beden1

I went on a 300 mile round trip this weekend to attend a high school reunion party. On the way there and while traveling 65 MPH in 6th gear, the RPMs had a drop off and then a quick return to normal - RPMs dropped to around 2,100 from 2,800. This happened a few times until I stopped at a light and the car stalled.

The car started right back up and held normal idle RPMs. This happened a few times during the next 50 miles, and then the car operated normally when I later took a sight seeing drive through the countryside.

Later that night when returning to my hotel, the car started intermittently dropping RPMs when traveling about 45 MPH in 4th and 3rd gear, and then also stalling at the light. The car started right back up and was driving normally for a time until I got to the parking lot and it stalled out while doing about 10 MPH into the lot.

I started my return trip the next day, and all was fine until about 50 miles into the trip and it started doing it again when going 65 MPH in 6th gear. I stopped at a light next to a McDonald's and the car stalled. This time though, it stalled three times after starting it back up. I started it a fourth time and was able to drive to a parking spot when the car stalled and I coasted into the spot.

I tried starting the car 5 times and it quickly died each time after starting. On the 6th attempt, the idle held and I did a few quick high revs to see if I could clear a possible obstruction somewhere in the fuel line. Whatever I did seemed to work, because I did not have any issues during the 90+ miles it took to arrive home.

I was thinking it could have been the fuel pump, except the car didn't buck and I did not have any warning lights up on the dash. That was really my confusion, because there were never any warning lights.

I have a boat with twin outboard motors and I had the same situation with it last year. It turned out to be clogged fuel filters. I wonder if the same thing happened in the Porsche?

I called the dealer and he said that I could have cleared some sort of blockage, but to see if it happens again, and if so, just bring it up to the dealer if they are open to look at it.

Anybody else have a similar issue with their car and know about the cause?

extanker

not a whole lot you can check without it acting up,although lack of a CEL points to fuel. the trick is to get test equipment on it while it is acting up. it is rare that something gets "cleared"

alpine-al

Could be bad gas. Before the problem first occurred, did you fill your gas tank at a station other than where you usually get gas? If so, what brand?

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neanicu

It sounds to me that it's fuel pressure related. The more you raise the RPM,with the increased air going into the engine,the computer adjusts the mixture by adding more fuel. I think the computer was experiencing a LEAN condition dictated by the O2 sensor and was trying to compensate but couldn't get enough fuel. Read your Short and Long fuel trims using a scanner. I think your Long fuel trim is +10 or something like that,but below +15 when I believe a code will be set.
If you put a pressure gauge on that fuel line,as you're raising the RPM by snapping the throttle,you should see the needle holding steady or increasing a bit. In your case it was probably dropping in pressure.
My bet is clogged fuel filter and/or bad gas. Weak fuel pump could be the case as well.

As a side note,I'd also look into a vacuum leak.

I'd recommend using a bottle of fuel system cleaner,fill it up with top tier Premium gas and drive it like you stole it a bit to clean it out.

beden1

My first thought was a load of bad gas. I filled my tank for the first time with Lukoil, as most of the time, I use BP from a local station.

On my return trip, and after the problem appeared to clear, I filled up again with BP as the tank was than at less than 1/4.

beden1

What fuel system cleaner would you recommend? I had asked the dealer if they could check my fuel filter, but he said that he would prefer to see if the problem would reappear first.

In the mean time, I hope when and if it does happen again, that I don't get stranded and need a tow.

neanicu

No affiliation,but some people myself included,had good luck using Chevron Techron. Bear in mind that it is recommended using it right before an oil change because there's a chance some of the chemicals used in the cleaner can make their way into the oil. Don't know how much truth is in that,but it sounds logical so I'd do it that way.

neanicu

As a little joke,it looks you're not driving it hard enough.
Drive it at WOT and most likely it won't happen again.

beden1

You're probaby right. Driving to NJ when the problem started happening, I was taking it easy and shifting aound 4,500 RPMs. After I cleared whatever it was, I started shifting 6,000+ RPMs. Maybe that's why it didn't happen again?

I had traded a Corvette ZO6 for my Porsche. I guess I'm used to shifting in the 4K ranges because I'd be going too fast on public roads if my shift points were higher.

neanicu

My observation was meant to be taken as a joke,but technically at WOT the TPS is at or close to 100% so the O2 sensor goes in Open Loop and the Computer is not adjusting the mixture,which could explain why it ran better then.
Don't worry about it,do a fuel system cleaning,change the oil and see if the problem comes back. If it does,it might come with a code this time and it will require some diagnostic before throwing parts at it...like let's say a fuel filter.

Quadcammer

high pressure fuel pump?

beden1

My car with 2,600 miles on the odometer had to be towed to the dealer. The problem appears to be the HPFP (high pressure fuel pump). Dealer ordered one and it won't be here until Monday.

Hopefully this solves the problem.

beden1

Bingo!

sameerg

Speaking in out of warranty terms, what is the cost to replace a high pressure fuel pump?

beden1

It will be replaced under warranty. I pick my car up on Monday so I'll ask what the cost would have been.