Like the title says I've got a bizarre problem and I just can't figure it out. Car is 2000 Porsche 911 C4 with a 4.8, P59 pcm, single wire alternator. Obviously the battery is in the front. Battery grounds to the chassis from stock. Power runs to the back from stock. I think it's 4 gauge wire. Seems to be good quality wire. The stock car never had problems so I figured I'd use it. I have that running to the back of the alternator stud. On that same stud I have it running to my starter. I have 2 grounds from the motor to the chassis. One on each side of the block to their respective side of the chassis. Car starts perfect. When I first got it together it did seem to have a grounding issue as the starter was just clicking. Redid my grounds and added one and everything seemed good to go.

As the title says the alternator is getting hot when it's running. I'm talking nuclear hot. This is all within 1 to 2 minutes of run time. It's also not charging. However when it is colder here, like in the 60's (outside temp) the car does charge, but just for a short time. Voltage drops from 14 to 12 really quick. Seems to stop charging once it gets hot. I have never encountered this before. These are truck alternators and the harness was a truck harness I altered. I've run at least a half dozen single wire setups and never had an issue. I've tried it with 2 alternators so I've ruled out it actually being the alternator. I don't believe it's a ground issue. I've had bad grounds before and poor main power wire and nothing like this has ever happened. The car is ready to bring it up to temp and get the coolant pushed through the system but I can't and don't want to run it long with it acting like this. Any thoughts would be greatly appreciated. I'm seriously stumped.

 

So I'm guessing it's a 2 pin alternator. If so, disconnect the 2 pin connector and see what it does. It should default to 13.7 volts.

If there is some very heavy load on it externally, that load should be getting hot too.

If you disconnect the 12V stud and the alternator still gets hot, then there are problems internally. Most likely bad diodes or a bad regulator.

 

It is a standard 4 pin truck alternator. Actually they both are since I’ve tried this with 2 good alternators. One I literally took out of my other car. Unplugged it outputs nothing just defaults to the battery voltage.
Today’s adventure consisted of trying various grounds and running a cable straight up to the battery from the back. Results are inconclusive. Out of maybe 25 starts and running it for 3 minutes maybe at a time it seems like it charges at random. I honestly can’t figure it out. Maybe there is an option inside the pcm that I haven’t seen but I’ve run a similar setup like this before on a p59 and had no issues. Also thinking the excessive heat could be heat soak from the engine. The whole engine bay was really hot after I brought the car up to temperature. Still looking into other things but as of right now I’m stumped.

 

Did I read correctly, 4ga from front battery to rear engine alt and then cable jumped from alt to starter? If so, not correct. I would use nothing smaller than a 1/0 POS battery cable straight to starter first. Then 4ga jumper wire from starter to alt output post.

You can use https://www.fabhabs.com/dc-cable-sizing-calculator to help see cable requirements based on voltage, current and cable length.

With cables sized and routed correctly, measure current from alt to see what's happening. Shouldn't see much more than 40amps with fuel pump and cooling fans running and battery close to fully charged.

 

Had a similar issue on my swap in my jeep, took the alternator in and it had bad windings, new one works fine...

 

I said I believed it was 4 gauge. Could possibly be 2 but either way not 1/0. As I also said this is a factory setup and is clearly adequate for the needs of the Porsche originally I really don't think this is the issue. In my own experience I see the power to the starter suffer with undersized wire and you can hear it labor to turn over and there is none of that here but I can move it to the starter to eliminate this as a potential cause. I will check my amperage draw which I didn't do yet. I don't know what the factory fuel pump draws so I'll have to look into that as I'm sure it will effect the reading I'm looking for. I'm also going to charge the battery to full because I'm sure it's running low after the 25 starts I had yesterday. Thanks for the help so far I'll report back with more findings.
On a side note this is a low mount alternator setup with a LS3 corvette balancer so it's closer to the block than I've ever run before. Has anyone ever had transfer issues from the block to the alternator in a setup like this? I had a similar setup on my LSA swap but it was a bit farther away from the block so I can't really remember if it got this hot.

 

I've used 2 good alternators. Did the same thing on both. I can grab a 3rd one just to check it out though.

 

Are you sure there's no short someplace in the car? Usually something gets hot when there's a relatively tremendous amt of amperage running through something.

 

I agree and no I don't know if there isn't a short somewhere. Another thing I'll have to look into.

 

Small update,

I'm nearly certain the car has a bad ignition switch. Once it's started with the key it was doing some other crazy things I started noticing. With the alternator completely unhooked it started drawing big power it was running at 10v. NOT good. So key on and jumping the starter wire it worked fine. Battery charging perfect everything working normal. Apparently these 996 cars are known for issues with the ignition switch but I didn't find anyone that had a similar issue even on a stock car. Oh well. All the fun of a swap car! Thanks to everyone that chimed in.

 

SOOOOO.... you ARE putting in a new ignition switch??

 

It's ordered and should be here in a few days. I'd like to retain the functionality of the key starting the car but if I have to put a push button start in I will.