ontario

I have my car back on the road and I'm trying to resolve a problem from last season. I had occasional voltage spikes up to 17 volts. These would occur only when the alternator was under load - when I was revving the engine. Never at idle. Sometimes, the spikes would start right away, as soon as I pulled out of the driveway. Other times, they would start a few miles down the road.

I immediately suspected a bad regulator so I pulled the alternator, had it rebuilt and re-installed it. All seemed well for a few days but, the voltage spikes returned. I put the car away for the winter and resolved to deal with it in the spring.

This spring, I took the car to a mechanic and he and I went through every ground on the car. We noticed the battery ground was bit loose and my mechanic thought that might be the problem. We tightened it up but it didn't help. His conclusion was - bad voltage regulator.

So I pulled the alternator again and took it to the rebuilder. He bench tested it and told me there was nothing wrong with the regulator. To be safe, he is replacing the regulator.

Is there anything else I should look at? The battery is about 3 years old and it's an Optima Red.

Did we catch all the grounding points? There's the battery ground, one under the car in front of the engine and another under a cover on the left side of the engine bay. Any others?

Car is a 1988 911 3.2.

Thanks,

Henry in Ontario

old man neri

How are you measuring these spikes?

ontario

With a multimeter on the battery terminals. I noticed them for the first time last spring when the stereo amp kept cutting out (overload protection). No other symptom. Tach is working fine.

wwest

If it's a digital multimeter it might be an aspect of the voltage sampling circuit of the meter itself. I wouldn't rule out the meter in any case.

17 volt "spikes" across the posts of an already fully charged battery would normally indicate a battery cell going open temporarily. It would take a LOT of inrush current to raise the terminal voltage of a fully charged good battery from the norm of ~13.5 volts to 17 volts so I would be much more likely to suspect a temporary battery high resistance internally.

ontario

I tested myself with my multimeter plus my mechanic tested it. Plus, the stereo amp keeps overloading and shutting down so I'm pretty sure the voltage fluctuations are real. I wish it was my meter.

Are you thinking it's the battery? I'll kick myself if it's the battery. I could've avoided pulling the alternator twice.

Lorenfb

"17 volt "spikes" across the posts of an already fully charged battery would normally indicate a battery cell going open temporarily."

Actually not, a good regulator should maintain the proper voltage irrespective
of the battery cells being "open", e.g. even a disconnected battery. The problem
indicated in this thread is typical of a bad voltage regulator. The 90 amp
alt. in the 3.2 is more than capable of producing 17 volts and can get as
high as 25 volts with a bad internal regulator which can damage electronic
devices, e.g. the DME ECM. Most bad regulators tend to over-charge
intemittently, so an alt. test may indicate a good internal regulator.

theiceman

I agree with Loren , If it is not the regulator I would closely at the wiring to it as the field effect for the alternator to charge apears to tbe the issue. ( contolled by the regulator ) if it is not collapsing the field the voltage will ramp right up .

I would also suggest a voltmeter be mounted in the car, depending on how fast the spikes are of course, but you may see deflection in the needle. Personally i think a volmeter in these cars is a must as overcharging due to bad alternators and regulators is a real possibility.

ontario

Are you suggesting the wiring from the regulator to the alternator or the alternator to the car? Wondering if should swap out all the wiring from the alternator while I have the alternator out. How hard is that?

I already thought of the voltmeter and have been shopping around. But, the ones I have seen are ugly chrome jobs. I also wanted to find one that would record peaks. I heard there's a voltmeter you can plug right into the cigarette lighter. That might be handy.

theiceman

i meant the wiring to the regulator , but you should inspect it all very carefully as with the heat and years this wiring can get brittle and the insulation can break down. I have a small voltage meter tucked away ( more for overcharging than spikes ) but I am very comfortable knowing it is there..

ontario

Went out to the garage to look at the wires and took a quick photo. The one with the white insulation on it was a brown one but the insulation was cracked so I covered it with heat-shrink tubing. It's a short ground wire that goes to the engine block and I'm thinking that might be the culprit. Not sure why I didn't think of it before. It will be very easy to replace.

The other three wires terminate at the alternator but I don't know where the other end goes. If I can replace them all without a lot of drama, I would do it. Anyone replace those before?

I could cut and splice to them but I would not want to solder in that confined space

theiceman

no just replace what you can. I also redid my ground to the engine casing there. Did you check the one from your transmision to the body right underneath the car ?

ontario

Will do. I did look at the one at the transmission when I had the car up on a hoist and it looked fine. Would you use run-of-the-mill aluminium connectors from the hardware store or do I need to find special ones? The ones on the car look like copper. I don't even know where to find those.

theiceman

no i just took them off , cleaned up the connector on a wire wheel . cleaned the area and remounted.

I did mean the ground from the transmision to the body ,,, it is a biggie ..

ontario

Where does that wire connect to the body? I saw where it was connected to the transmission and it was solid but I didn't really see where it was connected to the body. I should check it again.

theiceman

If I remember correctly it fastens to the cross member but that can;t make sense. That is the strp i belive that grounds the engine to the body of the car. I can't thinkthey would be independant . I will check my pics but if anyone know off the top of thier head they can respond.