Porsche Enthusiasts Club Forum

Hi everyone.

My last problem took 4 months to solve but finally my car will rev higher than 2500rpm! I got really tired of driving everywhere at 75mph! Now it flies...

My next problem is slightly smaller but just as annoying. My car cuts out in traffic when the engine gets hot enough for the cooling fan to switch itself on. The symptoms are just like it runs out of fuel (revs just die - no response to goosing the throttle). First thing I tried was replacing the fuel pump and filter...no good. I left the pump strapped tight to the body so I can hear it humming - however it starts to go erratic just before it cuts out - and seems to more or less coincide with the fan kicking in - certainly within a couple of minutes.

I'm told that the pump is constant delivery and that it starts to run when an engine sensor tells it the engine is turning over? If thats the case - given my previous problems with engine sensors, this seems the best place to start. Other than that, all I can do is try a new power supply to the pump, but I dont know where to take it from?

There are no problems with the car when is moving at speed (better airflow across the engine I guess meaning the fan never cuts in). The cut out happens at idle or low speed (like pulling away from a junction). I have found I can actually control the problem by keeping the interior heater on all the time (takes heat away from the engine so it never gets hot enough!) As long as the engine temperature in the bottom 1/3 of the gauge - the problem never happens! - But I end up very sweaty on rainy days - not good when I get to work after 2 hours driving..

Has anyone got any ideas?

Sparky

There is a temperature sensor towards the front of the engine hiding under the inlet manifold.
Mine used to cut out in a similar manner.
I thnk the part is about £30.00.

Someone else maay be able to through more light on it

might be the FPR (fuel pressure relief) valve.

Before replacing the fuel pump and fuel filter you should have tested the fuel pressure and the fuel pressure leakdown . There was probably nothing wrong with either your pump or filter.

It costs £10.00 to buy a simple pressure guage and 15 minutes to connect it to your fuel rail with a short bit of garden hose.

Use the search feature on the 944 forum as the fuel pressure ,the fuel flow and the fuel pressure leak down tests have been detailed recently by me.

The erratic noise you hear could be your DME fuel pump relay activating and deactivating which is cutting the power supply to your fuel pump.

The fuel pump pumps for about 1x second when you switch the ignition on. It then turns off. It will start to pump continuously when the ECU receives correct information from the various sensors including the crank sensor etc.

If you fit a 3x way bypass cable in place of your DME relay you'll probably find that the problem will go away completly which will pinpoint the problem is due to DME relay activation

Thanks guys,

On the Temperature sensor from Richard - I cant see that a sensor malfunction would stop the car? I'll try it as he said it fixed his though...

On the DME relay and Fuel Pressure regulator from Peanut - I forgot to mention I got a mechanic to swop out the relay....no difference, also I swapped out the DME with another ..... no difference. Also whilst the fuel pressure does seem to be fluctuating like he says, this doesnt take into account the temperature component (how come it only cuts out when running hot).... I will however buy a gauge like he says... update in about 2 weeks as I'm off on holiday tomorrow. If anyone has any other theories - I'd like to hear them?

Sparky

There are two coolant temperature sensors on a 944 . The radiator sensor controls the electric radiator fans

The coolant temperature sensor Richard mentioned is fitted to the head and tells the ECU what temperature the engine is at so that the ECU can operate your cars cold start mechanism and control fuel delivery. There is a simple test proceedure for the sensor on Clarkes Garage workshop.

The sensor only costs £20 or so and is vital that it works correctly. it would be a good investment to just replace yours.

you must follow a systematic test sequence or you will learn nothing about the problem and quite possibly do more damage.

I suggest you take a break from the problem and come back refreshed. We'll still be here to help you sort the problem when you get back.

FPR would be my guess too. Had to replace mine & failure is quite common. The car often still runs but loses power when they die. I got one from Lindsey racing thats adjustable & comes with a pressure gauge for around £30. Engine ran much smoother after it was fitted. Guessing gets expensive & as Peanut says it's far better to be systematic.

Hi Guys,

Well its sorted....thanks for the help. I bought a FPR from theporscheshop.co.uk for £68 and a coolant sensor for £30 from a local dealer - fitted both at the same time as I had to take the fuel rail off anyway. Started her up and she's burbling nicely.

Thanks a lot for your help.

Sparky

glad to hear thecar is running well again.

Thanks for the feedback which will hopefully be useful to others in the future with a similar problem

Be careful with Porsche shop. Usually cheaper from OPC. Always check the price. Glad you got it sorted.