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fuel pump safety switch wiring
Posted: Fri Apr 17, 2009 10:07 am
by tunnel ram efi
I am using MSII with the relay board and cannot find a wiring diagram for the fuel pump relay and a oil pressure safety switch. I am using a 3 prong switch from a early GM, not the specified Holley switch. Is this not just a limp home feature if the relay fails? Thanks Rich
Re: fuel pump safety switch wiring
Posted: Mon Apr 20, 2009 6:33 am
by Matt Cramer
Usually you would use the MS to cut power if RPM drops to zero instead of an oil pressure safety switch.
Re: fuel pump safety switch wiring
Posted: Mon Apr 20, 2009 7:01 am
by tunnel ram efi
Why do GM tpi motors use this set up and what happens if the fuel pump relay quits? Rich
Re: fuel pump safety switch wiring
Posted: Mon Apr 20, 2009 3:01 pm
by Daryl
"Why do GM tpi motors use this set up and what happens if the fuel pump relay quits?"
First off, I don't know how GM used the switch. If the fuel pump relay quits, the fuel pump quits, and your engine quits. Replace the relay. There is no 'double safety' or 'limp' mode for the fuel pump.
With that said, if you wire the oil pressure switch inline with the impact switch, Your car will not start until there is oil pressure, and in the event of an oil system failure where you lose oil pressure, it will also kill the pump, possibly limiting damage to the engine.
Re: fuel pump safety switch wiring
Posted: Tue Apr 21, 2009 8:15 am
by tunnel ram efi
I am pretty sure that the oil pressure switch by passes the fuel pump relay to provide voltage to the pump in case of relay failure. I found out that GM no longer installs this feature, so nor will I. I was just trying to follow Megasquirts wiring instructions and get all the necessary wires in my harness before shrinking the tubing. I appreciate everyones help. I am sure I will need much more. Thanks Rich