R400 Duratec fuel capacity and guage accuracy

[Angus]

On the R400 S3 Duratec I have discovered that when the tank is emptied by the pump (by disconnecting the feed from the fuel rail) there is about six and a half litres of fuel remaining. This appears to be because the fuel pump module, which is mounted vertically, does not reach to the bottom of the tank, made worse because the tank floor slopes forward. The module itself is a cylinder of approx 1 1/2 litres volume. This gives a total of eight litres of dead volume in a tank of about 30 litres, or over 25%. Not good.

 

The fuel pump module is a Ford item here (Ford part number 3M51-9H307 P1697156AT - from a Focus I believe) , and being a moulded plastic unit cannot (easily, if at all) be modified to alter the pickup point. It looks as if the module is designed to sit in a well in the tank floor, which of course is not the Caterham design.

 

I would like to find a way to access this dead fuel to increase the range. Short of a new custom tank and an external pump, has anyone fixed this problem or got any ideas ?

 

I then started looking at the fuel guage on the Stack dash. I have found that it underreads by five litres. Starting from the tank 'empty' but containing the six and a half dead litres, the reading does not climb off zero until five litres have been added. 10 litres actual reads 5, and so on.

 

Alos note that the Caterham Stack is NOT calibratable for fuel. Although the standard stack dash (model 8130) can be calibrated, the unit as fitted as standard by Caterham has this functionality disabled. Stack can reflash the unit to re-enable this and other functionality, for the not trivial sum of £100.

 

Angus

 

 

 

[JimD]

To improve the fuel tank range the pump unit needs to be turned so the pump suction is in the lowest part of the tank. To improve the fuel gauge calibration the float needs to be lowered so at empty it is almost touching the tank floor.

I have the Roadsport SV 175 Duratec 2L built in April this year. Due to a kinked fuel line as supplied by CC (poor quality control), I needed to turn the fuel outlet pipe clockwise from the South West position to remove the kink. This was not possible due to the long arm of the float which points East or towards the centre of the tank.

After some trials my final solution was to bend the float arm down and in a curve around the pump body. The float should be approx 4mm above a flat surface and close to the pump. By doing this the pump unit can be turned so the pump suction lies in the lowest part of the tank, the outlet faces NE and the float rises in the SW corner of the tank. If you are careful with the bending and its rotational positioning when fitted in the tank, the float will just clear the sides of the tank.

I have photos of the mods but am not sure how to get them onto this page, perhaps I can send them to someone to attach to this note.

With the pump suction in the lowest part of the tank you can use all bar about 2 litres of fuel. On two test runs to empty I refilled to the brim with 39 litres and 39.5 litres of the claimed 41 litre tank.

With the floor of the boot removed the tank top and fuel unit are easily accessed. The fuel line is easily removed by pressing in the side tab. I made a tool to unscrew the fuel pump top about 6” diam. I carefully lifted out the fuel pump and for safety covered the opening with my wife’s cooking bowl to stop petrol fumes escaping. The float arm can be removed from the unit by unhooking a plastic tab and pulling out. It is similar to a bicycle spoke and can be bent fairly easily. I used a box to simulate the corner of the tank to check that the vertical movement of the float would not touch the sides. When reinstalling with the fuel line now pointing NE check that it will not be squashed by the boot floor. On my floor the aluminium had already been cut out in this new position as if CC had always intended it to be there.

The fuel pump unit is a very ingenious device; it has its own fuel reservoir which is filled by two methods. (1) Through a non return flap valve when fuel sloshes to the side of the tank when taking right hand corners. (2) By a venture injection pump which uses the excess pressure spill back to jet into a venturi in the base of the pump unit. From this reservoir the fuel is sucked into the pump through a fine cloth type filter.

Note the fuel gauge will be accurate on the straight and level but will read high on RH bends and low on LH bends. My range is about 240 miles to empty and I refill when in the red at about 200 miles.

 

 

Jim

[Tangerine Dream]

I have posted elsewhere but mine is similarly useless. It reads 7/8 when brimmed and has only used about 30 of the 40 litres when reading empty. At Millwoods I asked for it to be rectified under warranty. They found that something (I forget) had been put in 180 degrees wrong at the factory! Anyway, it still reads the same so this is not the problem.

 

One day I may follow the excellent hints above and would also be happy to host the photographs.

 

Otherwise I am going on range: It never does under 28mpg in 'normal' use. This means that 200 miles is leaving a minimum reserve of 7.5 litres. Probably a little pessimistic as the engine is loosening up nicely now.

 

 

 

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R400SV in orange - so far unmodified!

[fred_gustafsson]

Thanks for that Jim. I have the exact same setup and problem. I tried to do what you have done but didn't succeed in my modifications. I will try again now with based on your ideas.

Regarding the pictures, why don't you create an account with the execllent photobox.co.uk, upload the pictures and give us a link to them?