can you bypass a fuel pump relay ?

can you bypass a fuel pump relay ?

Postby webcat [OP] » March 19th 2009, 1:11pm

I have a toggle switch to turn the ignition on and then a push start button to start .
I was wondering if i could get rid of the fuel pump relay and just run 12volts to the pump from my ignition toggle switch ?
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Re: can you bypass a fuel pump relay ?

Postby headgorilla » March 19th 2009, 3:35pm

Sounds dangerous to me.......running the pump at 12v constant might burnout the pump....overheat?

I think the PCM controls the voltage.....I'm no fuel system expert but I might read up on that one...

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Re: can you bypass a fuel pump relay ?

Postby webcat [OP] » March 19th 2009, 4:04pm

1988 chevy van TBI


i just found a little more info : When the engine is running the ECM looks for oil pressure, if there is no pressure or very little, then the ECM automatically shuts engine down to save it from self destruction of the crank bearings.


ah guy from four wheeler magazine said
Some people bypass the oil pressure switch, I didn't , so if the motor loses Oil Pressure , the fuel pump quits.
another guy said
i think i will bypass my oil pressure switch and just run a light that lights up if i lose pressure , then i will turn the car off manually if it light lights up
leaves one less thing to make my car not start



more info
The Fuel pump relay powers the pump momentarily at start up, independently of the oil pressure switch.

During the start cycle there is a fuel pump relay that takes over to run the fuel pump
After the engine is running that relay turns off and the current for the fuel pump is supplied via the oil pressure sending unit If that relay fails then the car won't start until the oil pressure is up to three or four PSI.


i found this at third generation camaro
Cut the Tan/White wire after the common tie point so that you are only
controlling the fuel pump with your switch. Leave enough length on the
cut side in case you ever want to mate the wires back to stock.

If the 3rd gen is the same as the 4th gen, the relay is located behind the
driver's side kick panel (near the hood release lever).

I would suggest connecting the switch to a source which is dead when
you remove the key (switched power) in case you forget to flip the power.

it looks like i found my answer any body have any info chime in




the schematic below is a before picture
after i remove the oil psi switch and fuel pump relay and fuel cycler module and all there associated wires i will modify the schematic and post it
just simplified the circuitry that much more

the second schematic is from third generation camaro showing how they did the mod
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Last edited by webcat on March 20th 2009, 8:24am, edited 1 time in total.
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Re: can you bypass a fuel pump relay ?

Postby Matrixx » March 20th 2009, 12:40am

Personally, I would leave all the built in safety features alone and try to find another work around if you could. Just a comment and a thought.:)
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Re: can you bypass a fuel pump relay ?

Postby astro355 » March 20th 2009, 12:49am

Why would you want to remove the fuel pump relay?

You can wire a switch in series with the relay so you can manually control the fuel pump.
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Re: can you bypass a fuel pump relay ?

Postby webcat [OP] » March 20th 2009, 8:21am

i'm making custom wiring harnesses and trying to make them as simple as possible , if i dont need somthing to make the car run right , i dont want it in there
i've already removed egr ,smog pump ,carbon canister cat convertor , and replaced the ignition switch and removed all of its wiring and replaced it with a toggle switch and a push button starter , its pretty sweet because when you look under the hood it looks more like the older hot rod cars , real clean , not a bunch of wires and hoses going every which way , runs and sounds alot better too!
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Re: can you bypass a fuel pump relay ?

Postby txturbo » March 21st 2009, 2:23am

and now you've defeated all the safety features and no longer comply with emission laws. If you are ever in an accident and/or roll over, that fuel pump is going to keep pumping fuel until the it sucks air. You better hope a fire doesn't start and you kill yourself or others. Those circuits are there for a very good reason.
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Re: can you bypass a fuel pump relay ?

Postby astro355 » March 21st 2009, 1:51pm

txturbo wrote:and now you've defeated all the safety features and no longer comply with emission laws. If you are ever in an accident and/or roll over, that fuel pump is going to keep pumping fuel until the it sucks air. You better hope a fire doesn't start and you kill yourself or others. Those circuits are there for a very good reason.

:goodpost:

The other reason why you want to use that fuel pump relay is because its a relay. Relays are designed to handle high voltage and/or amperage. You don't want to send high voltage thru a switch, it will burn it out. You wire it so the switch (using low voltage) activates the relay which in turn activates the pump. The pump has a high current draw (while the relay has a low current draw) which would try and suck that circuit right thru your switch. It would not only burn it out, it would stall your van, possibly damage your fuel and cause a fire.
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Re: can you bypass a fuel pump relay ?

Postby webcat [OP] » March 21st 2009, 6:00pm

I always thought of a switch as just metal contacts , either there open or there closed .
So lets say when you close the switch , would'nt it be just a closed circuit ? what i mean by that , the switch is just 2 metal parts you touch to each other to complete the circuit , so how could it burn out?
let me know if i'm over looking something
i could see how other stuff in the circuit would burn out though.
I was just thinking i have a momentary push button switch on my starter circuit and when you push the button around like 500 cranking amps goes through this switch and it never burns out . Its basicly works the same way as crossing the starter over with a screw driver . Just thought i would use that as a example.
I'm not saying you could put 500 cranking amps through a standard 12 volt 30amp switch , I'm just saying it would work in a simular fashion , connecting battery voltage to one terminal and ignition to the other of a standard 30 amp switch should'nt be a problem as i've had mine hooked up that way for 2 months and hav'nt had any problems.

As far as my first question about if i could run without a fuel pump relay , i relize know that was a pretty stupid question , i should of known i could'nt
i dont know what i was thinking because as i thought about it more i started thinking it would be about the same thing as trying to run a heater blower motor without a relay , and i would never try that . what the hell was i thinking :banghead:
thank you Astro 355 for reminding me of the fuel pumps high current draw .

Thanks for all the info guys and keeping us safe. looks like i'll have to keep the relay.
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Re: can you bypass a fuel pump relay ?

Postby astro355 » March 21st 2009, 10:27pm

Here's the thing. With the push button start, how long are you running 500 amps thru that button? Also, on the other hand, you're not running 500 amps thru that button. The button activates the solenoid in the starter, which also acts as a relay. You have low current thru the button controlling high current going thru the starter.

Secondly, buttons are not usually made that heavy duty. When the current exceeds the rating, it melts the terminals inside the button. That's why when you wire up electric pumps, solenoids, etc, you use a relay.
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Re: can you bypass a fuel pump relay ?

Postby webcat [OP] » March 21st 2009, 10:32pm

Astro 355
i went and found a schematic showing how relays work , looked it over and thought about what you said
and it's all clear now
you explained how it works very well Thank you
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Re: can you bypass a fuel pump relay ?

Postby astro355 » March 22nd 2009, 2:03am

Glad I could help.
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