Electric Fuel Pump Set Up

[PlumCrazy4spd]

Hey guys, unfortunately had an engine go on me at the end of the season last year, I purchased a reman and started switching all the peripherals over. When I got to the fuel pump I noticed the block had no provision for a mechanical pump. I ordered the Carter Marine Universal pump. Comes with the pump, the pigtail harness, the relay and a cheap filter. Electronics are not my strong suit on these. Where would you guys pull keyed power from and for the low oil pressure cut off, would you just run a tee off the back of the block and maintain the use of the stock oil pressure sensor and run the switch off the other part of the tee? Thanks in advance

 

[Sundancer]

That's what we've done on my son's ski boat. We just put in a "T" on the stock oil pressure sensor and ran the fuel pump off that. Haven't tested it yet, so I don't know if there is a delay before the pressure builds and sends current to the pump or not. I think that is a Coast Guard Reg these days, but I'm not sure and wouldn't claim to know that. I just happened to have read something along those lines. The Previous Owner didn't care about the coast guard or feeding a fire with fuel if he forgot to shut off the switch!! We're correcting that. I believe the oil sensor feeds the positive side of the pump. The other is just a common ground for the wire. Check yours first though!

 

[PlayDate]

This is what you want to use.


https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/fuel_system_components_and_service/fuel_pump_accessories/parts/12-810

 

[PlumCrazy4spd]

This is what you want to use.


https://www.holley.com/products/fue...nd_service/fuel_pump_accessories/parts/12-810

What is the third tab for on the switch? I see some with two and some with three. Thank you!

 

[PlumCrazy4spd]

This is what you want to use.


https://www.holley.com/products/fue...nd_service/fuel_pump_accessories/parts/12-810

That's how I initially had my schematic drawn up, unfortunately I read that you shouldn't pull power directly from the low oil pressure switch. I don't know if there would be an actual potential issue or not, just what I had read, This is my least favorite part about engines and their components. Thank you!

 

[PlumCrazy4spd]

Is this completely wrong?

 

[PlayDate]

This is how the Holley switch is wired:

https://documents.holley.com/199r9680-1rev.pdf

 

[hughespat57]

Is this completely wrong?

Pretty much yes this is wrong.
See the document @PlayDate attached from Holley.

The thing to understand is WHY the connections are the way they are.
the three way switch COMMON goes to the pump.
the N.C. goes to the starter SOLENOID wire (not the main battery lead) this will energize the pump during cranking when there is not yet oil pressure.
The N.O. will power the pump once oil pressure is up, and cut out if the engine stalls for any reason.

 

[PlumCrazy4spd]

Pretty much yes this is wrong.
See the document @PlayDate attached from Holley.

The thing to understand is WHY the connections are the way they are.
the three way switch COMMON goes to the pump.
the N.C. goes to the starter SOLENOID wire (not the main battery lead) this will energize the pump during cranking when there is not yet oil pressure.
The N.O. will power the pump once oil pressure is up, and cut out if the engine stalls for any reason.

Perfect thank you !

 

[DaveKamp]

Yep, that wiring scheme is rather important.

On an aside note, the reason for no fuel pump provision... is that a change in model year relegated the carbeurator to history-books... at least, in automotive/light-truck side of the industry.

The 5.7 prior to like... 1997 had a hole for mechanical fuel pump, and I think by late '98, GM stopped including the hole, but most of the camshafts still had the operating lobe. I don't recall the exact changeover time, but IIRC the blocks of '97 to mid '98 production timeframe (fitted with the MerCarb) had fuel pump holes. Those engines were Vortec (L31, not L05) with hydraulic roller-cam profiles.

If yours has the boss, and you have the patience to do so, you can chain-drill a path for the hole (using old block or fuel pump gasket as a pattern for a template) and then carefully keyhole-saw the opening, and remove the waste plug, carefully file the hole, and drill/tap the bolt holes, but you WILL have to contend with recovering metal fragments from inside (a magnet and some judicious rinsing).

The one 'gotcha' of the L31 (regardless of wether the fuel pump boss was open) is that the mechanical fuel pump pushrod length is SHORTER than a 'pre-L31' 350. One can actually get the mechanical fuel pump IN there, but the camshaft's fuel pump lobe will come around, and overtravel the fuel pump lever, breaking it, or the fuel pump base... so for anyone who does so, PLEASE make certain you have the proper (shorter) fuel pump pushrod correct for the L31 MARINE engine.

(The L31 in automotive trim NEVER came with a mechanical fuel pump... it was only used for marine use... and INTENDED to be used on any industrial L31 applications, but I don't think there WERE any... at least, not that used gasoline carbeuration. {natural gas and propane didn't need a fuel pump)

 

[PlumCrazy4spd]

Yep, that wiring scheme is rather important.

On an aside note, the reason for no fuel pump provision... is that a change in model year relegated the carbeurator to history-books... at least, in automotive/light-truck side of the industry.

The 5.7 prior to like... 1997 had a hole for mechanical fuel pump, and I think by late '98, GM stopped including the hole, but most of the camshafts still had the operating lobe. I don't recall the exact changeover time, but IIRC the blocks of '97 to mid '98 production timeframe (fitted with the MerCarb) had fuel pump holes. Those engines were Vortec (L31, not L05) with hydraulic roller-cam profiles.

If yours has the boss, and you have the patience to do so, you can chain-drill a path for the hole (using old block or fuel pump gasket as a pattern for a template) and then carefully keyhole-saw the opening, and remove the waste plug, carefully file the hole, and drill/tap the bolt holes, but you WILL have to contend with recovering metal fragments from inside (a magnet and some judicious rinsing).

The one 'gotcha' of the L31 (regardless of wether the fuel pump boss was open) is that the mechanical fuel pump pushrod length is SHORTER than a 'pre-L31' 350. One can actually get the mechanical fuel pump IN there, but the camshaft's fuel pump lobe will come around, and overtravel the fuel pump lever, breaking it, or the fuel pump base... so for anyone who does so, PLEASE make certain you have the proper (shorter) fuel pump pushrod correct for the L31 MARINE engine.

(The L31 in automotive trim NEVER came with a mechanical fuel pump... it was only used for marine use... and INTENDED to be used on any industrial L31 applications, but I don't think there WERE any... at least, not that used gasoline carbeuration. {natural gas and propane didn't need a fuel pump)[/QUOTE
It's already back in the, but wow you are a wealth of knowledge in the small block Chevy/mercs! That is impressive. I think I've got my mounting and wiring set up, I'm gonna try and get it all sorted tomorrow. Thank you for your input.