Fuel tank swap - 55l to 63l - quick Q for our Brian M

[jimbom30cab]

Hi Guys, i've got a fuel tank coming to replace the old one on the 318i H reg. I've a feeling it will be the 63l larger tank. I checked out the Wiki and it states i need an second sender, which is cool, but also i need a "fuel return line".

This is where i'm confused as there are 2 fuel lines running from the engine bay to the tank, which connect up at the lower passenger side of the tank. I thought one was the supply and the other the return.

Anyone seen this before ?

Cheers

[Brianmoooore]

You should have three 'fuel' lines underneath your 'H' reg., id everthing is as it left the factory. There should be two fuel lines running all the way together underneath the car, with the brake line, and a third fuel line ( which has inferior rust protection, for some unknown reason) which diverts out to the just inside the sill.
This third pipe is just the vent for the fuel tank, and can be removed back to the rear subframe, as it was on pre facelift cars, with no ill effect.
The other two pipes are fuel feed and return (feed goes to the filter), and with a 55 litre tank, the return follows the feed all the way back to the pump. If you fit a 63l tank, the return pipe MUST be modified to connect to a stub pipe on the lower left front face of the tank, and the redundant pipe on the pump blanked off.
If you leave the return connected to the pump, the LH side of the tank will remain full of fuel.

[jimbom30cab]

fantastic thanks Brian,

yes i removed the vent pipe as it literally fell apart and i've just noticed a little stub connection on the new tank, which from what you said, i assume the return pipe goes onto. I'll then blank off the pump return connection, probably with a bit of hose, bolt in the end with silicon and a nice tight jubilee clip

Thanks again

[jimbom30cab]

Brian, do you know which of these 2 pipes is the return that i need to blank off please?

A or B

Thanks

[Brianmoooore]

B is the one to block. It's just a pipe that goes to the bottom of the tank, and although some petrol would spill out of it as fuel sloshes around in the tank, there's no pressure involved.

[jimbom30cab]

Thanks Mr M

[jimbom30cab]

Just looking at wiring the second sender in parallel with the one by the pump.

the pump sender has 3 wires and the connection to the other sender only has 2 pins

any idea which wires I use on the pump sender
?

thanks

[Brianmoooore]

Senders have to be wired in SERIES. Disconnect the brown/green from the existing sensor, connect it to either pin of the new sensor, then connect the other pin of the new sensor to the pin of the original sensor that you removed the brown/green from.
You will also need the correct fuel gauge for your instrument cluster.

[jimbom30cab]

Got it, thanks Brian