Carpokes Porsche Forum

Hey yall,

I've discovered a new chronicle on my 951. Sudden and absolute power loss! I've done a little research so far but wanted to come here to share my experience with the community and hopefully connect the puzzle together. So far, it seems like the likely culprits are related to fueling or DME. I've had my car for a few months now and I'm slowly catching up on much needed maintenance and repairs. Previous owner had passed before I bought the car so it sat a long time (in great condition at least) so I'm finding age related problems so far.

What my car started doing: this only happened on Sunday, thankfully it was fine during car week but when I went out for coffee I had complete and sudden power loss on the car when leaving the cafe. Still having painful cold starts when the car sits for a while but fires right up afterwards if this sounds related. It was maybe a couple minutes after startup when I started driving away. I put it into second and there was 0 response from the throttle when applying the gas. I tried cranking once I pulled over and it didn't fire up, let it sit for a minute and tried again which resulted in a successful startup.

What is weird is that I was able to drive around normally after this initial incident, even found some friends on the highway and had some fun pulls up to fast speeds with no issue. Later that same day I went out for ice cream and the car died again not 2 minutes away from my house. I figured I would get it started again and then continue for ice cream. Low and behold not another 2 minutes away the car died again. No stuttering, no misfires, just 0 response from throttle until the engine slowed to 0. I tried getting it started and something popped out the exhaust with some smoke coming out. The smell was awful and unfamiliar which threw me off. I can't really describe it, the smoke was white from what I could tell but there wasn't a lot to be able to see for sure. I got it started a couple minutes later, drove around my community before returning home to take my daily for ice cream instead.

There wasn't any sign of leaks underneath the car, so I'm scratching my head at what could cause this. Part of my wants to believe it's fuel related so I have an excuse to replace and upgrade to prepare the car for ~400hp. Any input is appreciated, I will continue researching on forums and on Clark's guides to see what I can do in the meantime.

Cheers

Very hard to diagnose from symptoms alone, as it could be virtually anything. That said, there are some very common no-start, engine-dying, scenarios with these cars. In rough sense of probability:

1. DME relay. These are known to fail. When they do, the motor won't run. Read up on them in this link, including your exact symptoms and how to jumper it to test. https://rennbay.com/DME-Relay-Info.html Next time the car dies, turn the ignition to on, and look to see if the boost gauge moves to about 1 on the dash. If it doesn't, there's a pretty good chance the DME relay is bad.

2. Speed and Reference Sensors. These flywheel sensors supply the heartbeat to the DME. The connectors are known to fray and fail inside their rubber boots. This can also cause your exact symptoms. Next time it won't start, look to see if the tachometer twitches or bounces when you crank it. If there is no movement at all, chances are the these sensor wires are bad.

3. Lots of other things, including cracked solder joints in the DME or KLR; engine wiring harness faults; frayed fuel injector wires similar to the speed and reference sensor wires; faulty ignition switch; faulty alarm; and more...

Tom wrote: Mon Aug 18, 2025 2:13 pm Very hard to diagnose from symptoms alone, as it could be virtually anything. That said, there are some very common no-start, engine-dying, scenarios with these cars. In rough sense of probability:

1. DME relay. These are known to fail. When they do, the motor won't run. Read up on them in this link, including your exact symptoms and how to jumper it to test. https://rennbay.com/DME-Relay-Info.html Next time the car dies, turn the ignition to on, and look to see if the boost gauge moves to about 1 on the dash. If it doesn't, there's a pretty good chance the DME relay is bad.

2. Speed and Reference Sensors. These flywheel sensors supply the heartbeat to the DME. The connectors are known to fray and fail inside their rubber boots. This can also cause your exact symptoms. Next time it won't start, look to see if the tachometer twitches or bounces when you crank it. If there is no movement at all, chances are the these sensor wires are bad.

3. Lots of other things, including cracked solder joints in the DME or KLR; engine wiring harness faults; frayed fuel injector wires similar to the speed and reference sensor wires; faulty ignition switch; faulty alarm; and more...

Thanks for your reply Tom! Luckily my car has the Focus9 DME relay with diagnostics. I’ll try your suggestions when I get home today.

Sounds good. Check for tach bounce. The sensor's are the next most likely thing...

Sounds like a fuel delivery issue possibly the fuel pump, filter, or injectors clogged from sitting. The white smoke and bad smell could be unburned fuel igniting in the exhaust. Check fuel pressure first, then inspect the pump and filter. If it’s old gas, drain and refill. Cold starts struggling points to fuel or possibly a weak DME relay. Start with the basics before diving into upgrades.

Evan wrote: Mon Aug 18, 2025 5:33 pm Sounds like a fuel delivery issue possibly the fuel pump, filter, or injectors clogged from sitting. The white smoke and bad smell could be unburned fuel igniting in the exhaust. Check fuel pressure first, then inspect the pump and filter. If it’s old gas, drain and refill. Cold starts struggling points to fuel or possibly a weak DME relay. Start with the basics before diving into upgrades.

Well I planned to take care of all maintenance and repairs before upgrading. I just plan to upgrade the parts if they are to be replaced is what I meant.

I agree with the unburnt fuel, I was trying to crank so it probably dumped fuel into the hot exhaust.

So this evening I went to start the car and it fired right up without struggle which was odd. It was about 82F out so maybe that I checked battery connections which were solid, found that there was this kink in the temp sensor seen in the photo below. This could be a culprit to cold starts? Regardless, drove 20 miles on a mountain road (quite bad road conditions which could help shake up sensor connections). The car didn’t skip a beat, deepening my confusion.

I don’t see the photo upload so I’ll try again and forgive me if it’s a double post.

That kinked temp sensor hose is a classic vacuum leak. It would absolutely cause cold start problems. The rough road probably jostled a bad electrical connection loose, which then temporarily fixed itself. You found your culprit. Replace that hose.

That was my thought. I was reading up on hard cold starts and this was the easiest part to change out buuuuut I wasn’t expecting this haha.

What I meant on the rough road was that it should’ve had jostled some parts but it drove great with no issue.

If that doesn’t stop it’s misbehaving, cure the DME. Install a solid state F9 unit and be done with it. Whatever’s left over is another issue at hand.

These cars like to be diagnosed systematically.