This story got way too long so here’s the short version.

Just purchased a 2008 Cayman S Tiptronic with 71K miles. Dash went black and loss of all power while on the highway going 80 miles an hour. Had to be towed and the mechanic said the alternator was good and the battery was bad. Replaced battery and all good. Drove it from ATL to Florida with no issues. Once off the highway I pulled away from a light aggressively and the same thing happened, but only for about 10 seconds and then it came back on while driving. I still had about 10 miles to get home and it didn’t happen again, but I noticed the headlights dimmed multiple times while driving.

I’m thinking bad alternator or maybe just a bad connection.

Here’s the long version if interested.

Just got Porsche #4 last Friday. First was the infamous 2011 Cayman S with 160k miles, then the 2007 Boxster S with a flood title and my current 2002 911 C4 (beautiful but the most costly and problematic car I’ve ever owned in the last 30 years and approximately 100 cars). And now my latest purchase, a 2008 Cayman S with tiptronic and 71k miles. Drove up from Ocala, Fl to Atlanta Friday to purchase from Hennessy Lexus. Patrick and everyone there was amazing.

I picked up the Cayman Friday afternoon and drove it all over Atlanta and again until 1pm Saturday with the only issue being that the driver’s side windshield wiper wouldn’t stay in place. Now it’s time to drive back to Florida. I’m on 85 for 5 minutes in the far left lane accelerating up to 80, hit a minor rough spot in the road and everything goes black and no power. So now I have to cross 5 lanes of busy ATL traffic to get in the breakdown lane so I don’t end up dead in the middle of 85. Luckily I made it. I called Patrick and asked if he could recommend a tow service and can I have it towed there and he gave me a number and said to bring it. After 2 hours sitting on 85 the tow truck got there and we towed it to the dealership. With no obligation to do so they paid the $135 tow bill and even though the service department had closed, they kept a mechanic there to look it over. It started right up with a jump and he checked the battery and the alternator. He said alternator was good and the battery was bad. Again they didn’t have to but they put a new battery in at no charge. I’ve never seen anything like it and I can’t say enough about how amazingly they took care of me. I wish the story ended there with me and the Cayman living and driving happily ever after.

But here’s the rest.

I drove from ATL to Florida with no issues. But once off the highway I pulled away from a light aggressively and the same thing happened but only for about 10 seconds and then it came back on while driving. I still had about 10 miles to get home and it didn’t happen again, but I noticed the headlights dimmed multiple times while driving.

I’m thinking bad alternator, maybe just bad connection.

 

 

 

This type of thing can be a nightmare to diagnose.
Get a fault code readout as it might give you a clue.
I would check for a bad ground connection, especially if some major (engine/gearbox out ) work was done on the car.
Mechanics sometimes forget to properly tighten ground connections.
Alternator failure would normally give you warning light and not the full blackout you experienced.
As it seems to be a complete electrical failure, it would indicate that its one of the primary electrical circuits. So most likely somewhere between the battery and the fuse box. Check all the main ground points, but start with the battery ground strap at the point where it attaches to the body, and also check the engine ground strap.

 

Now it appears it only happens when accelerating rapidly. Had it checked out by a competent indy and no loose grounds. There's lots of communication errors in the CAN network, but that's to be expected when you lose all power. No other codes. I've been driving it quite a bit and whether around town or 80 on the highway there's no issues, smooth roads, bumpy roads, no problems. But hit it hard from 50 to 90 and lights out for 10 seconds and then dash lights come on and then engine starts from rolling. When it happens and comes back on the gas gauge is on dead empty and won't return to normal until you put some gas in. Trying to avoid the dealer's $180 an hour. There's a Porsche expert near Gainesville I'm trying to get a number for.

 

PM me the full fault code print out if possible.