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Electronics Need help wiring something up? Thinking of adding an electrical component to your car? Need help troubleshooting that wiring glitch?

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Old 02-13-2012, 08:49 PM   #1
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Location: Ocean City, MD
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Car: 91 rs
Engine: Carbed 355 CR 9:1 xr276 cam
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Fuel pump relay direct 12V current

After switching from TBI to Carb I have my fuel pump relay ( grn / wht) wire spliced and hooked directly to an Ign source on my fuse block, with a 20 amp inline fuse between the relay and the fuse box. I have two questions:

1) Will it hurt my fuel pump to be constantly on

2) I would like to hook up a toggle switch between the relay and my fuse box so I can shut off my fuel pump in case of an emergency (now when the key is in the on position the fuel pump is pumping). I would like to know if this would work to shut the fuel pump off and if this would be the easiest way to do it?
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91 CAMARO RS Carbed 355
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Old 02-13-2012, 11:57 PM   #2
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Re: Fuel pump relay direct 12V current

Quote:
Originally Posted by THETANK View Post
switching from TBI to Carb
1) Will it hurt my fuel pump to be constantly on ?
Are you still using the return line? (bypass reg )
In tank pump is not designed to be dead headed ( no return ); requires constant fuel flow through it to keep it cool

Quote:
Originally Posted by THETANK View Post
2) I would like to hook up a toggle switch so I can shut off my fuel pump in case of an emergency
I would like to know if this would work to shut the fuel pump off
and if this would be the easiest way to do it?
Would work but if you have time to flick the switch , surely you would have time to turn the key off?

If you wanted to do it right
you would use the original OP switch to run the pump directly as it did with the TBI setup and have the pump relay operating off a push button switch for priming only.

In most cases unless standing a long time , a carb engine will start on what fuel is in the fuel bowls and as soon as the engine fired, the OP switch would turn on the pump ( closes at 4 psi so would run pump while cranking over )

With a old skool mech fuel pump, you get no fuel flowing to carb until the engine is cranked over anyway
so you would be no different except for the ability to prime if carb lost fuel

In reverse , if engine stopped for whatever reason , OP would drop and the switch would kill the pump automatically

Last edited by vetteoz; 02-14-2012 at 01:21 AM.
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Old 02-15-2012, 05:46 PM   #3
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Re: Fuel pump relay direct 12V current

What is the advantage to having a push button to prime vs having a 12v wire hooked to the relay?

Basically now when I turn the ignition to the on position fuel is flowing to the car so if I switch the key to on for a few seconds before cranking the engine wouldn't that serve the same purpose as the push button for priming?
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91 CAMARO RS Carbed 355
14x3 open element
FLOWMASTER CAT BACK
straight pipe
LOW TEMP THERMOSTAT
HEDMAN HEADERS
Kyb shocks & struts moog springs
tds wonderbar
Spohn subframes
Tubular LCA's
Tubular panhard
3.42 gears & posi
Poly bushings
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Old 02-15-2012, 07:53 PM   #4
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Re: Fuel pump relay direct 12V current

Quote:
Originally Posted by THETANK View Post
I turn the ignition to the on position fuel is flowing to the car so if I switch the key to on for a few seconds before cranking the engine wouldn't that serve the same purpose as the push button for priming?
You said you wanted to solve the problem of the pump running full time when the key is on ; such like when the engine stalls.

As noted ;
in most cases a carb engine will start on the fuel in the carb alone so you don't need to prime the carb
so pump running before engine start does nothing
Would only use prime if car has been sitting for days or if you had a hot sink problem where fuel has evaporated from the carb.

Carb engines with a mech pump don't have a prime function; you just crank the engine over until you pump fuel up to carb
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Old 02-15-2012, 08:43 PM   #5
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Re: Fuel pump relay direct 12V current

Oh ok I misunderstood, so if the car were to stall with the relay hooked up to the OPSU the pump would also cut out because the oil pressure has dropped.

I appreciate all of your help I am a bit challenged (to put it nicely) when it comes to wiring/ electrical issues.
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Old 02-16-2012, 12:11 AM   #6
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Engine: 383 SP EFI /383 LT1 /L98 TPI
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Classifieds Rating: (13)
Re: Fuel pump relay direct 12V current

Quote:
Originally Posted by THETANK View Post
, so if the car were to stall with the relay hooked up to the OPSU the pump would also cut out because the oil pressure has dropped.
Like the factory setup you run the OP switch direct to the pump bypassing the relay ;
that way relay only runs the pump when you want it to ; say with a switch

Quote:
Originally Posted by THETANK View Post
I am a bit challenged (to put it nicely) when it comes to wiring/ electrical issues.
Easy
At the pump relay you have a hot wire direct from the batt that goes through the relay to the pump ( when relay operated )

Run a wire from that hot wire terminal to the OP switch and back to the wire/ terminal at the relay that goes out to the pump.
(It was already wired with the TBI but you probably ripped it out with carb swap)

Click the image to open in full size.


Push the button , relay closes. pump runs only while switch held
Crank engine , OP switch closes , pump runs fulltime ( relay bypassed)
Stop engine, OP switch opens , pump stops.
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Old 02-16-2012, 12:11 AM
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