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jersey280

Fuel pump primes constantly? HELP??

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Hey guys,

 

1978 280z L28E. Whenever I turn the key to any position forward the fuel pump runs constantly. Isn't it suppose to prime for a few seconds and then stop prior to turning the car over? Appears to be a replaced fuel pump by P.O looks relatively new. Any suggestions would be great. Thanks guys

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What position are you referring to? The behavior may have changed in 78, but in 77 there was no 'prime' functionality. The pump is triggered by the AFM flapper when the key is ON, and runs continually when the key is in START. I would start by investigating the AFM. Get a wiring diagram and a multimeter and start measuring.

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ZHoob is correct - there is no "prime" on these early EFI Z's.  Not on the NA ZX's either - not until the turbo engine (L28ET) ECCS ECU.  And the fuel pump SHOULDN'T run continuously - that means a very important saftey circuit has been disabled or is inoperable and needs to be corrected.  That's the switch in the AFM he referred to.  It's bypassed in the Ignition START position and power is passed to the fuel pump.  In any other ignition position, it's the AFM switch that should provide power to the fuel pump.  The logic being: IF air is passing through the AFM with enough velocity to make the vane move, the engine must be turning.  If the engine is NOT turning (running) the switch should be open and NO power should be going to the fuel pump.

 

If it doesn't work that way someone has screwed with the circuitry or the AFM is defective.  The switch in the AFM is pretty simple (and shouldn't default to ON) - it's more likely that someone has bypassed the safety feature...

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Good stuff here...but...Nissan changed to a different system in 1978.  And it had a flaw.  It uses the alternator power and an oil pressure switch to run the pump, but the flaw is that if the oil pressure switch is disconnected the pump will run when the key is on.  Check that.  And read the Engine Fuel chapter in the FSM it shows and describes everything.

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