Triggering Elec Fuel pump on Carb Eng - Team Camaro Tech
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post #1 of 7 (permalink) Old Dec 8th, 06, 03:36 PM Thread Starter
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Triggering Elec Fuel pump on Carb Eng

I installed a new engine with Mallory electric fuel pump last winter. I have a clear fuel filter in engine compartment ( force those interested, there is also Napa fuel filter ahead of fuel pump and SMI Q-jet has fuel filter ). The clear filter was originally installed to allow me to view status of fuel to carb. Well, what happens is that if the car sits a long time, the clear fuel filter willbe empty and ( since I have oil pressure safety switch on fuel pump feed ) I have to crank it for awhile to build oil pressure before fuel pump engages and primes carb and car starts. What I am thinking to do is to tap the fuel line trgger wire off of the crank circuit, using a diode, so that the fuel pump will be triggered as soon as I attempt to start the car. The diode should prevent feedback to the cranking circuit. If not a diode, I could use a relay. The question is, does anyone see a problem with this logic? On 2 other cars with q-jets and mechanical fuel pumps, I do not have this problem.
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post #2 of 7 (permalink) Old Dec 8th, 06, 04:49 PM
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Re: Triggering Elec Fuel pump on Carb Eng

Transfer the power to a dedicated fuel pump relay so when ign switch is in the ACC position, still powered when in IGN, the relay gets energized and power goes to the fuel pump.

Now when you select ACC, the pump will work and you can "hear" it load up, and fill the bowls. Now, carb full, go to START, engine does start, ign switch back to IGN, pump still runs as normal.

Priming carb is done. Also, passes NHRA Tech inspection, when ign is off, pump quits.

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post #3 of 7 (permalink) Old Dec 8th, 06, 06:34 PM
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Re: Triggering Elec Fuel pump on Carb Eng

If you're using the Holley 12-810 safety switch the problem is easily solved. The NO (normally open) terminal on the pressure switch gets wired to IGN terminal on the fuseblock. The NC (normally closed) terminal on the pressure switch gets wired to the start post on the starter solenoid (closest to engine with purple wire). The C (common) terminal on the pressure switch gets wired to the fuel pump or the pump relay coil +. The pump will run as soon as you start cranking. When the oil pressure comes up the ignition circuit will keep it running.

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post #4 of 7 (permalink) Old Dec 9th, 06, 03:33 AM Thread Starter
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Re: Triggering Elec Fuel pump on Carb Eng

Thanks guys, I see what you are both saying .. I should have said that this is a 55 Chevy, so I have no ACC position .... , but 12run, I think you have pointed me in the right direction ... I was trying to avoid any kind of feedback that would have kept the starter spinning ... I am running a remote solenoid which has the ignition post, so a hook-up as you suggest should be rather straightforward ...
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post #5 of 7 (permalink) Old Dec 10th, 06, 10:13 AM
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Re: Triggering Elec Fuel pump on Carb Eng

If you hook it up the way I explained it should work as intended. I'm not a big fan of hooking fuel pumps up without an oil pressure switch. It can be very dangerous. If you crash (God forbid) and the fuel line ruptures and the pump stays running you could get barbecued. It happened in my area years ago and the outcome was not good. I still catch people wiring fuel pumps directly to the ignition or a toggle switch and when I do I preach like a reverend on Sunday.

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post #6 of 7 (permalink) Old Dec 10th, 06, 02:31 PM Thread Starter
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Re: Triggering Elec Fuel pump on Carb Eng

Quote:
Originally Posted by 12run View Post
If you hook it up the way I explained it should work as intended. I'm not a big fan of hooking fuel pumps up without an oil pressure switch. It can be very dangerous. If you crash (God forbid) and the fuel line ruptures and the pump stays running you could get barbecued. It happened in my area years ago and the outcome was not good. I still catch people wiring fuel pumps directly to the ignition or a toggle switch and when I do I preach like a reverend on Sunday.
Did it today ... worked like a charm ... Thanks for the assist. Yeah, I agree that I wouldn't run an elec fuel pump without the pressure switch for safety. Thanks again ... sdt
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post #7 of 7 (permalink) Old Dec 10th, 06, 05:39 PM
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Re: Triggering Elec Fuel pump on Carb Eng

Your welcome.

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