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Lost, bewildered, confused, frustrated.......Help!!!!


25 Jul 2016
I thought it would be the best move, now that I have exhausted my own database of likely fault/solution scenarios to ask the 911 UK collective brain to help me solve this issue...

Problem is an occasional loss of power under acceleration on my 2006 2.7 987. It can vanish for days on end and then plague the car for days and then vanish again.

So far this is what I have dealt with...

1. Scanned for codes, none shown.

2. No warning lights at any stage.

3. Used injector cleaner.

4. Changed to Esso Synergy Supreme+ fuel.

5. Cleaned throttle body.

6. Replaced MAF.

7. Replaced air filter.

8. Replaced spark plugs.

9. Replaced coil packs.

10. Replaced throttle pedal assembly.

Now I am struggling to think what else it could possibly be and really need your help to solve it.

One thing I feel that might possibly be relevant is that when I remove the fuel filer cap there is a definite 'whoosh' and a definite smell of fuel. I have just ordered a new fuel cap to eliminate that, but it strikes me as odd as my 986 and 996 definitely do not do this when the cap is removed.

Any guidance, thoughts or advice would be greatly appreciated.
This is similar to a problem I once had with a classic car.

The whoosh when you open the fuel cap would suggest the vents are blocked and therefore after a while the tank almost becomes air tight. No air in means the fuel can't flow properly to the engine, resulting in exactly what you've got.

Is the problem worse in hot weather?
I know nothing of Porsches beyond the 80`s SC... With reference to woosh as has been suggested this can be caused by a build up of vacuum if the tank vent is blocked. The fuel pump has the potential to create vacuum over time as it sucks fuel from the tank.

Fuel caps used to have a vent hole in them to prevent this happening though these days I suspect there will be a charcoal or similar filtration system to provide the ventilation for the tank while preventing fumes fouling the atmosphere...?

Using nothing other than logic (?) if you drive till the problem arises, stop, remove and replace the the fuel cap, listen for the woosh, The engine may falter if you have left it running during this process, as there may be other engine management processes in play, with the cap back on and any possible vacuum now depleted, with luck you might have found a possible clue to where your problem lies...?

If by some miracle the above may work I guess you then have to investigate whatever vent/filtration system if fitted to your Porsche :?:

Good luck.. :thumb:
Thanks, both of you for the superfast replies, very 911 :D

It has defeated one main dealer and two specialists so far :sad:

I guess the main problem with diagnosing the issue is
1. that it is intermittent and
2. when it does occur, invariably, it is when trying to 'make progress' out of a junction followed by no instant opportunity to stop and check it out.

That said I think i shall have to now pull over and investigate no matter the traffic or parking issues city driving might bring.
so, apologies in advance if you are held up by some lunatic double parked or likewise :cop:
can you ping me a pm reminding me of this please .. as always i like to investigate things but i am about to log off till tomorrow night ..

I really wish i had more time sometimes but it is what it is .
You don't mention whether your car is a manual or auto, but many years ago my 2005 997 had a similar issue.

I would be at a junction waiting for a gap in the traffic, go for the gap and the car would suddenly lose power. I would have to re-dip the clutch and hit the accelerator to clear it.

That turned out to be a failing clutch pedal switch.

It mainly happened when pulling away from a stop at a junction.

Thought I would mention it - a cheap thing to change!
Clutch pedal switch is a new one on me but if it fixed your issue then i will certainly be taking it onboard for the future .. i also learn by coming here .

lack of fault codes .. that tells us something .. you don't always need a fault code to work out a problem .

We need to look at what the car cant see or monitor ..

You are accelerating .. putting your foot down and the car isn't responding .. at this point the car needs more fuel , more air and a bit of timing adjustment .. no codes ..

The car can't monitor the CPS or the fuel pressure .. CPS .. ok yeah if its dead .. open circuit but a non start is not your issue ..

Fuel pressure may well be ..

the fuel pump .. it ain't new .. it can cause issues at higher revs when there is a large demand for fuel and its an old pump .. there can also be debris in the tank ..

My favourite one was a bit of a latex glove .. previous work and the glove had dissolved as the mechanic was working in the fuel environment of the tank .. a bit of this now and then got sucked up into the filter and blocked it ..

A lack of fuel pressure .

For me .. i would have a dam good look at the fuel pump .. maybe replace it before moving on .. you could rig up a gauge to check fuel pressure but i feel you probably wouldn't catch it on the gauge when it happens .

I also feel at work i would be comfortable just replacing the pump at this point so that i could prove or eliminate the issue .

based on your description anyways :)

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