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"Pump-Prime" relay from ftech9
The Pump-Prime feature automatically runs the fuel pump for up to 3 seconds when the ignition is switched to the "On" position. This builds optimum fuel pressure before cranking the engine, insuring your Porsche starts as fast and as smooth as it possibly can. You can hear the pump run before cranking the engine; perform a self-test every time you start the car. The standard ftech9 relay works just like the original relay--it doesn't turn the fuel pump on until the engine is being cranked over by the starter.
993s have pump prime already built in from factory I believe. This feature is for 964s.
Some further clarification on exactly how the original DME relay works. The fuel pump relay is incorporated into the DME relay. The engine has to be cranking at minimum 30 RPM before the fuel pump will energize, so no pre-prime, nor do I find it possible to hear when the pump starts using an original relay. This is from the Bentley shop manual:
No rhyme or reason, they can go bad at any point. Just always have a spare on hand.
Definitely good advice. My car had 73K miles when I bought it and that DME failed at around 75K, Unfortunately while I was actually on the road driving the car. Fortunately, I had a spare. No idea what I'd have done without one.
FWIW, that was about 2 years and 5K miles ago and no repeat failures so far.
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