Fuel pump swap, what involved?

[landpro00]

Hello again everyone!!!

First let me start by telling you what I've done so you know why I'm thinking of swapping pumps. About 6 months ago know, I swapped out my fuel injection, reluctantly, to a carb setup on my '88 with 454. About 2 weeks ago I had to replace the fuel pressure regulator originally installed, a Holley, with a new Mallory(MODEL MAA-4309 at Summit) one after the Holley one blew its seal from the pressure.

Hooked up the new Mallory regulator to the fuel supply line the Holley was attached to and then hunted and found another line that the shop that did the swap out had plugged and assumed it is the return line. If anyone could verify that one of the 2 lines connected to the throttle body is a return line that would be great!

Last week not sure yet, but i think, my tank switch valve went out. So was wondering if sending 44 PSI fuel pressure(50 PSI from pump,minus 6 to the carb) back to the switch valve through the return line could have been to much for the switch. I would think it would have been getting about the same return line pressures with the original setup or was pressure reduced somehow as it made it's way through the throttle body and back out?

Well, hope ya'll are still with me, I know this is kinda long but trying to give as much detail as I can!!!

My MAIN question is this: How hard would it be to swap out the factory fuel pumps in the tanks, with some lower pressure aftermarket electric pumps? Do the factory fuel pumps(in tank models) in older or non-fuel injected trucks have lower PSI pumps in them and would it be an easy swap out? Or would I have to, say, mount two electric pumps under the hood and somehow tie them in to the factory hoses and wiring so my tank select switch and fuel gauge still work?

All input GREATLY appreciated!!! THANKS!!!

Anyone else attempted this before? If so, how did it turn out?


Scott

[Captkaos]

Reading this, I am confused here. What is on the setup now? Carb, or TBI?

An 88 TBI pump will only have 13-18 psi tops. The is a supply AND a return line at the back of the throttle body. I have ran a 14psi pump on a carbed motor (no mechanical mount) and ran a regulator on it to get the pressure down to 6, and it ran fine.

[landpro00]

Swapped from a TBI to a Edelbrock carb.

Just looked at my Chiltons manual and it says ALL V8's starting in '87 have fuel pressure ranging from 35-47 depending on engine. For a '87 454 it says 34-46PSI.

It does have a little footnote number beside it( a 9 with a circle around it), but when you look down to see what it means it says "Carburetted: 5.0". Can't figure out why it would have that footnote beside a spec. line for a 454, LOL. It has the same footnote on all V8's( 305, 350 & 454).

On yours, was it originally TBI? What year?

THANKS!!!

[Captkaos]

On TBI models the pump could be a 30psi in the tank, (I am thinking it was more like 20-25) but the TBI had a regulator on it to keep the pressure between 13-17. If you put an external regulator on it, it should work fine.

I am still a little confused here, but the pump in the tank should go to a switch that selects the tanks. From there a supply line got to where the TBI was mounted (at the back of the firewall) from the TBI, a return line should go back to the tank/s. It shouldn't go back to the switching valve. The whole system would have the full pressure on the components up to the inlet on the TBI. The outlet side you would see the pressure drop. I would think the Switch went bad because of the age, or the lack of use over time.

The one we installed was a '78 pickup with a mechanical pump that we swapped motors from a '90 model which doesn't have the mechanical mount drilled/opened. We installed a electric pump that flowed about 25psi and ran a regulator on it to get it down to 7psi.

Originally Posted by landpro00

Swapped from a TBI to a Edelbrock carb.

Just looked at my Chiltons manual and it says ALL V8's starting in '87 have fuel pressure ranging from 35-47 depending on engine. For a '87 454 it says 34-46PSI.

On yours, was it originally TBI? What year?

THANKS!!!

[Russell]

Most Q-jets won't take more than 5 PSI, all TBI want 15 PSI, and TPI requires 45 PSI.

