replacement, sounds like it could possibly be bad also. I Changed 3 for a guy in 2 days. He finally bought an OEM reman.

 
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10-05-03, 07:21 PM   #3  
Voltage drop while rev'ing the engine is a sure sign that the alternator is not delivering charge to the battery.

With any multimeter, check for 13+ volts from back of alternator to a battery negavitve post.

Then, check voltage drop from back of alternator to the positive battery terminal. This reading should be .2 volts or less. In practice, it could be more than .2 volts, like .5 or so. Anything higher than that and your alternator wire is the problem.

 
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10-05-03, 07:26 PM   #4  
Trotter
I don't know what brand it is, but I bought it at Auto Zone. I installed it, had the same problem. Took it off again had it tested at Auto Zone and Napa, both tests indicated that the alternator is good.

I plan on testing it with my multi-meter tommorow. Searching through the posts here I found a post that said if the voltage is good on the alt and bad on the battery, the problem is in the wiring or a fusible link, or main charging fuse. Does anyone know where the fuses (links or main?) that are part of the charging sytem are located on an 84 Nissan 300zx?

Thanks

 
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10-05-03, 08:47 PM   #5  
mike from nj
most old jap cars have the fusible links hanging off the positive battery terminal, look down that lead a few inches if it isn't right near the end. battery acid fumes have been known to corrode these things out.


note to everyone: don't put a new alternator in a car with a dead battery, especially older import ones, it will overload the diodes and burn the alternator out (no matter how new) in mere seconds. ALWAYS charge up the battery first.

 
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10-06-03, 07:13 AM   #6  
Joe_F
Agree. Make sure the battery is a good quality one and FULLY charged.

Send back that alternator and pony up for a Nissan reman unit. Far superior and will last longer too.

Use autolibrary.org to guide you if you lack a service manual for the vehicle.

 
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10-06-03, 11:27 AM   #7  
Trotter
I looked for a fuse on the positive battery cable, but what I found was a large black cable as well as a smaller white cable. I didnít see a fuse in line, all that was on the white cable was what looked to be a connector, nothing else that I could see. There is a compartment with fusible links in it, I checked all of them, and they all appeared to be good.

I took a few readings with my multi-meter. These readings were taken with lights and blower motor on, engine a 2,000 RPMís.

Alt case to neg bat cable .02

Alt output to pos bat terminal 5.27

Alt output to frame 16.65 Ė 16.75

Any more ideas are appreciated.

Thanks

 
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10-06-03, 04:40 PM   #8  
The "connector" on the white cable.... Does it look like a black plastic pill? If so this is your fusible link. A fusible link doesnt look like a fuse per say. It just looks like a lump of rubber on the wire. According to your voltage measurements the wire or link is likely your problem. Replace the link and a large portion of the wire.
Good Luck,
Billy

 
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10-06-03, 07:22 PM   #9  
Trotter
Hmmm... I don't think the cable has what you are describing on the end of the white wire. It looks like a heavy gauge white wire with an electrical connector crimped on the end of it. There is nothing that looks like a black rubber pill.

 
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10-06-03, 07:38 PM   #10  
mike from nj
Alt case to neg bat cable .02

Alt output to pos bat terminal 5.27

Alt output to frame 16.65 Ė 16.75

Any more ideas are appreciated.

i don't know if you know it or not, but that 5.27 volts is your problem. you are losing 5 volts between the alt and battery. i would follow the charging 'fat' wire from the alternator post to the battery positive and give it a tug every here and there, make it bend here and there until you find the part of wire that is broken. the correct voltage drop should never be over .2 volts, as you will find after you fix it. look closer at the wire, the voltmeter isn't lying.

 
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10-06-03, 08:58 PM   #11  
Yep, Mike is right. The 5.27 volts is your problem area.

 
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10-09-03, 12:12 PM   #12  
Trotter
You all were right, the problem was the 5.27 reading. I found the problem; it was a bad alternator wiring harness. I drove down to the junkyard on a fully charged battery, and picked up another harness. Put it on, and it is giving the right voltage readings! Thanks for the help everybody! I'm a happy Z dude now!

 
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