Strange Low Voltage Problems

[logray]

My car has developed a strange voltage problem I've been chasing for at least a year now.

History of my US 99' 996/C2

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Purchased 2007 w/40k miles

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Starting car: voltage around 12v

Warm up to ~190 degrees: voltage is 14 to 14.5v

After warm up: voltage steady at 13v for hundreds of miles in a single drive (meter at half way point)

Car could sit for 10 days without having to charge.

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Somewhere around winter of 2008 to present and 68k miles

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Starting car: voltage drops as low as 10v

Warm up to ~190 degrees: voltage is 14 to 14.5v

After warm up: voltage is steady at 13v

Sometime later during drive: voltage steadily drops, sometimes as low as 12v (I have a pioneer HU that reads voltage and confirms the dash gauge reading)

If it sits for more than about 7 days sometimes the battery needs to be charged again.

Driving the car every couple days seems to keep enough charge in the battery to avoid the problem above.

I've had a couple times where the battery is completely drained and have had to put it on a charger.

I've also bump started the car a few times when there isn't any one around to jump it. :-)

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Things I've tried so far:

2 new batteries, most recent one about 3 months ago.

Rebuilt alternator.

Replaced starter with new.

The voltage seems to dive to around 12 volts when the radiator fans start after the car is hot, perhaps they are on their way out and are sucking excessive voltage?

Where to go next?

[dr914jr]

I hate to say it but if i were in your shoes I'd replace the alternator again.

[RFM]

I would check the voltage output directly on the rear of the alternator, with a good voltmeter. Check the voltage also on the battery and note the difference between both results, they must been aprox. the same (1 volt difference is too much). Check also the ground between: alternator and engine - engine and car body - car body and battery, resistance in main power cable. These are the most common power load problems if the car is equipped with a GOOD battery, a GOOD alternator and regulator, occasionally the DME can be faulty, he controls the load via the thin blue wire on the alternator but is very rare, i think your US car is not using already this system but you never know. If you cant do it by yourself, bring your car to a car electrical specialist such as a BOSCH center.

[wvicary]

One trick I use to test for a faulty ground is to substitute the ground using a pair of booster cables.

[logray]

Thanks! I'll experiment with some of these measurements.

I have been reading on various forums that sometimes the ground strap cables can be suspect (corroded?) on older cars and are the cause of similar problems, but the cables I have seem to be corrosion free and don't see any rust or breaks - the cables are still pliable and not rigid (at least as much as I can see without cutting off the protective sheath).

Yesterday when I had the mufflers out to do a compression test and replace spark plugs I noticed what looked to be one of these cables near the rear of the engine passenger side, are there more than one of these on the car? Assuming one at the engine to body and another at the battery to the body, I suppose the one I saw could be the cable for the engine to the body, just want to be sure I know what points to test.

Thanks for the tip on the booster cable!

I would hope I ruled out the alternator when I replaced it and it had no affect whatsoever. Unless you are saying the original one was bad, and then I replaced it with another bad one?... I guess it is possible.

Any ideas how to isolate a bad DME if that is the cause?

Edited May 12, 2010 by logray

[grahamtwatson]

I'm in a similar place - very similar readings. In my case I've got 12.4v at the battery engine off, 12.8v engine on. This seems way too low - I believe it should be in the region of 13.8v engine running. Recharging using a battery charger overnight got the voltage up to 12.8v engine off, but after driving in to work today it's again a little lower.

I'm going to take my car down to Schucks tonight (or O'Reilly as they are now). They can test both the battery and the alternator on the car and find many problems.

By the way, I've got one of these - http://www.duracellp...erpack-300.aspx - it's saved me having to bump-start a couple of times.

It must be battery season - I've just replaced the battery on my daughters car, my son has just replaced both battery and alternator on his...

Edited March 2, 2010 by grahamtwatson

[pepper9876]

What do you measure for ignition off current after one hour? Should be 40 to 60ma. -pepper9876

[Loren]

What do you measure for ignition off current after one hour? Should be 40 to 60ma. -pepper9876

About 40-60 ma with an ampmeter in series (between battery and the positive cable)

[logray]

Problem Solved!

I replaced the power cable (#21/22 in the pic below) that goes from the alternator to the starter and then off to the positive terminal in the engine bay. It was badly corroded at the starter.

While I was at it I also replaced the ground stap from engine to body, and the other one from battery to body.

Since I had to take the generator and starter out to get at all the leads, I had them bench tested at the parts store. Both had near perfect readings and got a nifty print out on each to go in the maintenance file. Glad that the recently replaced alternator and starter were not DOA.

I had to charge the several times drained battery overnight (not the first time I've done this), and now it cranks like a jet engine again. I might have to replace the latest battery sooner than the 3 year warranty due to the alternator not doing it's job because of the badly corroded wires.

About $40 worth of new wire from napa saved me a ton vs. the stealer!!!

