I have installed an ACCEL DFI system on the 383 in my 67 RS. In order to make it run, there were some mods done to the stock tank. EFI requires a supply and return line as well as a vent line (optional but recommended).

Quick intro for others that might read this thread (experts bear with me):

- The supply line feeds the EFI fuel pump and the pump forces the fuel forward to the engine at upwards of 50 PSI (mine is a Walbro pump and probably makes around 70 PSI).

- The supply line feeds the injector rails and they terminate at the fuel pressure regulator (return type regulator) set for 47 PSI.

- The regulator bypasses fuel back to the tank via the return line. It bypasses fuel such that the pressure in the rails is maintained at 47 PSI

- The return line dumps unused fuel back into the tank.

- The vent line allows air to be drawn into the tank to replace the volume of fuel being consumed in the fuel rails. This helps prevent creating a vacuum lock condition in the tank that might restrict the flow of fuel out of the supply line.

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My setup:
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So, I did all this using the stock tank, and stock fuel sending unit. The stock sender had a single 3/8 steel supply line with a filter sock. I took the sock off the feed line, and 'repurposed' it to be the return line for the EFI setup. I drilled a hole in the sender cap and added an 8AN bulkhead connector to act as the new supply line. I used a length of Aeroquip hose (fuel submersion safe) to dip into the fuel as the new fuel pickup. The supply line is 8AN into a 400 micro pre-filter and then into the supply side of the pump. From the pump forward, the supply line is 6AN.

The return line is 6AN back from the motor, and adapts down to 3/8 hose to connect to the original steel line that is now acting as the return line. So far so good.

Now, the trouble is in the vent line. I tried putting a 'return line adapter' collar in the filler neck that sprouted a 3/8 hose fitting. I connected a 3/8 hose and ran it up under the trunk floor with an inline wire-mesh filter to avoid crap getting in the vent line. The adapter in the filler neck had a little steel 90 fitting that I oriented pointing downward into the tank (to avoid gas entering the vent line when I fill the tank).

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Problem
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I tried this out this weekend, and with a full tank, gas was spewing out the vent line. This was happening not only upon acceleration, but just sitting there. It didn't matter if the vent line was low near where the adapter vent outlet was or well higher (with a longer piece of hose long enough to reach the top of the trunk lid). Somehow pressure was being generated in the tank enough to force fuel out the vent line. I imagine this wouldn't happen if the tank were not so full, but still, that's bad.

So, I swapped the adapter in the filler neck to have the 90 elbow pointing open-end-up. No more spewing fuel while running now, but when I fill it, I get gas on my feet. Also not good.

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Help!
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Can anyone suggest a good strategy for the vent line? I am using the stock RS gas cap. It *is* vented to relieve pressure in the tank but will *not* flow air the other way (into the tank) to relieve pressure from the fuel being removed from the tank (via supply line). I need a solution for both problems

- heat building in the tank causes vapor that needs to be released when not running.
- vaccum inside the tank generated by removing fuel via the supply line (in quantities greater than the amount being returned via the return line).

Some may say I don't need a vent line as I can't possibly draw enough fuel out of the tank fast enough that the old filler neck and cap system can't leak enough air in to compensate. I'm not sure I buy that.

 

Your thinking is bass-ackwards here. The vented gas cap allows air into the tank, not out. If it didn't, even the slowest flowing mechanical system will stop moving from the vacuum inside the tank. One of the reasons the cap doesn't vent out, is to keep the system pressurized so fuel won't siphon back out of the line/fuel pump, giving you a dry start. Try corking off your vent setup and see how that goes.

 

I gotta admit, that sure is the simplest solution!

I gave my (brand new) cap the blow test and I thought it only vented outward, but I'll give it a try capping my vent line.

Thanks!

Mitch