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John U
07-01-2011, 09:39 AM
Is the fuel pump supposed to prime the system every time the key is turned to "on", or is it a function of something else such as fuel system pressure, temp, etc???

thanks
John

DMCMW Dave
07-01-2011, 09:41 AM
It's a function of the RPM relay. Some do it, some don't. It depends on how it reacts to the initial turn-on. If you "bump" the starter without starting the car it should run a few seconds and shut of in any case.

John U
07-01-2011, 09:56 AM
When I put the VOD back together, it primed when I turned the key. Since then, it seems that it doesn't prime after the car has sat a day, but when I start it, turn it off, then turn the key again it primes....I thought it would be the opposite and prime when the car has sat a long time rather than when there was fuel pressure in the system?

Bitsyncmaster
07-01-2011, 10:20 AM
When I put the VOD back together, it primed when I turned the key. Since then, it seems that it doesn't prime after the car has sat a day, but when I start it, turn it off, then turn the key again it primes....I thought it would be the opposite and prime when the car has sat a long time rather than when there was fuel pressure in the system?

When I first got my car and was running the OEM RPM relay it would prime most of the time. But I found out if I left a battery charger on, it would not prime. So it seemed the OEM design was sensitive to the battery voltage. I don't the the relay is designed to force the prime but turning the key on does energize the ignition ECU and that may fire the RPM relay.

My solid state unit is designed to always prime on power up. Does not need any ignition pulse since the micro-processor performs the priming.

John U
07-01-2011, 10:55 AM
But I found out if I left a battery charger on, it would not prime. So it seemed the OEM design was sensitive to the battery voltage.

You hit the nail right on the head!!! I just unplugged the battery maintainer, turned the key and it primed!

thanks
John