Successful 318is 55L to 63L Fuel Tank Conversation

[James318is]

Good evening all,

Firstly, thank you to the contributors on this forum who have made my life a lot easier since the purchase of my 318is in September last year. This forum is full of valuable information and as I have begun to clue myself up on the workings of my E30, I think it is now time to re-pay the community by sharing my own experiences too.

Before I ask my questions, like any good forum user, I have made adequate use of the search function, however, the answers I have found are not conclusive in my situation. The threads I have found are very useful and are as follows:

http://www.e30zone.net/modules.php?name ... ats+needed

http://www.e30zone.net/modules.php?name ... der+wiring

http://www.e30zone.net/modules.php?name ... t+facelift

I have tried to replace my rotten 318is fuel tank. Like a moron, I didn't check the physical appearance of the part before purchasing it, instead going off information that suggested the tank must be 63L.

As it turns out, the tank in the car was a 55L capacity, but contains a fuel pump and sender from a 63L unit, preventing the gauge from working.

I have fitted the 63L tank and ordered a second sender unit and understand how to wire the two senders together, but am unsure as to the configuration of the fuel return hosing and also the gauge on the binnacle.

My questions are as follows (especially aimed at those who have successfully performed the conversion):

1) Should the 318is come with standard a 55L tank or did my car contain a replacement part?

2) Where the 55L tank has two metal external pipes, am I correct to add in a secondary hose on the 63L tank running parallel to the metal pipe? If so, what is the stub pipe for on the n/s front of the tank? (The car is currently running so is picking up fuel okay, but I'm not sure if its returning to the second half of the tank correctly).

3) Do I require a gauge binnacle from a late model 320/325 to get the fuel gauge to work with my current configuration?

4) Are there are parts of this swap that I can get away without doing that won't lead to fuel starvation on long corners/roundabouts?

Any diagrams/pictures/replies are greatly appreciated.

Many thanks in advance,

James

[Brianmoooore]

55l tank is standard on an iS.

The return pipe from the fuel pressure regulator on the engine must be connected to the stub on the side of the tank. If you don't do this, you won't be able to access the 20 odd litres of fuel in the left hand tank. If you keep the original fuel pump, then the connection to which the return pipe was connected must be blanked off. This is usually done using a 2" length of fuel hose, a short bolt of appropriate size and a couple of hose clips. There is no pressure in this pipe.

You require the fuel gauge from a car with a 63 litre tank. This is held in place by a single 4mm nut, and is easily swapped over once the cluster is opened up.

The 63 litre tank is less prone to fuel starvation than 55 litre tanks - the fuel can't escape to the LH tank.

[James318is]

Brian, many thanks for your response, it is very useful. I will update once I fit the hoses in the correct configuration and a new gauge.

James

[James318is]

Evening all,

First proper drive out in the car today since the tank swap and the fuel pump is whining (very) loudly - time for a replacement.

After a few miles or so, fuel starvation (complete power drop off) was occurring at around 3k RPM. This issue was magnified when going up hill, and not so bad going down hill or on a level.

I'm sure the pick-up in the tank is adequate (55L pump in a 63L tank) as the depth of the tanks in the right hand side are equal.

Is this lack of pick up due to a worn fuel pump or is it due the fuel pipes being re-routed incorrectly, leading to a vacuum in the system?

For reference, turning the engine off for a brief period seems to 're-set' the problem somewhat.

I will try and sketch up how I have re-routed the pipes. But for those of you that understand, here is a description:

Old return hose for 55L tank > stub on new 63L tank and blanked off at the pump
Thin pipe from filler > into hard line mounted on the new 63L tank
Outlet pipe (coming from the bent pipe on the fuel pump) > new pipe going from fuel pump outlet, routed across the top of the fuel tank into the hose of the n/s of the car

[Brianmoooore]

The only way to check for sure if you have a fuel pressure problem is to hook up a fuel pressure gauge. They can be bought on ebay for £10 or so. Without this test, you are just guessing, but has the fuel filter been changed or known to be clear?

[James318is]

Thanks for the reply Brian,

I do not think the filter will be at fault here but will check as soon as possible. Although I don't want to have the metaphorical blinkers on with regards to the issue, it seems as though a vacuum has been created in the system and that extra load has created the already old and fragile fuel pump to begin to fail (I can hear a very loud whine from the commutators).

I will try and upload a diagram of how I have swapped the hoses to confirm it has been done correctly and try and establish why, if it is the case, a vacuum has been created.

Alternatively, could it be that as the fuel pump is failing, its effectiveness is drastically reduced, and cannot cope with loads after a period of time that it has been running? I struggle to make the direct comparison between turning the engine off to 're-set' the problem and a faulty pump.

Thanks in advance,

James