Intermittent Alternator

[danmartinic]

Thanks for the info on the Nissan alternator. I'm ok with the stock unit; no bigger turbo or pipes here. There seems to be a lot of stock rebuilds out there including an official one from Bosch (AL170X).

I finished changing the voltage regulator. I had to take the alternator out. Thankfully, I busted the duct mount hole on the one side you can't reach so I didn't have to pull the cooling parts; the alternator comes out fine if you leave the duct behind lol

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As time is important to me, I sourced a voltage regulator that is in stock at the place I buy parts from nearby. It is an aftermarket version of the Bosch original. It is clearly not as well made.

I replaced the regulator. Wow.. those original brushes are quite worn out

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Put it all back together and.... mixed results. Just went for a test drive.

On startup, I get lots of volts.. 14.5v at idle measured with voltmeter at battery. However, when I crank the HVAC fan to 4, I get a drop to low 13v / mid 12v. I am guessing this drop as I was driving and my in-dash meter shows 12v; I know it reads low. Nevertheless, the drop is big.

After this drop, if I turn off the HVAC fan, voltage does not bounce back up unless I rev the motor. This revving bounces the in-dash meter back up near 14 where it stays. Not sure why revving the motor gets it to "switch" back like that (ie. not a gradual movement based on rpm but like a switch back "on")

I also notice a distinct squealing sound when putting a heavy load (such as the HVAC fan above). This squealing is intermittent but it occurs almost every time heavy load is started.

Am I correct to assume a completely rebuilt alternator is in the works here and that simply chaning the regulator / brushes doesn't cut it? Or, is this just the behaviour of a very cheap made knockoff regulator?

At least I'm back on the road and my wife can have her car back. It's been a rough couple of days LOL!

[usury]

Is the squealing under load belt squeal? If so, that indicates the belt is slipping and provides an explanation for the reduced voltage readings at least. I think the belt tension is 80lbs, which seems like a lot.

Also, is there an instrument panel bulb that is part of the feedback circuit for the alternator? Or am I thinking about early vs late? (Or another car entirely?) If that bulb is burnt out (or replaced with an LED) the alternator won't charge properly.

[danmartinic]

Solved.. I think! Renaissance Man, it appears you nailed it.

I woke up in the middle of the night... sweating profusley.. dreaming of all the nuts and bolts I put a wrench on over the past two days... then it hit me: I forgot to tighten the AC mount bolt.

I went out and by the light of flashlight, I jacked the car up one side, removed the driver's front wheel, and somehow, between the alternator cooling duct, AC pulley, and belt, managed to tighten down that bolt. Note: there's exactly room for three clicks on the ratchet lol

This morning's drive to work showed relatively steady volts between 1/2 and 14 on the gauge. No squealing. No sudden and violent dropping.

Funny thing is that I only cracked the AC mount bolt a bit, maybe three or four quarter turns of the ratchet, just enough so the compressor can move and swing to allow belt mounting.

I guess it's enough to throw off the belt tension or alignment

FYI the belt itself is not too tight.. and it's still super old. I ordered a new one which should arrive in a day or two.

[usury]

Nice catch on the loose AC mounting bolt. Amazing how the smallest of things manifest, isn't it.

[cda951]

@danmartinic , I agree with others here that the voltage regulator is the most common failure point of the typical alternator of this era. The only reasons to replace the entire unit are if it has noisy bearings, or if a diode fails---the pole pieces and stator windings rarely have issues.

Though I now sometimes wish I had retained A/C in my '86 951, one advantage of the factory A/C delete is the alternator is mounted lower, which makes changing the voltage regulator a 10-minute job

[danmartinic]

Though I now sometimes wish I had retained A/C in my '86 951, one advantage of the factory A/C delete is the alternator is mounted lower, which makes changing the voltage regulator a 10-minute job

Where I live, AC is not required but a couple of week's worth a year... and at the moment, it doesn't work anyway! I am seriously considering the AC delete.

Changing out the regulator with the integrated brushes should be a regular maintenance item. Strange I never heard of this before. I should have changed these out as a routine about 100k ago lol

[danmartinic]

What else is really "routine maintenance" for a car over 300,000kms? What else am I missing that will strand me on the next road trip? I still have original rod bearings. Is this something I should just do?

[usury]

I just did rod bearings on my 250k mile 944na (so ~400,000 km). They showed only minor wear and the crank was absolutely pristine. Unless you've had oil pressure problems or obvious rod knock or poor/unknown oil change practices or obvious metallic glitter in the drain oil/filter, you probably shouldn't worry too much.

Fuel pressure regulator and damper have a service interval of 80k miles if I remember correctly. Those can leak and/or strand you.

If you have rubber fuel lines that cross over the exhaust headers, those will eventually burst and spray pressurized fuel into the hot exhaust. Not routine maintenance so much as fire prevention. And not so much strand as burn to the ground.

[danmartinic]

What constitutes oil pressure issues?

Car showed 69k US miles at purchase.. never had the 5-and-over showing on the gauge.

My gauge behaviour has been pretty consistent all these years: it shows no more than 4 at startup.. drops to between 2-3 fully warm... sometimes, with thinner oil, gets to a hair under 2 at idle. I can get it to 4 @4000 rpm which is factory spec but frankly, all the 944/951s I've seen show well north of what I've ever had showing

When I did the clutch, I used a dial gauge to check crank end-play or lateral movement and it seemed to be near the limit. Can't say how accuarate that is; pretty hard to do lying under there outdoors in the winter no less.

Congrats on the high mileage! We should have a "over 300k kms section" with info specific to cars driven regularly. I often feel there are specific issues vs. cars that sit (which have their own different issues)

[danmartinic]

PS.. I am ashamed to admit I still have the original fuel lines. It's always a "next spring" job

Damper is also original but fuel regulator is newer as I run 3psi with A-Tune