Fuel won't siphon from tank

[Voltron]

I've got a 7M-GE swapped into an MX12 Corona.

For fuel, I have a Bosch EFI pump under the car, and below the tank. Just a hose running from the stock hard line that comes out the top of the tank into the pump.

My issue is that I can't get fuel to flow out of the tank, kickstarting the siphon effect that will keep the pump fed with fuel.

Is there a trick? I've tried sucking on the fuel hose, and was rewarded with a face full of gasoline, but no steady flow.

Thanks for any help.

P.s. just less than 2 gallons ( about 7.5 liters ) of fuel in the tank. That matter?

[RA35GT]

Bosch efi roller cell pumps generally don't like sucking (self priming). I.e. they need the inlet to be covered in fuel at all times.

Even if you get the fuel siphoned the first time as soon as you key off the pipe from the top of the tank down might drain and you will need to prime it again.

Options are to install a lift pump/surge tank setup.
or
Get a fitting installed on the bottom of the tank
or
Install an intank fuel pump
or
if you're lucky you might be able to find a factory efi car with a fuel tank/system which fits into your car.

[ToyTA22]

As RA35GT said bosch pumps need positive head of fuel, best bet is use high volume in tank or inline pump to feed bosch pump preferably with surge tank in between but not totally necessary.

[Voltron]

As RA35GT said bosch pumps need positive head of fuel, best bet is use high volume in tank or inline pump to feed bosch pump preferably with surge tank in between but not totally necessary.

Thanks guy for the replies.

My initial setup was with a lift pump into a surge tank then out to the EFI pump. Work great, but too much fuel. Couldn't get the fuel pressure low enough. Also, several people said that was overkill for a stock 7M-GE. The thought was that once the siphon effect got started, I wouldn't need all that kit. So I scrapped it all for just the EFI pump under the car.

I was hoping there was some trick to get the fuel flow started. If not, then I'll pull the tank and have a fitting welded to the bottom.

Thanks all for the advice.

[RA35GT]

Assuming you are using the same efi pump from when you had the surge tank, it will still be too big without the surge tank...(Assuming you can keep fuel up to it)

If you can't get the fuel pressure low enough make sure there aren't any restrictions in the fuel regulator and the return line itself. (As well as making sure the regulator is ok too)

If that all checks out, you might have to get a smaller fuel pump.

[George]

What do you mean by "too much fuel"? How did you determine that?
If it's too much pressure, check your return line as suggested above. Or run your pump with a resistor.

Also try to open gas filler cap. Maybe it's tank vacuum that prevents fuel from siphoning. Normally, the effect must be self sustained as you supposed.

[Voltron]

What do you mean by "too much fuel"? How did you determine that?
If it's too much pressure, check your return line as suggested above. Or run your pump with a resistor.

Also try to open gas filler cap. Maybe it's tank vacuum that prevents fuel from siphoning. Normally, the effect must be self sustained as you supposed.

I had a a fuel pressure gauge plugged in and read ~45psi if I recall corectly. Maybe the EFI pump was straining to push against the few PSI in the surge tank? Now that I think of it, that seems far-fetched.

The Bosch I have is just some OEM part for a euro car. I think the part number correlated to a Volkswagon vanagon or something.

Thanks for the advice guys, I'll try running the pump with the gas cap off

[RA35GT]

Theoretically there shouldn't be any pressure buildup in the surge tank.

The top of the surge tank should have a return to the top of the fuel tank.

How was your fuel system plumbed up?

[Voltron]

This is the setup I had previously:



Stock return line too small for EFI?

[RA35GT]

That in principle looks ok.

I have seen on one car where the stock return line was too small.

Easiest way to check if it's the return line is to plumb it into a bucket off the regulator and see if it changes the pressure.

[Voltron]

Thanks so much for all the help!

I pulled the gas tank out and brought it to a shop to have a fitting welded onto the bottom. That should solve my fuel feed issues once and for all.

I've also seen situations where the stock return line on a previously carb'd car is too small for EFI. Once I get the tank back I'll test again. If there is still an issue, I'll drain into a bucket off the return like you advise.

Thanks again

[crowncustom]

I have done the same conversion in a MX13 and all I ran was a MX62 Cressida EFI pump using all the factory fuel lines with no issue at all.Doing the same with my MX22 as well but this has a 5MGE and the fuel pressure figure you posted sounds about right for an EFI set up.
Cheers Brett.

[Voltron]

Here is my solution to all my fuel problems:





Took the gas tank to Performance Options in Oakland, and had them weld a steel bung to the bottom. Now my under-car Bosch fuel pump is gravity fed fuel and we're done. Should have just done this in the first place! So easy.

Haven't checked the fuel pressure yet, but the car is running. Even if roughly, it's running!

Edit: I don't know why the botom photo is upside down