Rebuilt alternator installed - funny stereo behavior...

[tedder]

For my 86 carrera, my alternator failed about a month ago and after some dilly-dallying around I had it rebuilt locally at a place (Hub Automotive Rebuilders in Ipswich MA) recommended by my local Porsche mechanic (Autobahn in Danvers MA).

I put it in myself and it seems to be holding voltage and doing its job appropriately (voltage steady at 14.4-14.6 from 1500-3000 rpm tested at the battery).

All proud of myself for the first significant work I had done myself on the car since I bought it so I took it out for a spin. Drove fine, radio off, perfect day.

But then, getting on the highway, the radio seemed to emit a brief (<1s) burst of static at about 1/3 volume. The radio was off. Getting off the highway on the next ramp same thing happened. Drove home, still seemed OK otherwise. Driving it again on Sunday, coming off the highway on the ramp again I heard the same thing (radio off again).

Could I have a bad ground connection? Other ideas? Could I be frying anything (DME, other) if there is a problem but it otherwise seems to be running well? I am a bit nervous about driving it now...

Ted

[dshepp806]

How are you monitoring the voltage? Have you a dash voltmeter or another device installed? If so, did you see any spikes on the meter?

Also, was the regulator changed also?

Best,

[tedder]

I was holding my digital multi-meter against the battery posts while my wife was in the drivers seat modulating the throttle.

According to the rebuilder, the brushes are attached to the voltage regulator and these were changed along with the bearings. I wonder if I should rig some long wires to my multimeter so that I can check the voltage while driving...

[dshepp806]

Plenty fine for static, in the driveway checks. I'd suggest positioning yourself with the ability monitor voltage from within the cabin, via a digital guage that will mount into the cig lighter or otherwise (dash mounts, etc.) This, of course, is for the long term and quite a valuable monitor for the car's well-being......don't know why they didn't place a voltmeter in these cars.

Have you a radar detector? I stumbled upon my Passport's ability to render DC voltage readings on it's display, eliminating the additional DC port for my digital. It was the Passport that alerted me to an overvoltage condition!! It stays in the voltage monitor setting. I had visions of an overvoltaged DME and freaked out at the worst case condition......

For what it's worth, I've an extra DC voltmeter guage that will plug in to the cig lighter port and will be glad to send it to you for use....just say the word and I'll have it in your lap in short order....checking to see if you're getting overvoltage conditions WHILE DRIVING.

Yes,..you could rig some wiring from the battery to the cockpit but be damned careful in doing so......

(again) was the voltage regulator changed out?


SO: the radio is turned off yet you hear spurious noises coming from the speakers (intermittently)? Appearing primarily on exit ramps (deceleration)? No other situations?


Best,

[tedder]

The voltage regulator was changed out.

So far I have heard the noise 3 times. Once accelerating (normally) up an on-ramp. Twice decelerating (normally) down an off-ramp. Each of these was with the radio off. With the radio on very quietly I have gone up and down 3 more ramps with no sound.

Where did you buy the lighter-port DC voltmeter guage? I checked our host, Sears and auto-zone and they don't seem to have them so maybe I'll take you up on your offer for your spare as I don't have a radar detector.

[dshepp806]

PM me with your address,..I'll be glad to get it out to you.

I don't recall where I got it....I'll have to check.

Best,

[crashmy911]

911's don't like radios!!!!!!!!!!!

[tedder]

Strangely, my 911 wants me to keep the radio on. Its only when I turn it off that it makes the funny noise. I have noticed though that the last time it happened, the radio was not in fact off, but set to CD (short push of button, changes radio to cd, long push turns it off) and there was no CD in the slot. COuld be that it is just a bad connection in the radio

[dshepp806]

I Pm'd you with a note that I'll be sending out the meter to you tomorrow...

Tell me about the stereo system presently installed in the car.....have you a power amp located somewhere? There has to be something at some voltage potential to get the speakers to emit the sound....

On OFF Switch ok on stereo unit? All wiring checked? Was the battery disconnected for the alt/reg R/R?

Best,

[dshepp806]

tedder,

The meter shipped out today...you should have it early next week.

Good luck and keep us posted!

My best,

[dshepp806]

Any updates as to stereo system anomolies? Howabout answers to the previously posed questions re: stereo config...amps?,..etc...??

Curious as to whatzup?

Le'remedy?

Best,

[tedder]

update: Drove in this morning and used the cigarette lighter voltage meter. The meter was a bit loose in the lighter socket and voltages varied a bit if it wiggled. Voltages were also slightly lower (~.3-.5v) than what I measured at equivalent RPMs at the battery with my digital voltmeter. Something definitely happens as I come off the highway;

Street to highway 2-3k rpm: 13.2-13.7 v
Highway cruising ~3k rpm: 13.2-13.9 v
Clutch in coast down off ramp: 12.6 v for about 2 s then back to 13.4-13.6v

There was a definite voltage drop as I came off the highway. Didn't ever seem to happen when I was clutching and stopping at a light at slower speeds. This was all with headlights on and radio on low.

The stereo is a Nakamichi CD player the PO installed in 2001. AFAIK there is no extra power amplifier mentioned in the maintenance log or that I have found.

The battery cables were disconnected before the alternator was removed.

Next step will be to pull the radio and check the connections on the back. Not sure why there does seem to be a voltage drop on the off ramp though. I can't think of anything that would load electrically differently at speed than when I am coming to a stop

[bigchillcar]

since there is no other power amp drawing from your electrical system, i'm wondering about the condition of your battery? i change mine every 2-3 years (cheap insurance). bad cells can cause odd quirks.

[tedder]

the battery is only 2 years old. It did get run down to completely dead when the alternator went though. Since it seemed to be able to hold 13.4 volts when charged fully I thought it was OK, but maybe only 13.4 in the garage with the car off and not on the road when the revs drop...

[dshepp806]

Has the battery been load tested?

You did mentione that the reg was changed out with the alt rebuild,..which surely would of covered the diode bridge, right? I sure hope your alt/reg is ok,....have you a battery to swap out just to see how the meter reacts?

Mine has no such fluctuations that you speak of,..she stays relatively rock steady..unloaded @ 14.2 - 14.3 VDC....thereabouts.

You can retension the male side/meter's connector to better grip your car's socket. Doublecheck your cig lighter output voltage with the SAME meter you're using for the battery measurement to correlate the two,..THEN check against the meter I sent you.....all, just as reference (accuracy).

Has the stereo been acting up still?

Best,