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Does anybody run twin EFi engines with multiple fuel tanks?

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Does anybody run twin EFi engines with multiple fuel tanks?

Old 02-05-2016, 11:47 AM
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Default Does anybody run twin EFi engines with multiple fuel tanks?

Looking to see how others that have twin EFI engines and multiple fuel tanks have their fuel system plumbed. I'm converting to EFI this year and looking for ideas on how to plumb it with my 3 fuel tanks. I have a 155 gal belly tank and two 68 gal saddle tanks.
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Old 02-05-2016, 02:09 PM
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I converted from carbs to EFI on my 42 Harley several years ago. It was definetly a learning process, lots of trial and error. What type of EFI are you using?
I used Merc MPI the first time around, but tuning was a hassle. Now I have Holley HP TBI and love it.

Condensed decription:

It is a closed loop system, using a low pressure pump for lift, feeding a high pressure pump plumbed to the throttle body. The return line is routed through a power steering cooler to the suction side of the high pressure pump. Keeping both pumps
close to the tanks, and as low as possible is key to having a trouble free system.

I have approx 400 hours on the current configuration, with only one minor issue: The Port engine will die at idle occasionally if I let it idle too long after a cold start. I have no idea why. It always restarts, so I haven't put much effort into tracking
down the problem. I use three tanks 290 gallons each and fuel flow meters, so plumbing return lines back to the tanks isn't going to happen.

Steve
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Old 02-06-2016, 10:48 AM
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Walbro makes some great efi high pressure pumps that are impact resistant and low current draw.and relatively cheap for thier output. But the reason for that is because they mount in the tank.
But i am strongly considering it for my dual tank 542 cid jet boat.
Are you set up with mechanical boost pumps? If so i believe enderle and others make oversize check valve assy that make mech/elec combo efi pump systems work better ,plus you can ditch the anti siphon valve and not worry about drainback -cooking a electric pump
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Old 02-06-2016, 11:18 AM
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guessing u have been running the 3 tanks on twin carb motors
so what ur set up now
as commonly u use the 155 tank for both motors inlets
and transfer from saddle tanks to main as main gets lower
with fuel pumps/transfer pumps
I have a main tank and a front mounted ballast tank
use a 12gpm transfer pump to balance boat to water conditions
all motors inlets and returns goes to main
if ur referring to efi return lines to tanks
id run same set up described with return lines tapped into top of main tank
to keep all of fuel in the main tank for boat operation
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Old 02-08-2016, 08:41 PM
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If you are returning the fuel back to the tank (you really should since it's the best way) then you must return fuel to the tank that you are pulling from. Sure, there are some guys that are returning to the filter head, but it may work or it may not. If you return to the tank, then there is no need for a cooler. Mercury returns to the filter head so that they can keep the engine completely self contained. They also have a fuel pump that is just large enough to get the job done,. I'm a firm believer in putting in more pump than I need to have a safety margin. When returning to the filter, you run the risk of vapor lock, air lock, etc. It can make it tough to prime, etc. I just don't like it. If you return to the tank, you will have none of the issues mentioned above....guaranteed. The best way to return to the tank that you are pulling from is to use IMCO's fuel valve. They have a 6 port valve that will return to the tank you are drawing from. It can be switched from the dash and will work multiple gauges. It is a very nice piece, but it's not cheap. This way you can pull from any tank at any time and not have to transfer fuel around.

The other option is to have both engines pull from the main tank and have transfer pumps to move fuel from the saddle tanks to the main tank. That is a little more involved, but it will work.

Here is a link to the switching valve.
http://www.imcomarine.com/cal_store/...uel-valve.html

Eddie
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Old 03-25-2021, 01:50 PM
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Ok going to ask this question again. Hopefully in 5 years more people have converted to EFI and have 3 fuel tanks. How did you do it?
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Old 03-25-2021, 07:54 PM
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It takes 2 imco 6 port fuel valves. In 1 position, each engine pulls from and returns fuel to its own saddle tank. In the other position both engines pull from and return fuel to the main tank. Pretty simple really. I can draw you a diagram if you promise not to laugh at it

Last edited by snapmorgan; 03-25-2021 at 08:02 PM.
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Old 03-25-2021, 08:52 PM
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not sure why it put 4 copies in there
Attached Files
File Type: pdf
Fuel plumbing.pdf (177.0 KB, 109 views)
File Type: pdf
Fuel plumbing.pdf (177.0 KB, 36 views)
File Type: pdf
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File Type: pdf
Fuel plumbing.pdf (177.0 KB, 52 views)
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Old 03-26-2021, 09:23 AM
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I understand where Eddie is coming from and has a great case for returning to tank. But I would plumb to the filter heads and add cooler if necessary. I don't feel failure will be the loss of an engine, maybe a hard start vapor lock scenario. Ease of plumbing and cost affective. You can always add $1500 worth of valves at a later date. Mercury does it and I've seen many 1000HP systems plumbed like that. I also don't feel comfortable cutting into the fill hose and returning there.

I am plumbing to the filter heads on my new Holley EFI builds.
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Old 03-26-2021, 09:44 AM
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I run mine back to the tank and thru a cooler as well. My thought is that either way should be fine with the Holley system.
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