Alternator or Fusible Link Problem?

[nhines3]

Hey guys, new member here, owner of a 78 280z for 5 years now. I ran into a problem that I need some help with. I've been having some electrical issues with this car since I purchased it. I'm nominally knowledgeable about vehicles to begin with, but I want to learn more. The problem Im having is that the battery isn't getting a charge or full charge from the alternator. I took it in and had the auto parts store check the alternator (while in the car) and the guy said it was sending 11.46v but only 30 amp output. He told me to clean up the terminals before replacing the alternator. Not that they really needed it, but I did so anyways. By the way, I myself replaced the cables just a few years back, so I know that is not the issue. I did what he said and it still wont charge the battery. Last time I went out in checked the car wouldnt turn over, it only clicked. Ive had that problem before so I jimmied with the fusible links and tried again. It actually turned over instead of clicking but there wasn't enough juice to get it started. So what Im wondering is if I should replace the alternator or replace the fusible links. Im not sure if fusible links would be the culprit to the battery not charging or not (since I don't know jack about electrical), or if this simply is an issue of a bad alternator.

Thanks guys and its great to be a part of a community of fellow z car lovers.

Edited May 6, 2011 by nhines3

[SteveJ]

First, download a copy of the FSM. You'll find it in the links below.

Second, look through the engine electrical section. It goes over how to diagnose the charging system.

Now, having said that, 11.46 volts is too low. Was the engine at idle? What is the voltage at 2000 RPM or higher? (Again, look at the FSM for the specs.)

As for the fusible links, they are available at Courtesy Nissan. Some people like replacing them with maxifuses, but I haven't found satisfactory answers as to the true ratings of the fusible links, so I'm not sure what maxifuses would be appropriate. It's not a bad idea to replace links and clean the terminals with something like Caig deoxit. (You can find it at Radio Shack or from lots of online vendors.)

[240260280z]

Measure a battery in the morning with a volt meter:

12.0V dead

12.8V fully charged

yep 0.8V range.

Next start your car and let it idle then measure the voltage on the battery. It should be ~ 13.5V to 14.5V. This is a charging voltage from the alternator. If the voltage is lower then this then your alternator/voltage regulator may have a problem or the fan belt is loose.

[nhines3]

First, download a copy of the FSM. You'll find it in the links below.

I have a paper one that I was able to find finally.

Second, look through the engine electrical section. It goes over how to diagnose the charging system.

The problem is that I really don't have much of a clue when it comes to electrical diagrams.

Now, having said that, 11.46 volts is too low. Was the engine at idle? What is the voltage at 2000 RPM or higher? (Again, look at the FSM for the specs.)

I took it to the auto parts store and they checked it. The car was at idle during the test. I could go down there and test it again but at this point I'd rather just take the thing out of the car and allow them to bench test it.

As for the fusible links, they are available at Courtesy Nissan. Some people like replacing them with maxifuses, but I haven't found satisfactory answers as to the true ratings of the fusible links, so I'm not sure what maxifuses would be appropriate. It's not a bad idea to replace links and clean the terminals with something like Caig deoxit. (You can find it at Radio Shack or from lots of online vendors.)

Thanks for the help here. I like the idea of keeping some of the stuff as original as I can. Mostly everything under the hood is original with the exception of a performance coil that the previous owner put in.

I guess I can try cleaning up the fusible links and take the alternator in for a bench test.

[nhines3]

Measure a battery in the morning with a volt meter:

12.0V dead

12.8V fully charged

yep 0.8V range.

Next start your car and let it idle then measure the voltage on the battery. It should be ~ 13.5V to 14.5V. This is a charging voltage from the alternator. If the voltage is lower then this then your alternator/voltage regulator may have a problem or the fan belt is loose.

Thanks for the suggestions. I'll give those a try. The battery is relatively new, I bought it last summer a month or two before I garaged the car for the winter. After bringing the car out of storage, it has been running fine for a few weeks (right up until monday when this problem started occurring). I say all that because I don't believe the battery to be the issue since it is new and will take a charge from a trickle charger. I'll give it a check anyways though.

[Zed Head]

Check voltage right at the alternator positive wire with your negative probe on the case, then check at the battery terminals, to see if it's the alternator, or the wires and connections. You might get over 14.5 volts at the alternator, since the regulator is regulating to what the S wire sees.

The guy at the auto parts store should have done that - one, to determine where the real problem is, and two, to sell you an alternator if yours is bad. He might have been just following a standard procedure though.

Edit - you should take measurements at idle and higher rpm also, about 2000 RPM should give full charging voltage.

Edit 2 - Reading your first post, maybe the auto store guy was telling you that the alternator is bad, but your terminals are dirty also? Either way, confirming where the problem is won't hurt.

Edited May 7, 2011 by Zed Head

[nhines3]

Went to pull the alternator so I could have it bench tested and the stud that comes out of the alternator that sends power to the battery was so rusted that it broke off under very little pressure. Also, it sounds as if the bearing was on its way out anyways. I ordered a new one and it will be here Tuesday. In the meantime I got some deoxit and cleaned up the fusible links. I hope after all this the problem will be fixed.

[SteveJ]

Make sure you ordered an alternator with an internal voltage regulator (78-83). Sometimes the parts stores get it wrong.

[nhines3]

Make sure you ordered an alternator with an internal voltage regulator (78-83). Sometimes the parts stores get it wrong.

Yup, we're good to go.