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Username Post: why use relay
Senior Member
Posts: 415

Loc: Tracy, CA
Reg: 07-18-00
01-21-20 01:51 PM - Post#2784828    
    In response to george88gta

  • george88gta Said:
  • bobb Said:
for an electric fuel pump i would always run a relay so that oil pressure is needed to turn it on. yes its more complicated but still simple wiring. reason is that in case of emergency, when the engine is off so is the fuel pump, avoiding a bigger emergency.

That's kind of where I was heading. I will admit, that a long time ago ( 6 volt 51 Mercury) I did wire an electric fuel pump to a switched circuit. If I remember correctly, my 1988 GTA ( fuel injected ) used a relay. For the initial turn of the ignition switch, you got a timed pulse to the pump. After that, it relied on the oil pressure to control the relay and activate the pump. Ford also had an impact switch that would cut off the fuel pump.
Bottom line is that it is safer to use a relay.

Yes, your GTA fuel pump used a relay but it didn't run through the oil pressure switch.

Only carb'ed 3rd Gen F-Bodies (VIN G and H) fed 12v to the electric fuel pump through an oil pressure switch (OPS) only after the engine was running and the key returned to the run position.

The fuel pump relay was closed (by passing the OPS) only while the starter was engaged.

There were both electric and mechanical fuel pumps; an odd setup for a carb'ed engine. The only explanation I have is this was done to address vapor lock issues.
1987 IROC-Z 5.0L
1992 Lumina Euro 3.1L
2003 GMC Safari

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