New Walbro 255 in-tank pump installed. Few Questions... - Third Generation F-Body Message Boards

zacharyhorn · 10-14-2009, 01:53 PM

So the other week I dropped the axle and rear suspension and installed my new Walbro 255 fuel pump in place of my stock TBI pump. I am running the Mallory return style regulator with no problems with the stocker. Now, at the lowest setting the regulator goes, it's reading 12-15 psi??? Is this pump to powerful for the regulator?

I am also running the stock 3/8" supply and 5/16" return line. I have heard from a few different people that my return line might be to small? I really don't want or have the cash to buy a new regulator. What are your thoughts on this?

Also, now the pump seems to stay running with the key off??? I'm not sure whats causing this. I have the pump wired to always run when the key comes on. It worked fine with the stocker. I'm really confused and could use some help here.

Thanks in advance.

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remltr · 10-15-2009, 08:54 AM

Shouldn't be. I'm running a Holley 750 DP and the lowest setting is zero(all return). Did you try backing it all the way off,then increasing pressure?

zacharyhorn · 10-15-2009, 09:07 AM

Quote:

Originally Posted by remltr

Shouldn't be. I'm running a Holley 750 DP and the lowest setting is zero(all return). Did you try backing it all the way off,then increasing pressure?

I did. Another thing. Do you increase/decrease the presure using the hex head or the nut? I was using the hex head... I'm thinking it might be the nut that controls the pressure? It's been a few years.

Edit: I'm fairly certain its the allen screw that adjusts the pressure. I think what I'll do when I get home is release the jamb nut and take the nut and allen screw out completely and see if I get zero pressure. Then I'll adjust from there.

Also, Is my 3/8" supply line from the tank enough for my combination?

remltr · 10-15-2009, 08:02 PM

Quote:

Originally Posted by zacharyhorn

I did. Another thing. Do you increase/decrease the presure using the hex head or the nut? I was using the hex head... I'm thinking it might be the nut that controls the pressure? It's been a few years.

Edit: I'm fairly certain its the allen screw that adjusts the pressure. I think what I'll do when I get home is release the jamb nut and take the nut and allen screw out completely and see if I get zero pressure. Then I'll adjust from there.

Also, Is my 3/8" supply line from the tank enough for my combination?

Should be plenty. You just gotta keep the bowls full. I got annoyed with the factory tpi lines and yanked 'em all out. I'm running 6an ss braided supply and return. Out of my reg to carb it jumps to 8an. At idle I run about 5 psi at the carb with no jumping/spiking.

Damon · 10-15-2009, 09:16 PM

Used that exact combination of parts in several vehicles including my current 454SS pickup truck (which has been converted to carb). Always with the stock 3/8 and 5/16" lines plus the Mallory regulator. No pressure creep at all, usually showing only a fraction of a PSI higher than with the stock TBI pump at the same regulator setting.

Wondering if you've got a restriction on the return side somewhere. Maybe something not hooked up right back by the tank when you dropped and reinstalled it.

The center shaft of the regulator (hex head) is the adjustment. Nut is the lock-down for the setting.

zacharyhorn · 10-16-2009, 09:12 AM

Quote:

Originally Posted by Damon

Used that exact combination of parts in several vehicles including my current 454SS pickup truck (which has been converted to carb). Always with the stock 3/8 and 5/16" lines plus the Mallory regulator. No pressure creep at all, usually showing only a fraction of a PSI higher than with the stock TBI pump at the same regulator setting.

Wondering if you've got a restriction on the return side somewhere. Maybe something not hooked up right back by the tank when you dropped and reinstalled it.

The center shaft of the regulator (hex head) is the adjustment. Nut is the lock-down for the setting.

Update:

Well, last night I pulled the hex head screw all the way out and hit the power to the fuel pump. The manual says it should read 0-3 psi. I had 9.5 - 10 psi!!! What gives? I'm almost positive everything is hooked up correctly when I put the tank back in. Both fuel lines are stock up until the regulator. I run dual 6an lines to the carb from the regulator. I had no problems with the stock pump when I was running it. Where would the restriction be???

Also, if I do indeed need to run a new less restictive return line, would 3/8" be enough? Would I have to drop the tank and route the line all the way to the sending unit? I hope this isn't the case...

remltr · 10-16-2009, 09:30 AM

I would pull the regulator apart to see if there is any debris inside that is causing this situation. with that screw all the way out, you shouldn't get any fuel past the regulator,it should be in "by-pass". Or see if you can exchange it for a new one.

zacharyhorn · 10-16-2009, 10:06 AM

Quote:

Originally Posted by remltr

I would pull the regulator apart to see if there is any debris inside that is causing this situation. with that screw all the way out, you shouldn't get any fuel past the regulator,it should be in "by-pass". Or see if you can exchange it for a new one.

I don't think this is causing the problem. Like I stated before the regulator worked great with the stock pump. Now I have the pressure issue. There is a spring in the inside of the regulator though. In the instructions it tells you to pull this out if you run a mallory such n such pump. Can't remember the name off the top of my head. You don't think that maybe my return line can't keep up with the pressure? I do run a decent water filled gauge right off one of the ports on the regulator. And like I said before, with the stocker, it stayed right at 6 psi.

remltr · 10-16-2009, 04:29 PM

Just for giggles, if you have a hose barb fitting or anything to run the return into a gas can off the regulator maybe. I too have a 255, however I run 6an line on both the supply and return sides. I just don't think that there's something wrong with the stock return line but stranger things have happened.

Damon · 10-16-2009, 09:14 PM

Agreed- dump the return side into a jug to help diagnose if it's a return-side restriction.