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FMC 688 Getting Edelbrock 35910 Pro-Flo 4 - any tips
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Posted 2021-05-24 8:00 PM (#7735)
Subject: FMC 688 Getting Edelbrock 35910 Pro-Flo 4 - any tips


So I'm in both feet now. While my better half works on painting the interior so I can install the "new stuff", I'm reverting to the motor. I took the plunge and ordered EFI for it. Edelbrock kit. I read on here about someone's experience installing a Holley kit which was probably good background. I've got some other questions though. Since this one sat for 17 years, I'm going to drain and see what's at the bottom of the fuel tank... and clean as necessary before hooking up this new shiny toy.

There is mention of a fuel return line required for EFI. I'm assuming the third leg on the post fuel pump is just that? Or do I have to pull the tank and have it modified. Hope not, and will read the manual of course but wondered if that's the way around dealing with the tank?

Second - I'm hoping I can get in there as is - without once again pulling the radiator out and do the install of the manifold, etc. Thoughts? Tips? Most concern about access... it would be easier if I could get to it from in the bedroom - assuming down through the AC box...and firewall. Looks from the Holley post some coaches have access there. Don't believe 688 has that. Hoping I can get manifold torqued correctly from the sides..

Checking with Edelbrock on what else is needed, coil and type, spark plug wires, regulators, pumps, filters... etc.

Any well wishers - info on your installs will help!
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Posted 2021-05-24 11:03 PM (#7737 - in reply to #7735)
Subject: RE: FMC 688 Getting Edelbrock 35910 Pro-Flo 4 - any tips

Elite Veteran

Location: Victoria, BC. Canada
Sorry, didn't get your name? Maybe missed it from a previous post. Maybe not.

Welcome, regardless!


I just went through a couple of related issues during my - still in progress - Cummins swap.
Turns out the Cummins (maybe most diesels) also have to have a return fuel line for the system to work.

Fortuitously, I'd previously converted my genny to run on propane so I had me a spare fuel line mostly ready to go; however, I also had to clean the tank out in preparation for the new service.

Used my floor jack with a custom wood block/plywood set up to drop the tank. I did it alone. It sucked. Get help.

Putting it back in was worse.

Hooked my pressure-washer to a hot water supply and used an enviro-friendly de-greaser through the machines soap system and blasted the bitch till I was as wet as the inside of the tank. Set it up on saw horses with the large float/sender hole facing downwards so it all drains out easy. Fresh hot water rinse then blast out with compressed air. Then put a small light bulb (the kind that get hot) inside for a day or so to help dry it out. Gave the tank (and the enclosure housing it) a good coat of rust paint before it went back in.

You'll notice when you take the pick-up and sender assembly out that one of the tubes is a bit shorter than the other; the shorter one is the generator fuel-pick up tube. It's designed that way so it will starve the genny out of fuel so it don't suck all gas out of the tank and leave you stranded. According to my mechanic, it (being a little shorter) should not affect its function as a return line in the diesel engine application.

While I had the pick up/sender unit out I reaffixed the float to the rod as it appeared ready to fall off and also did a re-bend correction of the float rod-arm as I determined it was passing too close to the side of the tank for my liking. It seemed like it would get hung-up if I left it where it was.

Make a new gasket for the top seal, too.

Hope this helps.
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Posted 2021-05-24 11:17 PM (#7738 - in reply to #7735)
Subject: Re: FMC 688 Getting Edelbrock 35910 Pro-Flo 4 - any tips


Well - 688 is near full of fuel so I'm thinking of creative ways to drain and give the gas away at the moment. Not sure I'll take it out this round. Might... So if you have to have a return line I'm just not sure how to get that in there. My inline filter has a hose hooked to it. I'll have to trace it to see if it goes back to the tank. Maybe that's so when the electronic fuel pump maxes pressure, there is blow back flow? Not sure as everything is an investigation. Not real clear in the manual. Manual shows two lines from gas tank - 1 to motor, one to gen. Not clear where a return line would come in. Little lost because its new to me and I need to spend more time under there.
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Posted 2021-05-25 11:13 AM (#7742 - in reply to #7735)
Subject: Re: FMC 688 Getting Edelbrock 35910 Pro-Flo 4 - any tips

Elite Veteran

Location: Cottage Grove, OR
My coach had three connections on the fuel tank. One was for the engine, one for the generator and one for the vapor recovery canisters. I removed the canisters and used that connection for the return fuel line. You do need to also use a vented cap for the fuel fill at that point.

This was when I installed an Edelbrock MPI injection system in about 2005. Loved the system.
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Posted 2021-06-09 6:33 AM (#7759 - in reply to #7735)
Subject: Re: FMC 688 Getting Edelbrock 35910 Pro-Flo 4 - any tips


Location: Shoreview, MN
I had to drop my tank too. But for a different reason. When they welded the support angle iron onto the sides of the tank, they stitch welded it which allowed rust to form on the outside of the tank behind the angle iron. I cut off the angle iron and cleaned up the rust. Several holes were found. I took it to a gas tank repair shop and they fixed the holes and applied a coat of tank liner. About $450 to the tank shop. I also shortened the generator sip tube while I was in their. At the rate the 440 burns fuel, I wanted more than the small difference in tube lengths that came from the factory. I don’t remember exactly, but I think it was something like an inch and a half difference to start. Anyway, I agree with the difficulty factor on putting the tank back in. I Shanghai’d my wife to help (she was thrilled as you can imagine).
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