No more 12volt readings during multiple successive long drive cycles! Even with the high beams, air con, rear fog, xm radio, eq, rear defrost, stereo amp, radar detector, subwoofer, head unit, interior lights, blower at full, heat on, radiator fans on high, I could not stress the alternator below 12.8 volts.

[jcpr996]

Does anyone have the part number for this cable (21/22) I need to change it. For a '99 tip. TIA.

Edited May 11, 2010 by jcpr996

[Loren]

Does anyone have the part number for this cable (21/22) I need to change it. For a '99 tip. TIA.

Are you sure you have that cable? According to the parts list it was only used on X51 cars.

[jcpr996]

That is the problem i've been having. Dealer said the same thing. I have a cable that goes from the alternator to the starter where it is joined to the cable that goes to the jump terminal. It is really corroded at the starter area. Ill take a pic and post it maybe that will help figuiring out how I can order this.

While I was reading the post again saw this picture. This one looks different its joined at the terminal where mine is joined at the starter. Cable 15-24. Will post a picture in a few hours.

[jcpr996]

Here are 2 pics. One of the cable and a close up of where its corroded at the starter.

[Loren]

That is the problem i've been having. Dealer said the same thing. I have a cable that goes from the alternator to the starter where it is joined to the cable that goes to the jump terminal. It is really corroded at the starter area. Ill take a pic and post it maybe that will help figuiring out how I can order this.

While I was reading the post again saw this picture. This one looks different its joined at the terminal where mine is joined at the starter. Cable 15-24. Will post a picture in a few hours.

That looks like a Boxster cable diagram - the Boxster does not have the remote jump terminal.

We are talking about a 1999 Carrera - correct?

[logray]

The pic in jcpr996 's post is the exact part I replaced, and mine is a '99 996, yes. I couldn't find an exact pic of the cable in the parts PDF, I agree the one (15-24) in the diagram does not look exactly the same. It's definatley the cable that goes from the alternator to starter and then off to the remote jump terminal that was corroded on mine (looked exactly like jcpr996's).

I actually opted to go with my own cable setup, instead of buying an overpriced battery cable, and have been very happy so far with consistent voltage!

Edit: 996 607 019 01 is what I came up with from the parts catalog, and the description is correct - also on Pelican it says that this part may fit other 99-05 996's.

"wiring harness with connection point generator starter"

Odd though as Loren points out that it shows this part is only for 02 and on X51 cars.

Edited May 12, 2010 by logray

[Loren]

Here is the page from the May 2010 PET part list.

If you engine serial number fits in the .01 cataegory you might give it a try or if your engine serial number is in the .03 category - try it.

Let us know if what you get fits...

[logray]

I highly recommend sticking with the factory OE cable.

On the other hand if you don't want to pay the $60 some-odd-whatever for the official part and you're doing the work yourself, I made my own cable with some 4 gauge (not the correct gauge, but it works for me), heat shrink tube, ring terminals, and anti-corrosion grease (which seemed absent from the original setup perhaps because of the protective rubber cover that was also half-disintigrated). My harness turned out to be slightly shorter than the OEM - providing .00000001% less resistence and improving power transfer by .00000001% - and I was able to re-use the corrugated inner duct the original cable was housed in. Almost looks OEM.

An interesting note that the guage of the oem wire appears to be "in between" 0/1 gauge and 4 gauge be sure to go with a high quality cable and crimp job if you decide to make your own. Or if you are in the splurging mood and want an upgrade to the factory spec for your 1000 watt stereo system there's always this:

http://www.monsterca...11&section=four

http://www.monsterca...68&section=four

edit: not sure of gauge, but it is bigger than 4.

Edited November 21, 2011 by logray

[jcpr996]

Thanks guys I'll get to work on this and will let you know how it turns out.

[jcpr996]

Ok I replaced the cable problem is still there. The alternator checked ok. Everything in the battery compartment looks good and tight. Where is the engine to ground cable?? Anything else I can check??

[logray]

I would also check/replace the battery condition and battery ground to chassis.

Engine to chassis ground strap is right behind the rear side of the passenger side rear wheel, an 8-10" 2 or 3 gauge black cable. If you have a jumper cable handy, remove this cable and replace with the jumper cable and retest. Or a new battery ground cable from local parts store might cost $5-10 at most (but might not be the right gauge).

edit: gauge is thicker than 4, not sure what size...

Edited November 21, 2011 by logray

[jcpr996]

Will check all of these. Thank you so much logray. Im pretty sure the end of this is coming.

[logray]

Will check all of these. Thank you so much logray. Im pretty sure the end of this is coming.

I'm sure you'll find it if this is what the problem is. There are a lot of components in the electrical system and you can eliminate them one by one, or just go agro like I did and replace everything! Shoot first and ask questions later. :-)

[jcpr996]

Well final news on this was that the alternator was bad and not getting repaired properly. Got a new alternator all is good. Thank you logray and Loren for all your help!!!