Porsche Enthusiasts Club Forum

I have one sick Porsche, which has a problem breaking the speed limit, maybe as the previous owner was a victor I should have known!
If I try and go above 80mph ish hard the vehicle violently shudders, if I drive the vehicle carefully I can take it up to around 110mph before the same symptoms appear. I have asked a few wise men who have told me that it sounds like the turbo is over boosting, when asked how to fit the problem, just face with scratching of the head! Therefore asking wise Porsche petrol heads out there, do they know where I should start to solve this problem? Thanks

That does sound a bit like the overboost cutout. If the system detects that you are making too much boost it drastically cuts the fuel and feels like you have stomped on the brakes. The dash gauge is difficult to read because of small graduations but it should not read more than 1.8 (this is 0.8bar of boost).

Do you have any adjustable boost controllers fitted to the car, the most common is a valve by the banjo volt on the black intercooler pipe cming from the turbocharger. If so I should try turning it down a bit. Failing that it could be that your wastegate is stuck shut or maybe also that the air line to the wastegate is broken so it is not recieving the correct pulse to open the wastegate.

Check out the 951 problem solving sections of Clarks Garage website for full details:

http://www.clarks-garage.com/951faq.htm

I would have thought the only reason the you would get over boost is if the wastegate isn't opening. First thing I'd check is all the little vacuum pipes. They become a brittle over time, when I replaced mine I broken quite a few. Other than that the wastegate is stuck shut.

Thanks for the advice, will start looking at this at the weekend, will keep you posted

I'm sure all the above speeds quoted were obtained on a dyno . Otherwise our friendly highway patrolmen may have a colouring in session on your driving licence.

Ben

But of course, officer!

Car has now completed a few trips to Europe, thank goodness for Germany autobahns, shame about the cars performance to date.

Just been sorting a car with the same issue, found the turbo recycling valve has a pipe broken off it, this is the beige valve you can see under the inlet manifold by the banjo bolts with a 2 pin wiring plug on it