voltage testing
Pro
Joined: Oct 2005
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From: Summerville SC
If you have a hand held multimeter you should check the voltage at the battery with the car running and compare it to the gauge. If it does not agree then you should go to the engine bay and check it at the cable post. If this is okay then you should look at your instruments.
Electron Wrangler
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From: Phoenix AZ
Get a cheap multimeter (do it fast - if you are really @ 16V you are close to frying things....) Radio shack or similar hasd cheap ones - for $20 you can get a reasonable basic version - for $50 you can get a very nice one. Repairing or replacing your cars brains will cost >>10X that. If its real get the alternator fixed - don't drive it....
Alan
Alan
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Racer
Joined: Aug 2005
Posts: 480
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From: wisconsin
Yeah, it real! My voltage @ the battery was around 15.75 and 16.02 @ the front post. Time to get an alternator (voltage regulatorinternal?). Could this be one of the culperates of my emission failure(cold start/afm,etc)?
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Racer
Joined: Aug 2005
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From: wisconsin
O.K., I finally got my 928 running after my tune up. I have replaced the alternator with a rebuilt bosch unit from paragon. I had the battery charged, all connections clean,etc and now the car starts with no symtoms of low voltage, but now I am under 12V!!! The guage in the car is below 12V, The battery while running is 12.1V and the post at the front of the car is around 11.8V!! While the car is running voltage drops slightly and no matter what rpm the voltage idles around the same. The car will repeatedly start with no hesitation, draw,etc. Do I have a bad voltage regulator( new one on new alternator), ground problem?
Electron Wrangler
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From: Phoenix AZ
Umm!
I'd suspect you had damaged the battery by overcharging it - may still be worth checking it out - but that wouldn't explain the battery terminal voltage being higher than the engine jump post...?
Are you sure your multimeter is accurate? Can you try it on another car? (doesn't have to be a 928),
try some differemt ground points for your multimeter in the engine bay... how does your dashboard voltmeter compare now...?
Based on what you say the reading are - you should be discharging your battery... how long have these conditions existed? you say it continues to restart no problem - this suggests it was either very well charged to start with (and will eventually fail) or is getting recharged quite OK....
Something funky is going on here...
Alan
I'd suspect you had damaged the battery by overcharging it - may still be worth checking it out - but that wouldn't explain the battery terminal voltage being higher than the engine jump post...?
Are you sure your multimeter is accurate? Can you try it on another car? (doesn't have to be a 928),
try some differemt ground points for your multimeter in the engine bay... how does your dashboard voltmeter compare now...?
Based on what you say the reading are - you should be discharging your battery... how long have these conditions existed? you say it continues to restart no problem - this suggests it was either very well charged to start with (and will eventually fail) or is getting recharged quite OK....
Something funky is going on here...
Alan
Racer
Joined: Jul 2004
Posts: 475
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From: Princeton, NJ, USA
If the voltage on the battery is higher then on the wires which come out from it, there is a problem in connection between wires and battery terminals. Take the battery cables off, and clean them. Make sure that the inside of the cable clamp is smooth, and doesn't have bumps or holes in it. If it does, sand it till you get a smooth surface. Should work...
Klim
Klim
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Racer
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From: wisconsin
It is funky! The multimeter has been checked against my other vehicles, o.k.. The voltage on the dash while running is around 11 volts, no light comes on, the battery was charged up on a 2 amp charger, and while running the battery shoes 12.35 and the engine compartment post shows 12.04, is the new alternator and/or regulator need to be looked at?
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Nordschleife Master
Joined: Jul 2003
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From: Minneapolis
There's something wrong, that's for sure.
Is the voltage higher when running than off? That's say that it's doing something. Otherwise the alt is bad, usually the regulator, or it's not hooked up right.
Is the voltage higher when running than off? That's say that it's doing something. Otherwise the alt is bad, usually the regulator, or it's not hooked up right.
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Joined: Jan 2004
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From: Boulder Creek, CA
If you're not getting ~14v at say 2500RPM then your alternator is not doing its job. Check all connections -- grounds, Alt output, jump post, battery cables. See if the cables are real stiff near the battery terminals, indicating creeping crud(corrosion) moving up the wire under the insulation.
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Racer
Joined: Aug 2005
Posts: 480
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From: wisconsin
FYI, the reason I am replacing the alternator and the regulator was that the car was running 15.5 to 15.75 on my way home(45 miles). I thought since I was underneath and did not know the history/age of the alt., I felt I should replace both as one unit. Now I get the rebuilt unit, hook it up the same, and have a low voltage problem! I have tested @ the alternator, battery, post and the voltage output is similar, right around 12 volts....
Thread Starter
Racer
Joined: Aug 2005
Posts: 480
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From: wisconsin
O.K., the problem is the regulator, I did some part swapping. The old alternator w/ the new regulator will not put out over 12V, the old regulator climbs fast to 15V. Shut it down and get the new alternator/regulator exchanged for another unit...
