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Sebastian Vizcarra
Sebastian Vizcarra, Porsche Meister Tech
Category: Porsche
Satisfied Customers: 350
Experience:  Porsche Factory Certified Master Technician
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I have a 1978 porsche 911. The fuel pump used to come on when

Customer Question

I have a 1978 porsche 911. The fuel pump used to come on when I turned the ignition on. It no longer does so. However if I crank the engine 3 seconds or more the car starts and runs fine. Intermittently the fuel pump does come on with ignition on
JA: Thanks. Can you give me any more details about your issue?
Customer: I have changed relays several time and same result as above
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Submitted: 1 year ago.
Category: Porsche
Expert:  porscheguru replied 1 year ago.
The fuel pump is protected by a safety switch on the fuel distributor air meter flap. It is intended to protect against a fire in case of an accident. If the engine stalled but the fuel pump continued to run after an accident, the results could be deadly. So they integrated this switch so whenever the flap moved (engine cranking allowing air into the engine) the fuel pum would activate. But alot of mechanics would unplug this during fuel system diagnosis and either leave it disconnected or just forget to reconnect it. Either the switch is failing (it is in the back and hard to see) or you recently had service work done and the mechanic reconnected it. But since you say it is intermittent, I suspect the switch is the culprit. Let me see if I can get the part number for you.
Expert:  porscheguru replied 1 year ago.
Here is the part number but my pricing did not show me anything for this. I is item #6. I think you might have to lower the rear of the engine carefully to gain proper access. Take a peek at yours.