JLeatherman

If I were to stop using my in-tank electric FP and switch to one mounted under the hood, how would I go about that? Can I operate an underhood FP with the existing relay? Anyone done this? Also, can I pull fuel through my in-tank pump or do I have to remove it and install a straight-through tube in place of it?

Mojave

Electric fuel pumps are much better at pushing fuel than pulling. Putting the pump that far from the tank won't make it happy.

JLeatherman

Scratch the under-hood part. The pump I was loking at, a Holley, is supposed to be mounted at the bottom of the tank. The wiring is still in question, however. The stock relay energizes for the "priming" phase and then shuts off until it receives a signal that the engine si running (oil pressure???). I want to wire in an external pump that runs when the key is on and stops when the key is off. Do I need to use a completely separate circuit with it's own relay? How would I then disable the stock circuit?

If you are wondering why I'm doing this, the car's return line was crushed by a previous owner at the jacking point. I temporarily repaired it, but it's a constant source of worry for leaks. Since the car is carbed now I don't need a return line if I use a lower-pressure extrenal pump.

And, can I in fact pull fuel through the stock pump while it's not running?

trackman44

I'm running an 84 corvette with stock pump (in tank) thru an adjustable FPR hooked up to a demon 650 double pumper. I used an automotive relay hooked up to the 4psi oil switch to turn on the pump. No problems starting her up or running her.

CFI-EFI

That is wrong. The stock pump resumes pumping, after the 2 second priming period when the ECM senses that the engine is turning, by means of cranking, and stays powered (because it is still turning) after it is running. It does not wait for the engine to start running or for the oil pressure to build. The oil pressure switch has nothing to do with it.



A pump directly wired to the ignition switch would actually run slightly more than the stock set up. I don't understand how that will alleviate the need for a fuel return line. To disable the stock pump wiring, disconnect the pump wire at the plug at the tank and tape it up. Another way would be to pull the fuel pump fuse. Have you looked at the wiring schematic in your FSM?



The amount of fuel pressure is not the reason for the return line. The low pressure used by a carb isn't all that much lower than the spec for TBI. Your time and efforts may be better spent doing a proper repair on that return line rather than trying to reinvent the wheel, to eliminate it. Also, the pressures in the return line are minimal.

I have never tried to pull fuel (electric fuel pumps are better pushers than pullers) through a dead electric fuel pump, but I can't imagine it not being a significant impediment to free flow.

RACE ON!!!

JLeatherman

The kind of pump eliminates the need for a return line. Such as this one (180-P4594):

http://www.jegs.com/webapp/wcs/store...48050_-1_10307

It's internally regulated and does not use a return line. Same as this one:

http://www.jegs.com/webapp/wcs/store...47713_-1_10307

CFI-EFI

To me it seems a shame to discard a perfectly good pump that will develop two or more (ten?) times the pressure for a low performance pump such as that, just to save doing a proper fix on the return line. Besides the $73.00 plus $10.00 - $12.00 handling, you still have to mount it, wire it, and plumb it. It seems to me you already have a better pump, in the ideal location, all wired and plumbed, save one crushed section of steel line. Its your car, your time, and your money. Have fun.

RACE ON!!!

JLeatherman

I'm intrigued by the 4psi switch/oil relay wiring. Anyone know how this is done? It would eliminate the priming/stopping part of the startup.

RacerX70CC

why create more work if you don't have to?

My carbed '85 project car has a TBI pump in place of the TPI pump, with a Mallory return style regulator (attached to the original OEM lines, utilizing the OEM fuel filter).

CFI-EFI

I know how it works. It is all explained in your FSM, and also in the many posts I have made explaining the fuel pump/relay/oil pressure switch operation. I don't understand what you mean by "how this is done". How is WHAT done? What is the "It" that "would eliminate the priming/stopping part of the startup"? Why would you want to eliminate the priming function?

RACE ON!!!