Quote:
Originally Posted by wilsonlaidlaw
My car was originally a 1977 911S not an SC, albeit I am now running gas flowed Motronic fuel injection on a big bore block but with 3.3 Turbo crankshaft. I wonder if that makes a difference? Is the diode inside the standard red 5 pin relay or external? The black relay from the horn circuit, which is I believe a simple make and break relay not a changeover, works OK (at least in the short term) on my car in the fuel injection relay socket.
Wilson
|
The diode is internal to the relay. If you look at the wiring diagram for the SC, it includes as over-rev protection circuit (rpm limiter). It is one of 3 things that can put a ground on pin 85 (the other 2 being an alarm system, if installed, and the air pressure plate sensor at the engine). When the rpm limit is tripped it puts a ground on pin 85, which effectively shuts off power to the fuel pump.
I believe the purpose of the diode is to act as a "flyback diode". It is the presence of this diode that makes the red relay different from the black ones. Porsche engineers believed it needed to be there. I would not omit it.