Just wire the fuel pump to have constant power when the key is set to on, and put on a regulator with a return line headed back to the fuel tank to dump any fuel that isn't needed into the fuel tank again. Cheapest option, and won't need a new fuel pump The Regulator should be set for about 5 PSI or so.

[landpro00]

So, do you ya'll think that the pressure feeding back through the return line could have damaged the switch valve. Not sure, but I imagine the return line would have to run through the switch valve in order to know which tank to return the fuel to.

Don't want to put on a new switch valve until I figure out what caused it to quit, unless it was just age. Just seems like an awful big coincidense though that it would just happen to quit a week after hooking up the new regulator and rehooking up the return line.

I have the Mallory pressure regulator set at about 5.5 PSI as the Edelbrock manual I received with the carb said to set it at.

ANY SUGGESTIONS, IDEAS,DYNAMITE"LOL"?

[crackajacka]

if your block has the provision for a mechanical fuel pump i would swap it over with a edlbrock fuel pump designed for the carb if u had the money for that or just goto the parts store and get one. i find it a lot easyer(and cheaper) to swap mechanical pumps since there right there on the block not in the tank lol.

[bluex]

I doubt he has the provision for a mechanical pump, and if it does and the motor is stock (Otherwise) it would be safe to say there is no lobe on the cam to drive it.

The tanks have a crossover line to help balance them if you overfill one right? I would run a new return line, Y it somewhere and have it dump a little in both tanks. Then you could bypass the switch and not worry about burning it up. Dropping the tanks will be a huge pain and I dont know if they even make a electric pump that makes that low of a pressure. If anything, drop the tanks and take the stock pumps out. Then put the two new ones on the frame somewhere with new filters then if you have anymore problems you wont have to drop the tank to fix the pumps.

[landpro00]

Not sure if it has a crossover pipe or not.

If I run a new return line and split it to go to both tanks at once, won't I have to switch from one tank to another more often and eventually wouldn't the one I'm not using overflow pretty quick. I usually use the same tank for months and then switch to the other one just to keep the gas somewhat fresh.

Does anyone else think the factory line doesn't run through the switch valve like 'Captkaos' stated in his last post? I would think it would have to in order to be redirected back to the tank it came from.

If I decide to install new electric pumps I was going to mount them under the hood somewhere, should I mount them under the truck on the frame rail somewhere instead?

Also, how would I wire them in to the tank select switch on the dash so that it would switch one pump on and the other one off automatically depending on where I set the switch( LEFT or RIGHT). Or would I have to mount like two toggle switches or something for them?

Would I still need to use the switch valve?

How is the factory intank pump set up? Does a pickup line run in to the top of the tank and hang down to the bottom with the pump stuck on the end of it, so that all I would have to do is remove the pump from the end of the line, or what? Or would I have to rig up a new line somehow because removing the pump would make the line already there unusable by the way it is designed.

Sorry for all the questions guys!!! Just want to make sure what my best option is before buying new parts or making repairs.

OH WAIT!, one more while I'm at it. LOL!!!

By the way, does anyone happen to know if the factory installed tuning springs and stuff are correct for the 454 or do I need to buy that tuning kit with additional springs and stuff to set it up correctly? Has anyone else used an Edelbrock 750 CFM Performer carb. on a 454, and if so, what, if any tuning modifications were required?


THANKS AGAIN ALL!!!

[NeCrOmAnCeR]

The return line comming off the TBI or in your case the regulator will not have more than a few pounds of pressure (at most) because there is no restriction in this line. A pump builds up pressure only against a restriction. So no, the switching valve going bad was not due to your setup. The fuel return needs to go through the switching valve so the return fuel goes back into the tank from which it came, other wise two full tanks with a Y-pipe like blueX mentioned would overfill the other tank. Check your selector switch and wiring, then replace the valve with assurance that it was just worn out.

[landpro00]

Well, you just answered a few of my questions before I had a chance to post them. LOL!!! GOOD JOB!!!