jury_ca

When I purchased my 996TT, the dealer PPI suggested that the alternator was bad since the voltage reading was low (still above 12V). I replaced the battery (with a VARTA) and a rebuilt Bosch alternator from Pelican, which helped somewhat, but the voltage reading ranges from 12.2V to 13.5V with an average reading of 12.8V. I'm also getting terrible fuel economy and I'm thinking the alternator is putting a strain on the motor. The electrical system in the car is stock with no aftermarket equipment.

Searching the forums, it appears that replacing the battery cables seem to be the next step. My car is an '03 located in a very humid environment, and the terminals seem to be oxidized. On the Pelican site, the positive and negative terminals are listed for sale, but most people have found the problem to be the connection between the alternator and the starter motor. Should I replace all 3 of these cables?

One event that occurred shortly after I replaced the battery was a failed fuel pump. Attempts to start the vehicle and not driving the vehicle for 2 weeks subsequently caused the battery to run flat. However, I do not believe that the issue is with the battery.

Macster

Well, I'm not a real sharp battery/starter guy but if you suspect the battery connections/cabling you're at the car so I'd go with that.

Give the cables a good check looking for signs of overheated insulation, cable strands broken.

If you're careful, start the engine then shut off the engine and very very carefully check all battery cables and connections for any signs of excessive heat. Be very careful. I've seen bad cabling glow red from the current resistance. Wrap you fingers around a still very hot battery cable and you'll carry the memory the rest of your days.

And watch out you don't touch the battery connection and ground a ring on your finger or a metal watch band to the car. A ring can melt from the heat before you can get your hand out of the tight spot and scream.

The above is why I stay the heck away from 12V batteries and their cabling.

Anyhow, I meant to check my Turbo's alternator voltage gage a few times over the weekend to be able to report what's 'normal' at least with my car.

The voltage level displayed varies some at some times reading lower than I would think. So much so that when I was on a road trip a while back I got a call from my service manager letting me know my other Porsche was repaired and when did I want to pick it up? I told him it would have to wait until I got back and I asked him about the voltage reading.

I hadn't been paying attention at all for a long time then I started paying attention. Funny how the further one gets from home in his car how things that otherwise don't intrude suddently look serious.

Anyway, the service manager fetched a senior tech to the phone and I spoke him and covered the situation. He listened and said the voltage level can vary.

If the battery is charged up the alternator's output can drop some. Under 13 volts. After starting, or upon turning on the A/C the voltage reading will be higher, over 13 volts.

Might mention though even though you do not think the issue is with the battery, these batteries do not like to be deep discharged.

The battery could have suffered some degradation and well, the battery could very well be the issue.

Also, a battery can go weak or even flat out bad at anytime. A new battery is not immune from an early/premature death.

So, I'd advise you to have the battery checked under load early in the day, then again later in the day to see if just sitting around has the battery going low.

Sincerely,

Macster.

Kevinmacd

Why not take the voltage reading back at the alternator, just to verify the alternator is puttng out what it needs to. Too many times I have been stung by rebuilt alternators. My voltages everythime I check it is around 13.8 goes higher than that on occasion. Thats with all electrical accessorioes on and the AC running. Your symptoms sound like a bad diode in the bridge rectifier, located in the voltage regulator. One other thing check your grounds.

jury_ca

That's what confuses me about this is that I replaced the alternator with a rebuilt alternator which came with another voltage regulator. I'm thinking I should just replace the voltage regulator again since the part cost is under $50 at Pelican. P/N 000-043-206-37.

There was another forum member who had similar symptoms and the issue seemed to be with his wiring from the alternator to the starter, so I'll replace that as well since the alternator has to come out.

Here is a picture of my voltage at startup (mimimum accessories on):



And after driving for 30 mins or so. It drops at least a volt if the a/c is switched on.



Uploaded with ImageShack.us

R5 Turbo 2

90% chance it is your voltage regulator. Replaced mine and all is good.

Be careful that you route the hot lead from the battery the same way on the back of the alternator. There is a "V" channel molded into the plastic. It looks like it can go either way. I did it wrong the first time and grounded the head of the bolt onto another bolt. Big sparks.

jury_ca

Update:

I replaced the voltage regulator on my alternator. Didn't make any difference. I asked my Indie to replace the positive cable between the alternator/starter but he said to try changing the voltage regulator first since it's a lot of labor, and requires a drop of the motor to change the harness.

I tested the voltage at the battery and it is 12.1V when the car is not running, 13.5 volts with the car running and minor electrical load, and 12V with the a/c, all headlights/foglights and the rear defroster running. Voltage will usually drop by about 1v after about 30 mins of driving, but has never gone below 12v.

What's the best way of checking if the wiring harness from the alternator is bad? Testing the voltage output at the alternator vs. at the battery? Where is the best place to connect the positive terminal of a volt meter in the engine compartment? The alternator seems pretty inaccessible.

Ben_C

I'm not really clear what you are chasing - is your battery going flat? Or just the voltage reading that concerns you? The fuel economy issue in your early post sounds like a tenuous link to the charging circuit.

