Porsche 911 3,2 loosing power intermittently....

jsoderbe · 07-28-2010, 09:04 AM

Hi,

My 3,2 Carrera Convertible has been a perfect driver during this very nice swedish summer. There is only one thing that I find very strange; it looses power sometimes! Not all power, but it feels like it looses maybe 10-15 hp at full throttle.

The really strange thing is that it doesn't come and go while driving, it's different between the different times I drive it. For example, today I drove 100 miles before lunch, and had full power. After lunch I drove back, and it felt slower.

It runs exactly the same, no smoking while power loss, no noises, nothing. The only thing I can think of is that the engine sound is different when at full throttle, it sounds more powerful. Strange.

It doesn't matter if the engine is cold or warm, or if I fill it up with premium or better gas. Doesn't matter how many people in the car, or how fast I am driving.

Can my feeling be wrong? Can it be the difference in outside temperature, moisture or something like that? Today the difference was maybe 8 degrees fahrenheit between am and pm.

I know that it need a valve adjustment, other than that it has new oil and new spark plugs. It has a pretty high CO, around 3,5 %, for a Motronic system. Can I have a faulty sensor, or something like that? How do I check when it's intermittent?

Any ideas?

Thanks,

Johan

jsoderbe · 07-28-2010, 09:10 AM

Maybe I should clarify with the fact that it is a US car with cat and all that stuff....

Johan

DW SD · 07-28-2010, 09:24 AM

I'd look at the full throttle switch on the throttle body. If that is intermittently working, it could cause the issue you describe. While you are at it, I'd also check for full throttle from the pedal itself.

Doug

cgarr · cgarr's Garage

As long as your full throttle switch is working that should bypass the sensor in WOT, could be injectors, fuel pressure, air meter box, foot on the brake etc?

jsoderbe · 07-28-2010, 10:17 AM

Ok, thanks. A full throttle switch, that was news to me....

I'll start with trying to find that one. Thinking of it, the pedal assembly does feel a bit strange, the accelerator pedal almost feel like it get stuck sometimes. Could anything be wrong there?

Thanks,

Johan

stlrj · 07-28-2010, 02:16 PM

3.5%? Seems a bit rich for Motronic.

rusnak · 07-28-2010, 02:49 PM

You could have a bad O2 sensor. It makes sense to me to check your fuel pressure, and the CHT sensor, as well as adjustment of the WOT and throttle linkage. You can't know until you go through the process of inspecting the system.

Do you know what the lambda ratio is of your system? Make sure the vacuum line is connected to the fuel pressure regulator.

stlrj · 07-28-2010, 03:02 PM

Quote:

Originally Posted by jsoderbe

It has a pretty high CO, around 3,5 %, for a Motronic system. Can I have a faulty sensor, or something like that? How do I check when it's intermittent?Any ideas?

It could be a bad cylinder head temp sensor, CHT.

rcaradimos · 07-28-2010, 08:14 PM

Dose humidity affects it? Could be corroded connections in the ignition wires boots. Humidity can set in and it shorts out a cylinder. After a long drive everything can dry out. These cars run well on 5 cylinders. One cylinder out is like a 16% loss in power.