I have a 70 S engine w/ MFI that is hard to start when it is warm and has not been started after 20-30 minutes. It seems like a vapor lock or no ignition. Any ideas?
I have a 70 S engine w/ MFI that is hard to start when it is warm and has not been started after 20-30 minutes. It seems like a vapor lock or no ignition. Any ideas?
Sounds like a bad fuel pump check valve and the system is not maintaining fuel pressure. When the engine is cold, the sensor tells the cold start valve to inject gas into the 6 throttle bodies. When it's warm, it depends on system pressure held in the system to start. Continued cranking on the starter slowly builds pressure back up and it eventually restarts. A leaky injector could cause the same type of problem, but more often it's the fuel pump check valve.
my mfi was tough to start hot, cold or whenever. new injectors and she starts first flip like a ...well....toyota. vertex had them for 60 instead of 90, but look into the check valve first.
72 911t * 74 914 2.0
I have had that problem with mine since day one. Difference is mine cranks hard when cold or after it sits for a couple of hours. The cold start solinoid doesn't get a chance in Floriduh as it rarely gets below 50 degrees. is the check valve in the fuel pump a separate, replacable part or integrated into the pump making complete replacement of the pump the only solution?
Tabs likes photos...so here ya go Tabby.
Some you can replace the check valve alone. It screws into the end of the pump.
Check with a Bosch jobber and see if they list a seperate check valve. I used one from a Audi, but had to do a little creative adapting.
Yes I had heard that the check valve MAY be in the banjo fitting but Porsche says NLA. I will check with the local racers and see if we can come up with an alternative. Thanks Rick!
i can mail you my old injectors and you can play injector roulette.
72 911t * 74 914 2.0
Thanks for your help Rick. That explains why if I run the pump for 2-3 minutes it will eventually start. Performance Products shows a fuel pump check valve for $20.09. I assume it is located somewhere in the manifold portion of the pump.
Jim Plavan
It screws into the end of the pump between it and the fuel outlet line.
Start procedure? I usally turn on the key...listen for the CD box whine, pull up the black knob between the seats, wait 15-20 seconds more, then turn the key. VROOOM!
Paul D. Early S Registry #8 - Cyclops Minister of West Coast Affairs
"Now, to put a water-cooled engine in the rear and to have the radiator in the front, that's not very intelligent." -Ferry Porsche (PANO, Oct. 1973)