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2 Fuel Pumps

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fried_guy

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I recently started having what I thought were fuel delivery problems. So I started making big changes to my fuel system. Removed the mechanical pump and put in an electric, changed from rubber hoses to aluminum fuel lines with -AN fittings, added a new bypass regulator, a pre-pump filter, and a post-pump filter.

Turns out the rubber fuel lines before the pump were collapsing from vacuum. :doah:

But I like the electric fuel pump and am going to keep it. It's great when I want to prime the fuel bowls on the carb, and gives me a much steadier fuel pressure (especially when idling).

I dislike the electric fuel pump because it is less dependable (or so is my assumption), and doesn't prime itself well.

The noise/mounting/wiring isn't an issue to me as I can't hear it over my exhaust, it mounted in the frame rail no problem, and wiring was as simple as a 7psi oil-pressure switch and relay (I also added a momentary push button in the cab to temporarily turn on the pump even if the engine wasn't making 7psi- like when it's off).

I was thinking of putting back in my mechanical pump in conjunction with my electric for better dependability and priming. It would be a single line coming from the tank into my pre-pump filter, then split with a tee. One side woud go to my electric pump and the other would have a 1-way fuel check valve and go around the electric pump. Both sides would join back into one after the pump with a tee, go to my mechanical fuel pump, the post-pump filter, return-style regulator, and then carb.

How does this sound? Anyone out there doing something similar? Heard of it?
 
When I was younger my Dad had an electric mounted in the frame, and it ran straight to the mechanical pump. He would use the electric to boost the system when switching tanks, as well as when he would be on steep uphill runs, other than that it was turned off.

Splitting it with a tee sounds like one more failure point, and in a fuel system I would avoid it.
 
I thought of that... but if I decide to turn off the electric pump for some reason... or it dies on me... will it put a restriction on the mechanical?
 
It rarely was run with my Dad's, and I can only remember replacing two fuel pumps in the 15 years he ran it. Never seemed to have any effect on the mechanical pump.
 
Thanks. Good to know. I think I'll slap in the mechanical then and give it a shot some time tomorrow. :D

If it runs like crap then I'll do the bypass thang.

Now I wonder if I have enough -AN fittings to get it all hooked up. :confused:

Any other comments/opinions from anyone?
 
I switched from a mechanical pump to an electric about 7 years ago, I would never do it again.

For some reason, in my not-so-smart youth I decided that the mechanical pump wouldn't flow enough for the 383.

I have since dealt with remounting the electric pump 3 times (changes with suspension, frame, etc), ridiculous noise from the pump and the prospect of a failed fuel pump that I may not be able to find from a local parts store when/if it fails.

I really have been meaning to switch back to an OEM mechanical pump for reliability and silence, it just hasn't happened yet. I keep hoping to switch to propane before I have to deal with any fuel delivery stuff I guess.
 
The electric pump should prime as soon as you turn the ignition on.

One thing to keep in mind is most mechanical pumps run around 7-10 psi. Most electric pumps run 10-15 psi. You may just have to much psi.
 
Yeah, the pump SHOULD prime itself. But I really couldn't conveniently mount it below the tank. My fuel gauge stopped working recently (I shouln't have cut that wire! :doah:) and I ran the tank dry. And it's a PITA to prime that thing after it's dry and above fuel level.

That's why I want to use the mechnical too. And so that I have a reliable backup in case the electric fails in the middle of no where.

The electric pump tops out at 7psi and the mechanical pump tops out at 8.5 psi. I have a return style regulator, so I'm not worried about excessive pressure.

With every mechanical pump I've had, the psi fluctuates wildly... especially at idle. I don't know if it's a major issue, but I'd rather have a steady pressure rating if possible.

Seems to be some conflicting opinions about this... maybe I'll wait for a few more replies before I get my hands dirty today.
 
Running an electric pump AND a mechanical pump inline isn't a good thing as most electric pumps won't allow fuel to flow through them properly should the pump fail and you need to rely on the mechanical pump. You idea about the tee would work but like lectric80 said it is just another possible failure point.

You said the electric pump is mounted in the frame rail but is it mounted next to the fuel tank or up front somewhere? Electric pumps are made to push fuel not suck fuel so this could be your problem depending on where it's mounted. I once mounted an electric pump in the C of the frame rail but it was mounted in the area that was not accessible without dropping the fuel tank to replace it. This was the best location for two reasons, first it was as close to the tank as possible and second it was protected from anything being able to hit the pump. The downside was that i would have to drop the tank in order to replace it. There is nothing wrong with a mechanical pump and they are much more reliable than an electric pump. Most mechanical pumps will produce around 9psi fuel pressure which is more than adequate for a carbed engine but if you have alot of HP you may need more volume.
 
The electric is in the back, but slightly higher than the bottom of the tank, not the top. The 2 times the tank ran dry it's taken a while to prime. Otherwise it works excellent. It's the new Edelbrock quiet flow, good to 600 HP. I have around 450 I would assume.

What I'm doing is replacing the large fuel gauge in the truck with a new tachometer and replacing the small clock with a new fuel gauge. I've already started working on it, but haven't got the new gauges, so the fuel gauge doesn't work right now.

I've always used mechanical pumps in the past, and I've had plenty of SBC engines, and I must say I really like the electric. MUCH easier to set the floats, prime the carb, and a steadier pressure too.

I have a little junk pump and some 3/8" tube that I'll keep in the truck in case it fails.
 
Good idea about the spare electric pump.

My 78 truck has a 454 with Thorley headers and I changed from a mech to elec pump because of vapor lock. I mounted an elec pump (Carter) on the frame next to the tank selector valve, but added a filter between them. Then I ran all new fuel line from there to the carb, but outside the frame, wrapped in foam insulation. The install looks great, and has metal clamps to secure the lines. The original lines ran 1" from the headers!! :eek1: No wonder it vapor locked. Since the install, it's run perfectly.

Anyway, my real reason for posting was to say how reliable the electric pump set up has been, at least for the last 6 months it's been installed. Fuel pressure is 8-9 lbs.
 
Ditto... I pulled my intank pump and put an inline pump mounted to the frame and haven't had any problems with priming or not getting fuel.
 
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