Thread: Fuel question
View Single Post
mark houghton mark houghton is offline
Registered User
mark houghton's Avatar
Join Date: Jul 2008
Location: Central Washington State
Posts: 3,776
Originally Posted by lucittm View Post
I believe there is circuitry in the fuel pump relay wiring to allow the fuel pumps to run for 5 sec. or so at startup. Otherwise there would be no fuel pressure to start the engine. This may be why your engine starts and then dies.

On my car, I have the connector on the air meter but it is not connected to anything because of an update to the circuit wiring. My understanding of this switch is that it cuts power to the fuel pumps if the plate is in the upper position and the key is in the "on" position but the engine is not running.

I don't know of any such circuitry that runs the pumps independent of the metering plate arm being deflected...other than a short micro second of run time that some of us seem to experience (I think as a function of the yellow relay which probably has a capacitor which takes time to "ramp up" and allows the pumps to run briefly when the key is first turned to the ON position). In theory (and we're all learning theory with these cars....thus, this forum) the action of cranking the engine and drawing air across the metering plate is what deflects the arm enough to trigger the switch and start the pumps. That all happens immediately upon cranking the engine if everything is functioning correctly. Residuall fuel pressure residing in the fuel accumulator deminishes the wait time for pressure to build.

You are correct about the built-in the safety feature of the pumps not running with the plate at rest. Get in a car wreck and if the engine stalls, so do the pumps. Run with your plug un-plugged and you're bypassing the safety feature.

Just my understanding, anyway.
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 08-18-2010, 08:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #28 (permalink)