Sonix

iTrader: (1)

Hey guys, I want to add an electric pump back at the tank, to try and resolve a higher RPM fuel starvation issue i'm having.
I have a stock replacement mechanical pump on the block, and I want to add the Summit knockoff of the Holley red pump G3136-1. $79 vs $105.

Will this work correctly? I'd basically be simply pressurizing the fuel line. I don't need a regulator or anything for this right?

Thanks

Apeiron

The mechanical pump already has a regulator built-in. I don't know that would solve whatever problem you're having.

Sonix

iTrader: (1)

That's what I was thinking, pumping into the mechanical pump would do the fuel regulation. Does this mean I could use the bigger pump, the 14psi one, since the mech pump will regulate it down? (knockoff of holley... black I think?)

I ran out of fuel pressure at higher RPMs. I ran a "t" in front of the carb to a fuel pressure gauge taped to my window and saw the 0 psi pressure. I replaced the pump with a stock replacement one. A few weeks later the problem seemed to be back (or never left, hard to tell). Haven't hooked up a gauge yet, but i'm fairly confident it's the same thing.

I believe F-bird recommended using an electric pump to pressurize the lines, and help avoid vapor lock (fuel boiling in the lines, etc). My fuel line runs ~3/8" away from my passenger header, and I can't get it any further away. It is a return style mech pump.

I don't want to replace this mechanical pump again for fear of the problem never leaving. I thought the electric might save me.

Sonix

iTrader: (1)

Ok, I think i'll give it a try. If nothing else, i'll have a nice electric pump for a nitrous setup down the line, or for my next carbed car

F-BIRD'88

Install the electric pump and remove the mechanical pump. (in our cars it picks up a lot of heat). Reroute the fuel line.
I know its a pain to do that. If you spend the time to build a good rubber isolated suspended fuel pump bracket to mount the electric pump, it won't be too loud. The 7psi pump won't need a regulator. Make sure the pump gets a full 12volts power. Check any rubber hose on the feed side of the pump. They tend to collapse. I'd also pull the tank sender unit and check the in tank pick up tube.
Should have a flaired end (tube flairing tool) or at least cut the end of the pick up tube on a angle to maximize fuel flow.

Sonix

iTrader: (1)

Remove the mech pump? I thought it would be best to leave it in place?
This way I could (easily) leave this as a return style fuel system.

There's a flexible rubber line between the pump and chassis of the car. Since the tank is mounted solidly, can I replace this with a hard line somehow?

I'm not too wild about dropping the tank on my '82 car I'm pretty sure the pickup is ok...

Apeiron

I wouldn't count on it, with potentially 26 years worth of cruft and mung sticking to your strainer sock.

naf

iTrader: (7)

I've run an electric through a non-functional mechanical pump in order to retain the fuel return without a fancy bypass regulator or re-routing stock fuel lines. It does pick up some heat but no more than a stock system... and fuel is constantly flowing. Put the little Summit (or was it Jegs?) knockoff in back, 'course my '87 still had the stock in-tank pump working but I wasn't getting a decent pressure reading off it alone, maybe 1-2 psi?

I'd try it through the mechanical then maybe re-route later if you feel the need.

Supervisor42

Remember if "Mr. Old-school" (me) doesn't run a mechanical pump, it's time to say goodbye to it. If you buy an electric pump, get a blockoff plate too because the only job the mech will have now, is to fill the crankcase with gas if the diaphram breaks. (goodbye bearings)
If you bite the bullet and setup a bypass regulator with a return, the fuel is constantly flowing back to the tank so it can't get too hot. There's plenty of extra lines going back to the top of the tank.
You will also be able to easily "flow-test" the system by sending the return flow into a container to get 'gallons-per-minutes' at a set psi.
Try doing that with a mechanical

84noname

ive been wanting to do this since i always have to pump my gas alot to start my car. this will go away with a inline electric fuel pump right? i already have one. could it be mounted on the firewall someplace and be ok. its like a knock off made by purolator small square one

Apeiron

No

naf

iTrader: (7)

That's not a concern for me. No fuel pump rod bore. I don't even need the 'sofakingdom' bolt. Something to consider otherwise.

84noname

so whats the cause? i usually only have the problem when i first start the car after a while of not driving it. crappy carb?

Damon

I run low pressure electrical pumps into a block-mounted mechainical pump all the time. Done half a dozen of them now. It's a fantastic combo for helping out a mechanicial pump when it just can't keep up on it's own.

I have run Holley Red pumps into stock pumps and Carter 6 PSI street pumps (that's my current favorite combo). I've also used the Carter 5 PSI electrical pump into a Carter 6 PSI street pump. Also works well but the Carter electrical is noisier than the Holley by quite a bit.

The electrical must have about the same pressure as the mechanical pump or it will just unseat the one-way valves in the mechanical pump and outrun it. DON'T use a high pressure electrical back there like a Holley Blue.

