Not charging at idle

[dbcjmc]

Hi Folks!

My '77 280Z with the 280ZX alternator isn't charging at idle even after a new alternator swap. Any and all help is welcomed please!

[Zed Head]

Does it charge when you increase engine RPM?

[dbcjmc]

Yes, it does. I disabled the regulator and did the ZX upgrade. It worked fine for about 1.5 years and just quit. Replaced the alternator with a new one and charges at higher RPM but not at idle. Do you have a solution? Disable links appear OK and not getting hot.

[dbcjmc]

That should read "Fusable links" appear OK. That darn spell check!

[Zed Head]

If you got the replacement from an auto parts store like O'Reilly or Autozone, take it back and tell them you want a replacement. That's why they have lifetime warranties, because the quality of the rebuild is not very good. Sounds like you just got a bad one. I had a rebuilt O'Reilly (actually Schucks) alternator, bought it directly from the store, that put out less at idle than a ten year old, corroded Nissan alternator. The rebuilds really are just poor quality. Good luck, be emphatic that you got a bad alternator, even though it will test as "OK" on their machine.

Or get a refund, buy a junkyard alternator and have it rebuilt at a specialty shop to higher output, using better parts. Someone here will probably know of a good shop.

[dbcjmc]

Interesting. I actually had my local mechanic do the work. He said he's tried 3 different alternators all with the same result. I do like the idea of having one rebuilt by a specialty shop. Maybe that's the trick. Many thanks for your input.

[dbcjmc]

Is the wiring for the '77 the same as the '76? I can't download the '77 FSM from Xenon so have been using the '76. Also have this great color wiring diagram for a '76 that someone posted here someplace.

I'm having the same charging issue that Harwyre posted in another string and think it may be a relay gone bad somewhere. The alternator will charge after I rev the engine up to ~5K just once. Then, everything is fine. Using the '76 wiring diagram to search for a relay gone bad someplace.

[Zed Head]

For what you're looking at 76 would be the same as 77. The problem you're describing now is not the same as what it looked like you were describing in Post #1. The "L" wire, which is one of the two wires at the T plug in the back of the alternator, is probably not getting power. The L wire runs through the charge lamp in the voltmeter and provides current through the alternator windings to make the magnets that allow electricity to be produced. Does the charge lamp turn on when you first turn the key on, before you start the engine? If not, it should.

It could be that your first alternator had enough residual magnetism in the winding cores to start charging at low RPM. Your new one doesn't and needs the L wire current. You can check voltage at the L wire in the T plug with the key on.

Your mechanic really should have checked that when you told him what the problem was.

Edited October 26, 2013 by Zed Head

[dbcjmc]

Thanks so much for your help. No. The red charge light does not come on with the key on. The light doesn't come on with the key on whether the engine is running or not.

I measured voltage to the L wire, and it's only pulling a few hundred mili Amps. When I rev the engine super high just one time, then it measures about 14.5V and all is good. Do you think it's a bad alternator?

As I side note, I saw your other post about the brake check relay. The brake warning light is working like it should. I pulled the passenger seat and carpet to check. Funny thing, the brake warning light works as it should with the relay unplugged as well. No clicking sound when I connect the battery, so don't think this is the issue.

I checked the voltage regulator bypass wiring I did. It's been some time so I don't remember the source.... I checked the wiring... They're as follows:

Yellow to Blue

White/black to Blue

Black - no connect

White/red - no connect

I kind of doubt this is the issue because everything was working before the old alternator died.

I'm inclined to ask mechanic to try alternator #4. What do you think?

[Zed Head]

The charge light comes on when you turn the key to On because there is current running through it and the alternator windings. When the alternator starts charging diodes prevent the current from flowing back through the light so the light goes out (that's a super simplistic explanation but I'm no expert). The 14.5 volts that you measured after revving show that the alternator is working correctly. The fact that the charge light does not illuminate shows that no current is flowing through it to the alternator windings. It could be as simple as a bad charge lamp bulb in the voltmeter, or a bad connection before or after the charge lamp. I would trace the wiring for the charge lamp and find out why it doesn't work. That wire is key to your problem. It doesn't matter how many alternators you try, if there's no current through the L wire they won't work right.

The wiring diagram shows that the yellow wire from the T plug passes through the brake check relay. So, whatever you did to fix the brake check light must have disabled the L wire.

It's possible that somebody rigged your other alternator up as a "one-wire" alternator. I think that you can do that by just connecting the L to constant power. I'll bet when your other alternator died you had to figure out why your battery kept dying and the lights were dim, or why did my radio die, etc. If it was wired right, the light would have come on.

Good luck. I would trace the L wire first, it might just need a new wire run to the T plug.

[dbcjmc]

Thank you Thank you Thank you!!!

This little charging light was indeed the issue!

I replaced the light bulb and now it's working like a charm! Like you said, little red light on with key on, and then off when the engine is running. I'm getting 14V+ at idle now. All is good.

So.... I'm still a little mystified as to how it was behaving before said light bulb replacement. Not sure why or how I was getting a full charge only after the one time high RPM boost.

Either way, thank you SO MUCH! for your help! Another Z back on the road.

[Zed Head]

Glad it worked, you're welcome. You may have completed the fastest voltmeter removal and replacement I've heard of. And to be honest, I don't even know how to replace the charge light bulb, but I know it needs to work. Did you actually remove and replace the bulb behind the charge lamp? What kind of bulb is it?