Fuel sensor adjustment/replacement

[Viviacolombia]

Hello,

Doing some work on my 1967 mk1 swb. Took down the fuel tank to remove rust and apply new paint.

The fuel indicator in the dash only goes up to about 3/4 if I fill up the tank completely. It's also quite unreliable when the tank is almost empty.

Are there any more modern/reliable sensors that work with the original fuel indicator?

Or anything I can do to the one that's fitted to increase accuracy?

Some pictures below. Looking forward to hearing some comments/suggestions

Thanks!

[Neil]

that's not a mk 1 fuel tank or sender unit,,,, the sender you have may not be compatable with your dash gauge it will work but not the accurate reading

[DougT]

Judging by the wire arm being twisted and soldered (??) between the float and the sender, that looks like a "bespoke adaptation" of something. I would not be surprised if the float actually bounces on the floor of the tank leading to very odd readings at low level. the float could also jam against the top of the tank before it has reached the full travel of the sender unit.

The sender unit is just a variable resistor with low resistance = full so if you temporarily take the connection from the sender and earth it to the chassis, then you can check that the gauge reads full. You can then connect the sender unit out of the tank and earth the mounting plate of the sender to check if the movement of the float arm gives the correct movement of the gauge between full and empty.

If you get the same odd readings as you do when the gauge is installed than as Neil says, you will need to change the sender unit and adjust that for the non-standard tank. If you get sensible readings with the sender out of the tank then you will need to remake the arm for the height of the tank.

Doug

[Muttley]

I agree, that has a definite “home made” look to it Best to source the correct tank and sender methinks.

[Neil]

yes that's the best route,, uk ebay brings them up sometimes even a genuine sender might be able to be made fit,, ebay uk sell universal fuel gauges with dial separate that work well

[Viviacolombia]

Thanks for all the comments. Will try to make it work as DougT described before looking for a new one.

Another thing I noticed, the outlet for the fuel supply line had a metal pipe connected to it inside the tank. The pipe has an upwards slope which makes me wonder. I would bend it down to the bottom of the tank, but perhaps there's a reason why it was placed that way??

IMG-20180718-WA0002.jpg

Before I lowered the tank I removed some 6 gallons of fuel but the engine was already difficult to start and almost died going downhill due to fuel starvation

[DougT]

Perhaps the pipe had been mounted upside down by a previous owner. How is it fixed to the tank ?

The pipe should try to take fuel from the very bottom of the tank but also trying to avoid sucking up debris from the bottom. Flat bottomed tanks are tricky as you get the starvation problems either going downhill or uphill so your pipe is there to try and minimise the problem by picking up the fuel from the middle of the tank instead of the end.

The standard tank has the fuel pick up as a vertical tube mounted in the same unit as the fuel sender. The sender unit is in about the middle of the tank in front/rear terms and by having a vertical pipe, the end inside the tank can be made to be a few mm off the bottom.

But having a vertical pipe as in the standard tank means that the fuel pump needs to be able to lift fuel out of the tank and to be self priming, meaning that it has to suck air successfully if the tank is completely drained.

Doug

[Viviacolombia]

Perhaps the pipe had been mounted upside down by a previous owner. How is it fixed to the tank ?

Doug

The pipe is soldered to the tank.

I'll try to bend it down to almost the bottom.

[Viviacolombia]

Sort of fixed it. Adjusted the arm of the fuel sensor, indicator goes from slightly below empty to almost full.

Bending the draw pipe down to a few mm above the bottom also helped. Only put a little fuel in and it ran fine.

Not going to change to the original tank as the one I have is 70L and the original is only 40L if I'm not mistaken.

Thanks a lot for the great help!

[Viviacolombia]

Digging out this thread again because I'm wondering what diameter the return line should have?

Mine is quite 'thin' and fuel keeps finding its way out of the carburetor. So I'm getting the feeling there's too much pressure coming in...

[DougT]

I'm a bit puzzled by this.

Depending on the carburettor, but normally if you have a carb set up then you should not need a return line back to the tank. The carb float shuts off the fuel when the float chamber is full and the pump (which is a low pressure unit) has an internal bypass for when that happens.

Fuel pumps for injection systems run at higher pressures (3 to 5 bar) and have a return path so that they can maintain a set pressure to the inlet of the injection metering unit. Or they have a low pressure pump to a swirl pot and then a high pressure pump to the metering unit.

Is it possible that you have a high pressure fuel pump for an injection system feeding a carburettor ? Maybe the V6 was originally an injection engine that has been converted to carb ?

Doug

[Viviacolombia]

Is it possible that you have a high pressure fuel pump for an injection system feeding a carburettor ? Maybe the V6 was originally an injection engine that has been converted to carb ?

Doug

I don't think it was concerted. As far as I found out, the car is an Solex/Pierburg Neus EEIT 38 twin carb. None of the mechanics I've spoken to has seen one like it before which makes me think its pretty rare here.

The return line connects into a thinner tube further down.

I had the fuel pump changed some month ago. Only have attached picture, need to see if I can identify it further.

My set up:

[baconsdozen]

Some carb set ups had a return pipe to the tank as standard to try and stop vaporisation in the fuel lines. Some corsairs with the V4 did,I believe some transits did,and my rover P5b had that system too.
They usually have a narrower pipe on the return side or a restrictor in the line.

[DougT]

Pierburgs were fitted to Cologne V6's so that does make sense. But they still have a needle valve. If the needle valve is not sealing properly due to wear or corrosion then the float chamber will overflow and leak somewhere. They may look OK and seem to seal but don't do so when in use. The return pipe looks OK for size but does it have a restrictor anywhere ?

The pump looks like a "Facet Solid State" pump which is made for a carb set up. It may be branded differently but I would guess it is the same thing. There are 3 differerent flow rates,

Road - 12 gallons per hour 3psi
Fast Road - 18 gallons per hour 5.5 psi
Competition - 25 gallons per hour 7psi

(I think these are US gallons)

Some people work on size of engine so maybe you have the competition pump for a 2.8litre although I suspect that is oversizing it. But it should still work without causing a leak.

If you take a pipe directly from the return connection to a fuel can (or if long enough directly back into the fuel filler) do you still get problems with leakage from the carb. You will probably need to make sure air doesn't bubble back up the return pipe which will then get into the carb by keeping the open end under the level in the can. If you still get leakage at the carb then it is likely to be the needle valve.

Doug

[DougT]

Sorry, didn't read that the return pipe gets thinner lower down, so yes it is restricted. But trying an alternative return to a can etc should let you see if its carb or return pipe

Doug