Mechanical pumps, like all fuel pumps, are great at pushing fuel but not good at sucking it. While the GPH rating on a mechanical is probably more than you'lll ever need it to be, they just can't do the LONG draw from the tank very well. You often find they just can't keep up at the top of 1st and 2nd gear where fuel demand is highest and acceleration is highest.

Adding a low pressure electric is a fantastic way of greatly increasing the fuel flow of your whole fuel system. I have personally seen on 2 occasions where the mechancal pump alone can't keep up with demand running as slow as high 13s. Add an electrical helper pump and it holds rock-solid fuel pressure all the way into the 11s, with no other changes. And if either pump goes south on you, you can still drive the car home on the other pump.

Don't use just a low pressure electrical by itself- fuel pressure way up front by the carb will fluctuate considerably under hard acceleration. But use it in combination with a block-mounted mechanical and fuel pressure is rock solid- often fluctuating no more than 1/2 PSI under any condition.

I use this setup on my 78 Malibu with the mild roots-blown 383 under the hood. Without the electrical helper pump the engine will basically shut off from lack of fuel around 4500 RPMs. With the electrical in place it's rock-solid at 6 PSI all the way to 6000 RPM redline (470HP, dyno verified, 390 at the rear wheels, also dyno-verified). And I'm still using all the factory 3/8" fuel lines and stock tank pickup. The difference is dramatic.

All of this stuff I'm wirting about has been verified by me putting a fuel pressure gague on the car (where I can actually see it when driving) and actually driving it around and making runs. No "theory" or "this is what should happen" kinda stuff posted here.

Also, please note that the FACTORY used a low pressure electrical in the tank in combination with a block-mounted mechanical pump on the engine- 3rd gen F-bodies with the L69 305 HO carbureted engine got this kind of setup from the factory.

Do it!

84noname

so does my 84 have a low pressure near or in the tank?
and how do i tell if this inline pump i have is high or low pressure?

naf

iTrader: (7)

One likely cause is leaking fuel well plugs that allow the fuel bowl to empty while it sits. Then the motor has to turn over for a while before the bowl refills. An electric helper would mask this problem but not fix it. Could also, however, be a bad/old accelerator pump that is not putting a full shot of fuel into the intake. Both those suppositions are carb related and a rebuild would fix.

If you have an LG4 and it's an '84 chances are it does not have the in-tank electric helper that was later installed by the factory to fix some fuel delivery issues. So the helper pump at the rear wouldn't be a totally bad idea even for a stock setup. Though I probably wouldn't do it until I'd experienced problems.

Sonix

iTrader: (1)

Huh, great, I've got a perfectly split crowd here
Well since i've got the rear end out still now, It's just not much more of a job to drop the tank, so I might check that out and inspect the pickup.

Also, i'll look at mounting the pump right where the rubber fuel lines go from tank -> frame at the drivers side there. I think that'd be the easiest place to mount it, and easiest way to couple it from whatever NPT threads are on the pump, into a 3/8" hardline via all kinds of adapters.

Thanks, i'll post back after the thaw when I get this done.

Apeiron

With a return-style mechanical pump that shouldn't be a problem.

Damon

84 might or might not have the factory electric helper pump. If it was an original L69 engine car it should have one. It will be IN the tank if it's got one- looks very similar to a fuel injection pump setup.

With an aftermarket electrical pump mounting it close to the tank wherever is convenient is perfectly acceptable. That's where I mount them.

Not sure if a factory return-style mechanical pump would work with a high pressure electric pump. The return is a very small restriction in the pump- it could easily be overwhelmed with too much volume and not be adequate to regulate a high pressure pump (Holley Blue) down to carb-friendly levels during periods of low demand (idling, light throttle driving). Best to keep the electric's pressure close to that of the mechanical pump.

2oldFbody

Damon with the electric and mech. pump set up can you just run the mec. pump on the street while cruising and pull the fuel thru the elc. pump.

Apeiron

What would be the point of that?

Damon

Sure can. Don't expect to be going beyond 3/4 throttle and ~4500-5000 RPMs without encountering fuel starvation (the pump is still a restriction when not running), but you can absolutely drive around normally, even aggressively, without any problem.

I've had times where my relay died and I drove around for a long time before I realized the electric wasn't even running. Only when I laid it out did I get the familiar "shut down" well short of my shift RPM.

2oldFbody

If a guy wanted to he could wire a 3 position switch to the fuel pump relay,
with one side running to a full throttle limit switch so the pump would turn it
self on at full throttle. The other side would be constant on for the race track.

Damon

Ya, true. Or you could just run it all the time like I have for 6 straight years of weekend fun (mostly street driving, occasional trips to the track) and still never have a problem. It's pretty damned bulletprooof. Make sure you use adequate wiring to power the pump with good electrical connections and they last close to forever.