pilot1

this is exactly what is happening to me with an alt which had been rebuilt by the best in my city after only 2 hours of driving!!! My alt was almost dead so I had it rebuilt, car ran perfect for 2 hours, would hold good charge with a full load (13v with all acc switch on at idle) after a hard drive up the mountains and on the gentle cruise home the volts became erratic, sometimes holding 13.8, dropping to 13, 12.8 back to 13.8, high beams on and the volt drops violently down below 13, then bounce back to about 13.2 then lower, then drop to 12 with the thermo fans on. I'm at a loss as to what could be causing it. any help.

ehall

yours, in that specific senario, may just have been a slightly under tensioned alt belt. The rest of my system is all tested and good, and I had a similar occurence aftere a long hard drive. I think it just got hot and expanded a tad more than I needed. After cooling it was fine.

pilot1

well today in melbourne it was 45deg C and I had the same problem, except today i got a horible squeeling from the alt but it was different to the usual noisy loose belt, plus today the revs were even more erratic at idle. If i rev the car 200rpm higher than idle (to 1000 or even 1100 rpm) and let it off the revs drop to 0 on the tacho (probably 50-100rpm)the volts drop to 10v and then it bounces up and does this a few more times before it settles... i really am sick of this stuff happening, I will try the belt, I know I keep posting this but I'm just so desperate to get back the car i had for 2 hours last nite, I'd missed the sort of performance that I had.

pilot1

the belt is very tight now and once again the alt worked well for a couple of hours but then it completely died and cant keep up with load... my stereo cuts out when i put the high beams on, the volts intermittently drop below 10v when adding accessories. I'd say its the alt but it cant be, i just had it fully rebuilt 2 days ago. plus without load its maintaining a steady 14v, however when load is reduced it spikes well above 14 possibly as high as 16v. Any ideas? This alt has also been moded with a new volt regulator which is supposed to be better than the original.

Zero10

Have you looked into the wiring? It does sound like a wiring problem.
As far as 'normal' goes, upon starting, my voltmeter will read close to 14 volts, but once the battery is charged up, and everything has been running for 20 or 30 minutes, it will usually drop down to 12.5V. I went through everything, and finally decided this is pretty normal.

JET951

hey matt, i would definatly do an amperage check. to see if anything is draining your battery when the car is off. we see a lot of aftermarket alarms draw huge amounts like 0.1 amps and above. with the car off and all dors closed (and alarm on if you have one) the amperage should be a maximum of 0.02-0.03 amps.

pilot1

yeah, I noticed that the voltage dropped after a while and accepted this as normal due to completing the charge on the batt, but the large drops and spikes in volts when adding or removing of load due to accessories is what worries me... and it only happens after a while of driving, not on start up... plus after shutting down the engine i tried replicating it for my dad and all i could achive was small drops and spikes, still abnormal but nothing like what i had been noticing.

pilot1

I read that 944's have 2 voltage regulators, since the one on the alt has been replaced is there a possibility that the second one (if it exists) could be faulty? I know when the problem isn't present and i increase the load on the system i hear something on the pas side click as the load is introduced...

thanks for any help, its all helped so far.

Charlotte944

I've had some similar issues with my 951. I knew the alternator needed to be replaced because the slip rings had some fairly deep grooves from brush wear, and the voltage regulator brushes were very close to the wear limit. The starter was also giving me fits.

I finally 'bit the bullet' and replaced the battery, alternator and starter. When I put everything back together I used Diaelectric Grease on the starter and alternator connections, and I made sure the battery cable connections were clean, tight, and covered with Battery Anti-Corrosion compound. I also cleaned the battery box and made sure that all of the electrical system ground points were clean, tiight, and coated with diaelectric grease.

Since then, I have noticed that with the engine running, the in-dash volt meter starts out near 14 volts and it NEVER drops below 13 volts. Before this, the meter would start out at about 13.5 volts and would drop to about 12 volts.

So, if you are certain the alternator is working properly, check every thing else, and pay particular attention to the battery. HINT: If the battery is more than 3 years old, it may be time to replace it.

Finally, unlike some cars that I have run across, there is only ONE voltage regulator. Some American cars used to have voltage regulators for the gages.

pilot1

the thing is my volts arn't just dropping and staying low... I'm making great charge and continues charge under load while the problem isn't pressent, once the problem pops up (usually after about 20-30mins of driving) then i get erratic voltage, not just low... the volts move up and down as the indicators flash, the engine cuts out (if only for 1 stroke) when i turn the high beams on as well as the volt gauge reading 0 and my stereo cutting out and the interior lights switching off... I get the same thing if i load it up with anything as equally powerful as the high beam (say demister). Thats where the problem lies, that its not something i see from start up to shut down, its never there on start up it always takes a little while before it happens.

nick

Zero10

I'd bet it's in the wiring. Most likely the connection at the starter motor, possibly the wiring itself has begun to rot as well.

PEvans

Resurrecting an old thread as it seems related. For me the voltage on the dash gauge is fluctuating much more than usual, from under 12V to almost 14V. On high RPM or load the voltage goes up, and recently the charging indicator and main alert light come on. My shop says the charging is working fine, but this clearly is not right.

Are there grounds I should check? Or should I just blame the voltage regulator and replace it?

mahoney944

I'd recommend looking into the Nissan alternator mod . The stock charging system just sucks, my car stays at 14v always. It's a lighter, smaller, higher out put alternator with much better cooling and yet works with all factory wiring, and at a cheaper price to boot.

Tom M'Guinn

If the shop thinks the charging system is working ok (???) then I'd be inclined to attach a volt meter directly to the battery and monitor it in the car as you drive to see if it and the gauge match. If they do, then I'd say your shop is wrong. If the volt meter shows that the voltage is actually remaining strong, despite the gauge, then I'd look into the gauge, its grounds, football connectors, etc.

PEvans

I should have added that also new is loud high-pitched RF noise when I go under a bridge with the radio on. I can connect a meter as Tom suggests. My thought is the alternator is gradually failing. I have read here for years about the Nissan mod, and I guess Bosch rebuilds are not what they once were. It's a thought, but I guess it is not trouble free either.