Cheers, Ben

Kevinmacd

To diagnose, take some heavy wire and connect to the ground side of the battery to the car frame. Make sure it's not an area that is painted. Then start it up and turn everything on and see if it imprves. If it does you have a bad ground connection. Just a thought

Sometimes connections get corroded and become heating elements, which will put a load on the alternator and not allow for the battery to see a proper charge. So if the ground wire doesn't help, you probably need to trace the cables and their associated connections.

Macster

Well, one way is to touch the cable. Generally a bad cable will be hot (warm or warmer than it should be) due to increased electrical resistance from a compromised cable or one or both of its connections.

Be careful. The cable can be darn hot. I've seen bad battery cables, ground straps with just a few copper strands remaining glow red hot from the electrical resistance heating when the starter's cranking.

Besides hot there are other serious risks. The cable is probably hard to reach, in amongst spinning pulleys, a serpentine belt, hot exhausts, and capable of delivering considerable amps if one touches it wrong.

Sincerely,

Macster.

jury_ca

The battery is not going flat. I'm just concerned that I can't charge over 13V when the A/C and headlights are on. A year and a half ago, I replaced the battery and the original alternator with a rebuilt unit. Three months ago, based on advice in this forum and eliminating possible issues, I replaced the voltage regulator once again. Hasn't made a difference. The battery has gone flat 3 times from lack of use rather than a fault with the charging system, so it's possible I have an iffy battery. My voltage meter confirms the dash reading, so it is not a gauge issue. Final hypothesis is that it is a wiring / connection issue.

SSST

So everything is working right but you think you have a problem and are trying to fix it? Are you sure you actually have a problem? I just checked and when I have everything turned on, my voltage is just a hair above 12.

I may be wrong, but just enjoy the car, keep up with the maintenance, buy a trickle charger, and quit obsessing over potential problems. When you have a real problem you will know it.

jury_ca

^^Maybe you're right, and I'm obsessing about a non-issue. It's just that when I purchased the vehicle and had the Porsche dealer perform a PPI, they said the voltage gauge was reading low likely due to a failing alternator. I replaced the alternator but it made no difference.

I just checked the voltage drop between the alternator (measured between the positive terminal in the engine bay and ground) and at the battery. There's about a 0.4V drop, which I gather is normal. I followed Macster's advice and felt the battery cable (3 mins running on a cold engine). Battery cables and terminals are cool to the touch. The (+) brass bolt in the engine compartment, however, gets extremely hot and I can't hold my finger on it longer than a couple of seconds. The two steel bolts that fasten the terminal, however remain warm to the touch. I assume the difference in temp is the difference between the steel bolts being warmed by the heat of the engine, vs. electrical resistance generating heat in the brass bolt. (pic below) If this is normal, then I'm going to follow SSST's advice and file it is as a non-issue.

Macster

Based on what I have observed with my 03 Turbo that's about right. With no additional parasitic electrical loads after cold start the volt meter indicates nearly 14V.

After some time the level drops a bit to maybe 13.5V. When I turn on the lights, or the A/C, or both the level drops again to nearly 13V.

In fact I was in Elko NV when I got a call from my Porsche service manager telling me my other car was ready to pick up. I told him I'd pick up the car a week or so later when I returned to the area.

But I asked him about the voltage level -- I had just noticed it was 'low' having turned on the A/C and the lights when I pulled over to take the phone call -- and he got one of the senior techs on the line and he told me that the reading was within the normal range. If there was a problem the voltage reading would be lower, around 12V because the battery would be supplying all power required by the engine.

Without lights, A/C or other any parasitic electrical loads the battery can keep the engine running a while.. hour maybe. (I remember when my VW Golf TDi lost its v-belt and as a result lost power steering and brakes and alternator power (but not the water pump) I continued to drive the car over 20 miles at highway speeds before I was able to get it to a VW dealer for attention. Save for nearly breaking my arms when I went to make a sharp turn (no power steering) the car exhibited no other signs of trouble, other than the alternator/battery voltage warning light came on.)

Anyhow, the missing voltage (the difference between what the gage read before I turned on the electrical loads and after) was going to supplying the electrical loads, not charging the battery. The battery was receiving just enough voltage to keep it charged while the rest was going to power the car's electrical system.

While I can't be sure, I think based on what you've reported there's nothing wrong with your car and its electrical system.

Sincerely,

Macster.

Ben_C

If it were my car I'd disconnect that terminal, give it a clean as well as the inside of the connector to ensure no corrosion and reinstall, possibly with some contact grease (proper name anyone?). Then cease to worry until an actual problem surfaces!

Cheers, Ben

Kevinmacd

My voltage never drops to 12 v . 12V is not enough to charge a battery. Does voltage drop after it hits 14Volt, yes but to about 13.8v. Have never seen it go to 12v. I have to disagree on the feel test. If the cable is very coroded I buy the feel test, but a slightly corroded cable may not demonstrate a noticeable amount of heat yet still cause a voltage drop. I still think you need to check your grounds!