Overcharging 260Z

[Tank.]

I’m working on a friend’s 260z, it’s all original except for the radio which was recently installed. He had the alternator replaced at a local shop and has been experiencing some weird things of which some were not related. But it was over charging (up to 20 volts) and ended up cooking the battery. The alternator turned out to be bad and didn’t look like the original anyway. So I replaced it with a rebuilt hitachi (don’t know the part # because it’s not even listed as a hitachi) that looks correct. Also grabbed a new voltage regulator just in case. So it has a new alternator, new voltage regulator, and is still experiencing overcharging from 16-18 volts with no load, 13.8 with a full load (AC, fan, headlights, etc.). I have tested the continuity of the wiring harness side grounds of the voltage regulator and it is all good there. There is continuity with “F” and the capacitor below the voltage regulator so that appears to be all good too. At this point, I have no clue what to check, any advice/direction would be appreciated! 

 

 

[Tank.]

I also tested the sensing wire (white/black stripe) at the alternator and it was seeing 15.5 running. And there is continuity from the alternator to the voltage regulator (yellow wire) so all good there as well. 

[thisismatt]

What's the voltage from B+ to engine block?

[datzenmike]

Look at the last thing changed before the problem started... 'the alternator was replaced at a local shop'. Replacing it based on 'it looked correct' is just as bad.

 

 

There are internally regulated alternators on all '78 and up Nissans. Usually if an internally regulated alternator is put into a vehicle with an external regulator it won't shut off with the key. But it sure as hell won't work right either. Check that you do have an externally regulated alternator.

 

 

 

Today's rebuilt and after market build quality is absolute SHIT. There is an excellent chance that you could get 2 or 3 alternators in a row that are 'bad in the box'. A dealer alternator is probably close to $400, so you get exactly what you pay for with a $60 rebuild. 

 

It's a hard lesson but just because it's 'NEW'  it's absolutely no guarantee that it any good.

 

 

[Tank.]

21 minutes ago, datzenmike said:

Look at the last thing changed before the problem started... 'the alternator was replaced at a local shop'. Replacing it based on 'it looked correct' is just as bad.

 

 

There are internally regulated alternators on all '78 and up Nissans. Usually if an internally regulated alternator is put into a vehicle with an external regulator it won't shut off with the key. But it sure as hell won't work right either. Check that you do have an externally regulated alternator.

 

 

 

Today's rebuilt and after market build quality is absolute SHIT. There is an excellent chance that you could get 2 or 3 alternators in a row that are 'bad in the box'. A dealer alternator is probably close to $400, so you get exactly what you pay for with a $60 rebuild. 

 

It's a hard lesson but just because it's 'NEW'  it's absolutely no guarantee that it any good.

 

 

I can’t speak to the local shop that replaced in the first place…but it could have certainly have been an internally regulated alternator that they installed. And the one they installed wasn’t working, it was reading 8.5. Which according to the service manual, anything below 12.5 is no bueno. The alternator I installed (pictured above) seems to be working, it reads above 12.5. 

 

I should also add the ammeter seems to working as well. And thanks for the tips, much appreciated.

Edited August 7, 2021 by Tank.

[Tank.]

36 minutes ago, thisismatt said:

What's the voltage from B+ to engine block?

Which is B+? I have A, E, F, N. In this case, would you be referring to A? Thanks!

[thisismatt]

30 minutes ago, Tank. said:

Which is B+? I have A, E, F, N. In this case, would you be referring to A? Thanks!

 

Battery positive to engine block voltage when off & running.

[Tank.]

1 hour ago, thisismatt said:

 

Battery positive to engine block voltage when off & running.

Hah, yeah it’s 16.7 running, 12.7 off.

[banzai510(hainz)]

 a over charging means the alternator is good. But the regulator is bad or

or a Internat volt reg Alternator  with a external volt reg  installed msot likely

 

 

I keep my old volt regs and install them and see what happens.

 

Im not a z car guy but I ck all my fuses and connections  in case a wire went open (Like a sense line and it trys to over volt) bUt like i said Im really kind of guess on this.

I had Echlin Brand Voltregs from Napa and they were junk. over volt in 2 years

[Tank.]

2 hours ago, banzai510(hainz) said:

 a over charging means the alternator is good. But the regulator is bad or

or a Internat volt reg Alternator  with a external volt reg  installed msot likely

 

 

I keep my old volt regs and install them and see what happens.

 

Im not a z car guy but I ck all my fuses and connections  in case a wire went open (Like a sense line and it trys to over volt) bUt like i said Im really kind of guess on this.

I had Echlin Brand Voltregs from Napa and they were junk. over volt in 2 years

 

Yeah I have 2 voltage regulators and tried them both, same result. I think this is a rabbit hole I don’t have time to go down so my friend will most likely have to get this looked at by an old timer - Rock Vest.

[banzai510(hainz)]

If one has a O scope one can see if you have a unregulated Over volt condition. Mean your alternator is good. but regulator.

 

I went back to tthe old Japan made regulators. as I had a issue with my 521 where the alternator woul pop my solid state volt reg.  I out a different alt and got a mechanical Volt reg.