Fuel Pump Relay?

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Fuel Pump Relay?

Postby vegastre » Sat May 17, 2014 11:56 pm

I should know this?
Looking at the wiring diagram it looks like a stock H-Body does not require a relay for the fuel pump. Ya know, I'm not even sure how the electrics work on the fuel pump/oil pressure switch? Anyway my question is does our cars require a fuel pump relay? I would think they would but what do I know =)
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Re: Fuel Pump Relay?

Postby stage169 » Sun May 18, 2014 5:46 am

No relay needed. Cosvega76 (Chuck) lays it out here viewtopic.php?f=44&t=41060
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Re: Fuel Pump Relay?

Postby vegastre » Sun May 18, 2014 1:46 pm

Jimineee...
No wonder I couldn't figure it out. Actually I did at one time lol. A safety deal for sure I would like to keep. So...question? can I use this with my Multi port EFI high pressure fuel pump? When the ignition key is turned to the on position will the fuel pump energize instantly and pressurize the fuel rails instantly for starting and oil pressure? Both? Separate of course from the computer fuel pump command and relay? Which I guess the computer has it's own fail safe built in to some sensor? Which to use? The point, you can't have high pressure gas spewing everywhere in case of a wreck. Almost as important is saving the engine from damage if oil pressure is lost just cruising down the highway. The ECM I'm using does not manage oil pressure.
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Re: Fuel Pump Relay?

Postby Monza Harry » Sun May 18, 2014 6:15 pm

Phil if you are using the stock fuel pump that circuit does not need a relay, I seem to remember my fuse for the pump only being a 1 or2 amp (I do sometimes suffer from CRS, ask my wife :lol: ) you can use that as a pre-delivery pump as your new FI swapped engine will need a High Pressure pump (40, 45# if I had to guess*) which you could mount up front and I would expect that pump too have a better electrical appetite (5 to10 amps) and that should use a relay. As for merging the two systems that will need a little more thought, and maybe some diodes or multiple relays to prevent any possible back feeding situations that could arise. Harry
*I didn't think about yours being pressurized, so yes it would need a even higher pressure pump as you state ahead
Last edited by Monza Harry on Sun May 18, 2014 9:52 pm, edited 1 time in total.
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Re: Fuel Pump Relay?

Postby vegastre » Sun May 18, 2014 8:08 pm

Right Harry,
I have a high pressure pump 90 PSI from mid 90's S-10 which is the exact size of the stock H-body pumps. If I was using one of the new design EFI pump set ups I would use a relay. At this point I think I'm going to try out the H-Body fuel pump/oil pressure wiring circuit and see what shakes out. Real world testing will quickly tell me the weak link in the chain. It's just that looking at the Factory wiring diagram was a bit confusing not seeing a relay in the circuit.
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Re: Fuel Pump Relay?

Postby stage169 » Sun May 18, 2014 8:12 pm

I agree with Harry stock pump no relay. New pump you should start with its continuous amp draw rating and build the circuit from there. This first schematic is from a car magazine and your oil pressure switch is already wired this way. Add a relay rated for your pump with the correct gauge wiring and you will have the same protection as stock.

I did the second schematic after listening to Chevyart and Spence. Just something to look at Chevyart was needing a carb prime switch but wanted to keep the stock oil pressure switch too. Looks like the stock fuse is 10 amps (Harry I didn't remember either) but I wouldn't push the stock wiring unless your new fuel pump amp draw rating is half that. This circuit would shut the pump off even if you left the manual switch on since its power is off the ign terminal on the fuse block. Handy if your oil pressure switch fails you can flip the switch and drive home. I pulled some junkyard relays and diodes to do this someday.

Brian
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Re: Fuel Pump Relay?

Postby cosvega76 » Mon May 19, 2014 8:01 am

Phil,

If you're using an OE computer, you won't need the OP safety circuit. The factory programming primes the pump at startup, as you mentioned, and also monitors the crank trigger/distributor pickup coil for RPM. If the engine stalls the computer will shut off the pump.

I would suspect that even the aftermarket fuel injection controllers work in a similar manner, for safety.


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Re: Fuel Pump Relay?

Postby vegastre » Mon May 19, 2014 12:26 pm

If the engine stalls the computer will shut off the pump.


That's good news and what I had figured,
I may delete the OP switch altogether because it has given me night mares down through the years from springing leaks to coming unplugged, etc. Repeating myself, when I looked at the stock FP/OP wiring schematic I got so confused and paranoid. Although common sense should prevail you really have to consider everything and the reason I'm running this by you guys. It may seem simple but at this point nothing is simple when blending new with old. I have in the past and will continue to run my mechanical oil gauge.
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Re: Fuel Pump Relay?

Postby vegastre » Mon May 19, 2014 12:58 pm

Add a relay rated for your pump with the correct gauge wiring and you will have the same protection as stock.


Thank you,
Great schematics, right, absolutely...Done deal. When I was using a carb I often needed the 'fuel prime' option. Leaky fuel bowl gaskets and such.
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Re: Fuel Pump Relay?

Postby vegastre » Sat May 24, 2014 12:53 pm

After much thought:

1) Airtex 3270 pump 60 GPH at 70-90PSI for Vortec & LS applications.
2) Relay and PCM command to turn pump on and off.
3) Use existing H-Body 5/16 feed and 1/4 return.
4) Use MPI barricade fuel line rated at 225 PSI with seamless pinch clamps.
5) Steel can fuel filter located at rear of car.
6) Inline fuel pressure block and gauge at Supercharger.
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