Engared

Hi guys,

Have a curious issue and was wondering if I could get some opinions:

I have a 2007 C4S with around 100k kms on it and so far the car has been relatively wonderful. That is until recently when a ton of maintenance issues have cropped up which has severely damaged my bank account. Something not related to maintenance however is this recent lack of power at the top end I have been feeling. I noticed this a few months ago after a bad tank of gas; a minor and random misfire would develop in the low RPMs. I switched to a higher grade of petrol (above the equivalent of US Ron 93) and the problem still remained long after the original bad tank had gone. It was really peculiar. Discussed it with my mech and he told me to report back to him over the following weeks.

Interestingly, during that time, the misfires went away. However, this was replaced by a very flat power curve at higher RPMs. Previously, above 6k RPM, the engine would basically have a glorious second wind as it builds towards red-line. Now however, the revs increase, but I don't feel that much change in power. The accompanying soundtrack etc. are all still there.

Over the weekend, my mech switched out some vacuum lines during my visit and I had hoped that the problem would have been solved. What I did get however was a pleasant surprise, the vacuum line fix gave my low/mid-range torque and power a huge shot in the arm. The car pulls really hard now in the mid range, harder than ever before. Which is really nice. But the lack of top end power still remains. Under hard acceleration, the car rockets forward initially but as the revs climb, the second wind is completely missing. Which is extremely disappointing. I probably will have to dyno the car to confirm my suspicions, but any ideas what the issue could be?

FYI, I also have the weak start when engine is warm issue and the idle is a LITTLE rough. And when I mean little, I mean very little. The engine seems to be running a little rich at low speed and I do smell petrol regularly but the fuel economy seems to be only slightly worse than normal. But as I picked the car up relatively recently, I do not really know what "normal" is yet. Combined MPGs are between 5.2 km/l to around 7.0 km/l. I live in a big city so the majority of my commute is city driving.

I'm suspecting plugs but from combing through the records, they were changed 20k kms ago, along with the coils. So that is unlikely. Interestingly, the previous owners of the car changed the plugs at regular 20k km intervals. Could it be the MAF? Some symptoms are there but...

I'm getting my shocks done very soon as they are gonzo and my clutch seems to be heading for the scrap heap in short order. Hopefully, that's the last of the maintenance issues so I can get started on the fun stuff.

Any help would be greatly appreciated. Thanks!

nwGTS

Have you checked for any codes being thrown? Have you hooked up a diagnostic device while the car is running to record timing, air:fuel, etc.? This is what I'd do first before throwing money at the problem.

DesmoSD

Did your mech check your fuel system since it occurred with the bad gasoline, fuel injector test? Maybe a fuel system cleaner like BG-44K Liqui Moly Jectron would be worth a shot.

https://rennlist.com/forums/991/9748...m-cleaner.html

The sluggish starts could be starter related.

https://rennlist.com/forums/997-foru...arrera-2s.html

Engared

I'll suggest that to him. Thanks.

Engared

I'm not sure if my mech has done that yet. If he has, he has not mentioned it to me. He's a super experienced mechanic here, probably the most experienced in the country. But he's not exactly super open to ideas. I'll confirm next time I see him.

DC911S

Clean the throttle body, and do the TB reset/calibration. The TB gets really dirty on the plenum side. Mine was black due to junk building up. If at that many miles and its never been cleaned, I'm guessing it needs to be done.

Engared

I don't think it has ever been clean. Is the lack of power on the top end a symptom?

A GT3 throttle body is on the list of "fun" things to do.

DesmoSD

Maybe this might be the culprit but keep us posted.

https://www.pcarshops.com/porsche-91...l-pump-failure

Qwksnke

Pretty sure that is only applicable in the 997.2's

Engared

I will.

sandwedge

I just had my high pressure fuel pump fail. Not a complete failure but enough to trigger some of the symptoms you mention. I can't say that what I experienced was identical to what you describe but there are enough similarities where it may be worth taking a look at as a possibility.

aaks38

If you haven't changed your coils and plugs, might be a cheap way to start. The other things to look for are any loose or broken vacuum lines. After that i would think possibly fuel injector, fuel pump. As someone else noted, start off with a OBD2 scan of the eco.

Engared

They just replaced some vacuum lines and it gave me a ton of mid range power and torque. But the top end is still missing. The Variocam does come on and I feel the power come in but the late surge is missing.

Engared

I heard that was a problem mainly with the 997.2s and not so much the .1s. Ill mention it though.

Ben Z

Could be any number of things. Dx check of codes and parameters would be my essential first step. Given the cost of parts/labor on these cars, the shotgun approach is uneconomical.