pp000830

Well it may be silly but getting back to basics, Are you absolutely sure you alternator belt tight? The click belt tension tester comes in two versions with differing ranges. Slipping during running be hard to observe

benjr

I replaced the ground strap and that didnt work, double checked belt.

Ended up pulling the alternator. I was completely shocked to discover the ground wire shorted and burned the insulation off the ground wire. Part of the loom was melted but the batt wire and alternator light wire are fine. I never smelled an electric wire burned smell either.

Question

Does anyone know where the harness from the back of the alternator goes? I found a diagram online that suggests it goes to the starter first. If so can I just replace the harness to the starter? I may be tempted to just splice into the unburnt the section of ground.

Looking at the alternator more closely its evident that the alternator case is cracked. The metal from the case shorted to the capacitor terminal and burned up the ground. The base of the voltage regulator is slightly cracked too. It wasn't this way when I installed it. After thinking about it for a while I remember when i was tightening the fan shroud strap i heard a pop (cracking) sound. The tolerances in the shroud are very tight especially since I had the shroud powder coated. Not only was the alternator so tight in the shroud but the fan was scraping at the bottom. The place supposably had done a lot of these but that seems to be my issue. F$^%$^%$ I wish I wouldn't have powder coated !

At least the alternator is under warranty...


See pics attached

benjr

I replaced the ground strap and that didnt work, double checked belt.

Ended up pulling the alternator. I was completely shocked to discover the ground wire shorted and burned the insulation off the ground wire. Part of the loom was melted but the batt wire and alternator light wire are fine. I never smelled an electric wire burned smell either.

Question

Does anyone know where the harness from the back of the alternator goes? I found a diagram online that suggests it goes to the starter first. If so can I just replace the harness to the starter? I may be tempted to just splice into the unburnt the section of ground.

Looking at the alternator more closely its evident that the alternator case is cracked. The metal from the case shorted to the capacitor terminal and burned up the ground. The base of the voltage regulator is slightly cracked too. It wasn't this way when I installed it. After thinking about it for a while I remember when i was tightening the fan shroud strap i heard a pop (cracking) sound. The tolerances in the shroud are very tight especially since I had the shroud powder coated. Not only was the alternator so tight in the shroud but the fan was scraping at the bottom. The place supposably had done a lot of these but that seems to be my issue. F$^%$^%$ I wish I wouldn't have powder coated !

At least the alternator is under warranty...

pp000830

Just a data point - My 993 draws a little current when the car is off and it sits. If I lock the doors with the fob the draw seems to fall off. I now always lock the doors whe the car sits and have never had a battery issue.

IXLR8

Its all part of the engine harness.


It does. And from the starter, it goes to the battery.


Not the harness itself since it is part of the engine harness.

You might be able to pull a new wire through, but I doubt it due to friction within the harness plastic sheathing.

Do it right, replace the harness.

Are you sure you had the wires connected where they should be connected?

Can you peel back the harness insulation and check what color insulation is on that cable.

EMBPilot

i went through two reman alternators in 48 hours as well due to the learning curve here, you are not alone.

the torque value (im sure you know this) on that strap is very low because any real pressure on it can deform the whole thing. its something like 10nm or less i think...

sucks about the wire loom

IXLR8

As for the Bosch or any other brand remanufactured alternator, you'd be disappointed if you knew how and what they do to them. Bosch lists what they do on their site. No thanks!

User 122821

I went through 2 alternators "rebuit from Bosch" on a friend's 993 before everything was right. First one had a bent shaft. The second didn't put out enough voltage. I learned my lesson. I'm buying it directly from Porsche dealer.

Geez, it's not rocket science to test an alternator before it goes out the door. What's wrong with these businesses.

Falcondrivr

The original alternator that came on the car as delivered is of a much higher quality than a reman unit. I took mine to a local alternator shop and they rebuilt it for less than $150. Brushes, voltage regulator, bearings, the works... The down side is that this takes a few days...

OP: I think maybe your wiring harness wasn't installed correctly after the install of the new one? It's been a while since I had mine out. But it seems like I remember a specific routing of that cable. Sorry it happened to you. That looks like it really sucks.

Vorsicht

Is the wiring harness original or is that the one from the recall. If original you can get it replaced for free at the stealer.

kjr914

A possibility is that the alternator was installed 90degrees off and the wire harness was sitting on the top of the engine and melted. I did this accidentily during an install, but caught the error during re-install, luckily (and then broke the alternator trying to remove it from a newly powder-coated fan shroud, yes will paint it next time. But we won't bring that up....)

Was the gnd wire on the back of the alternator broken and frayed? IF it was, its resistance would have gone up, thus causing a voltage drop and power dissipation, thus heat and could have melted the wire casing. That wire looks strangely discolored, which is why I ask.

benjr

I was thinking of that possibility too. What orientation is correct? My harness was melted but the harness wasn't on the engine. The ground was broken and frayed. What does that mean ?

budge96

I am installing an alternator on a 3.8 Cup motor I'm installing and had a question on the same orientation and have looked at your photo..
There's not much room back there and if the positive cable comes in contact with the alternator shaft you'll get this same burnt resistance in the positive cable.
Your's looks pretty toasted about the same as one I removed from my TT a few years back but that was from years of use and prior to the recall installation..
Your's looks recent...

kjr914

The wire harness leaves the back of the alternator out the right/passenger(US) side. If you put it in with the harness going out the bottom, this is the wrong way. As you slide the whole thing back in, it will be obvious the wires are on the engine block, as you can look down into the cavity where the fan shroud goes (you know, the one that appears in every thread with a title like "Plastic thingie broken" ). Of course figure the direction out BEFORE tightening the @#$% alternator into the fan shroud (BTDT).

As I was suspecting, sounds like your ground got frayed, became higher resistance, then generated lots of heat and caused the wire case to melt. Also, if your voltage regulator died and the voltage was much greater than it should have been, this could have made it worse, increasing the heating in the wire.

IXLR8

That would have acted as an insulator.

The alternator being bolted to the shroud which is then held onto the engine by the retaining strap would/might have lost its "ground" path due to the powder coating and relied on the ground wire in the harness. I suspect Porsche uses a ground wire to make sure they have a good ground instead of relying on the metal to metal contact of the components which if aluminum oxide forms (corrosion) would increase resistance between them.

I don't know how your cable could have frayed since there is no movement to it. It just sits there.

I made up a ground wire for a local 911 owner on his older model which used a separate ground cable. The following thread describes the resistance found...

While you are in there * Alternator Cable