Engine suddenly cuts out while driving and then runs fine?

I was stopped at a light and then made a left turn through the intersection when the engine suddenly cut out, with all the idiot lights lighting up. What?! I coasted safely off to the side of the road, got out and checked for an oil slick, (thankfully none) and when I got back in the car, it started right up again, no problem. I drove straight home with no hick-ups even though I tried a wide range of revs and took sharp corners to try to replicate the event. At home I checked major electrical connections (battery, jumper connection in the engine compartment) and everything was tight. For background, I’ve had the fuel pump replaced twice in the past two years (the replacement died after 12 months, exactly 12 months ago!) so that’s what popped into my mind at first, but this time the car started right away again so it shouldn’t be that. Could it be the ignition switch? It was glitchy a few months back, but I haven’t replaced it yet as it’s been ‘behaving’ and I’m lazy. I checked and no codes. Ideas?

Ignition switch. Replace. Don't get the cheap one, buy the more expensive one ~$30.

If you wiggle the key in the old switch with the engine running, you may be able to replicate the fault. Regardless it is a frequent offender so replace it anyway. This will give you a start: http://www.pelicanparts.com/techarti...ering_Lock.htm

Thanks guys - will install a new one and hopefully that's it. Scary as hell to suddenly lose power and brakes on the road.

Take any extra junk off of the key ring. IE: just have the key and a light fob.

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Just the front door key on the fob, non of this going on in my car ...

My brother's keys

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Wow. He could be a school custodian.

Or a prison warden. No way he is sneaking up on anybody unless they are 1000% deaf. (good advice on no extra crap on the key fob, btw)

Well, I replaced the ignition switch (the $30 one) but that's not it. I went out for a test spin and got about 10 blocks before the engine suddenly cut out again. I tried to start it immediately this time and it sputtered a bit before it started, as if it had a gas problem, and then ran fine. I recently put in a 1/4 tank at a different station from where I normally fill up. Water in the gas? I keep thinking fuel pump but why would it be random?

Does it cut out only when you accelerate/decelerate? Or it cut out even when you're cursing with constant speed? I suspect if it's not water in gas, there's gas pickup problem in the fuel tank. Also, did you scan for any error codes?

Ahsai, both times I was accelerating after a stop at an intersection. And not aggressively.

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Did you scan for any error codes?

Yes both times - nothing.

I think you may need to verify the fuel pressure and flow rate from the fuel rail. Another thing you can try is to remove the fuel pump and check it and all the plumbing inside. Is your current pump a genuine Porsche pump? If it is, I thnk it has 2 yrs warranty. If not, what brand is it?

The fuel pump was replaced by the best indy in town just 12 months ago so I guess it's still on warrantee. I've had two fuel pumps go on this car and both times the car was dead as a doornail, but I guess this could be a different issue with the pump. I'll call the indy and see what he says.

I see. Is it a genuine Porsche pump or aftermarket? Sometime it's not the pump motor itself. It could be the hoses or the internal check valve leaking causing marginal pressure/flow. Our mkII fuel system is returnless so the pressure is regulated within the pump assembly.

I'm guessing it's a genuine Porsche part, knowing the shop. I see what you mean about the reduced flow but wouldn't that cause marginal performance .. ie, bucking or bad throttle response?

You would think so but it seems like a good suspect to start with. No code, e-gas, occurs only when accelerating...seems less likely electrical. I'm not saying it's the fuel pump for sure but based on the symptoms, checkng the fuel flow and pressure sounds logical.

Thanks for your input Ahsai. I tend to agree with you. The best I can do is check for connections etc as I don't have the equipment to check the fuel pressure. I'll see what I can find over the weekend.

Maybe the crankshaft position sensor is crapping out. A cheap and easy fix.

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Mike, that could be a possibility, though the symptoms don't seem similar from what I've read. (That said, I'm open to the fact that my situation could be different.) And no P0336 CPS code. But I will certainly keep it on the short list of possibilities in case the pump thing doesn't pan out.

I agree that it doesn't sound 100% like a CPS, but close enough that I would at least consider it. When my CPS crapped out I had no codes at all. Took awhile to figure out what was wrong. I replaced the fuel pump first, thinking it was going bad.

Interesting! Thanks. Sometimes it's the most unexpected thing. Last year I had a vacuum leak, replaced hoses, etc to no avail. After much scrutiny, I finally found a tiny crack in the bottom of the vacuum reservoir. Two days of head-scratching and a $20 fix.

Thought I'd give an update - I had the fuel pump replaced and that solved it.

Glad you got it sorted and thanks for the update

BTW, do you know why your car is eating a fuel pump every 12 months? Good that Porsche offers 2yr warranty on their parts.

No idea Ahsai. The first, exactly two years ago, was probably just the old original pump on it's last legs. The second, we thought might have been a bad pump off the assembly line, but this third one ... a head-scratcher. The service manager couldn't figure it out either and he’d be the one to see repair patterns with these cars. I normally do my own work but I’m glad I just happened to take it into the shop that first time, considering how it’s evolved.

That's interesting to know. I don't think I've seen any thread of 996 eating a fuel pump every year until now Hope this one will last much longer!

Ditto. It's a PITA!