royce911

Hello Everyone,
My father has a 1972 911 that is having some issues. The car runs great for the first 10 minutes but then looses all power and begins backfiring. If you push in the clutch and feather the gas pedal to get the RPM's back up it kinda clears up for 10-15 seconds but then backfires and loose power again. If the car sits for 1/2hr or so it again runs great for first 10 minutes.

We have been chasing this problem for several months now. We have had the car into a Porsche mechanic and he thought is was fuel. He replaced the fuel pump, removed fuel tank and boiled it so perfectly clean, new filters and blew out the fuel line. Unfortunately all this did nothing to fix this problem. The mechanic is stumped and so am I

Any insight or ideas would greatly be appreciated so we can get this beauty back on the road. The car was in Fort Myers, Florida but currently on an auto transport headed for San Diego, CA

Thanks
Royce

theiceman

Could it be ignition affected by Heat?
Did you try checking spark availability and strength during the time of trouble ?

It certainly does sound like fuel starvation but if you are convinced that's fine time to start looking elsewhere.

r911

it sounds like it runs fine when the engine is cold but not after it warms up for 10 minutes

is that right or are you having the problem after it is warm too?


what fuel system is on the car? is it all stock? is a T, E, or S?

royce911

Thanks guys. Yes fuel was our thought as well but as I posted above we feel we have gone through the fuel system. Sometimes I wonder if maybe to much fuel? Maybe flooding? Maybe vapor lock?

Yes engine runs very strong for first 10 min or so. The engine never fully dies but it has now power, misses and back fires like crazy. If I shut it down and restart it sometimes runs great again for 1-2 minutes then issues again. Need to let the car sit for approx 15-20 min before can drive another 8-10 min again.

Heat definitely seams to be effecting something. It is a 911T 2.4L with mechanical FI.

What else changes as an engine gets warm? Vacuum advance... timing?

Thanks
Royce

Steve Weiner-Rennsport Systems

Did the dealership measure the cold & hot fuel pressure & volume at the FPR on the filter?

Did they check the thermostat on the MFI pump to make sure its working properly?

Did they perform the CMA procedures for the MFI?

Did they check the coil and CD box when the car is misbehaving?