Fuel gauge

[simon]

Already posted this on seloc and meant to add it here too but didn't get a chance.

My fuel gauge has started playing up and is now constantly showing full. It's been like that for a couple of weeks but there was one day where it did work but then I wasn't getting any coolant temperature reading (and a subsequent 6k rev limit).
The coolant temp now shows again but it's still showing a full tank of fuel.

Anyone got any suggestions of what to look at?

Hi Simon,

Does your seat belt LED work properly? Cannot remember if the S2 K has them or not - I suppose it does though.

The seat belt switch shares an earth with the fuel level sender, so if both are bust then the earth splice might need refreshing (or more likely you just splice in another earth).

If the level sender connector was open circuit (either because the earth end was floating, or because there is a break in the wire) you would, I think, get full tank indication.

Of course the wiper in the potentiometer in the tank might just no longer be connected to the potentiometer body properly.

You can test that, sort of, if you can gain access to the wires.

Remove the connector, check that the Black wire has continuity to chassis earth or battery -ve terminal.

With the ignition on I would check that you see some sort of voltage in the Green & Black wire (I think that's right - my scan of the manual is hard to read here). I would guess it'll be +5v relative to battery -ve terminal, but it could be higher or lower.

If you're feeling adventurous you can get a potentiometer, connect the wiper to the Green & Black wire and one end or the other to the Black wire and as you turn the pot, the fuel level will change. If it does, that proves the problem is in the tank.

The downside of all this, is that you need to remove the pax seat, the black plastic bulkhead cover behind the seats to gain access to the fuel tank access panel. When you remove the panel, the space inside is restricted, so getting the connector on and off is tough ...

Cheers,
Robin

Robin, thanks for the reply but electrics really isn't my thing and I've no idea what I'm doing so I'll probably get completely lost at some point! Not sure my car has a seat belt LED unless you mean the belt light that shows in the stack display. If the only way to access the fuel tank is by taking the pax seat out then I guess I don't have any choice and may as well make a start to doing that and see what I find.

[robin]

Hi Simon,

Yes, there should be a light on the dash that lights up to warn you that the seat belt hasn't been fastened. If that light works for you (i.e. comes on when ignition is turned on, goes off when seat belt is fastened) then it suggests that the "common" earth fault referenced on SELOC hasn't happened to you.

Removing the pax seat and access panel will not provide enough room to replace the actual fuel level sensor and associated gubbins - you can just about see the connector and the pipes and that's it. To replace the fuel level sensor requires you to take the tank out of the car and then the sensor comes as part of a fuel pump assembly only, I think ... though it's probably possible to DIY refurbish your existing one with some skillz and ingenuity

Cheers,
Robin

[mac]

IIRC the seat belt warning light on earlier S2's are just timed. Certainly on my car there's nothing leading too/from the seat or belt anchor.

I'll try and get a chance to consult the manual tonight

[MacK]

IIRC the seat belt warning light on earlier S2's are just timed. Certainly on my car there's nothing leading too/from the seat or belt anchor.

I'll try and get a chance to consult the manual tonight

Just checked my manual (early S2) and it says the seat belt light is timed (8 secs) but the wiring diagram shows the common earth with the fuel tank sender and the "seatbelt switch".

[simon]

Seat belt light is definitely coming on so either it's not the earthing problem or doesn't share an earth with the fuel tank sender. Anyone know if you can buy the sender on its own or if it has to be bought with a pump? I looked on Eliseparts and it seems they only sell the pump and not the housing and sender.

[mckeann]

Anyone know if you can buy the sender on its own or if it has to be bought with a pump? I looked on Eliseparts and it seems they only sell the pump and not the housing and sender.

Hi Simon,

To replace the fuel level sensor requires you to take the tank out of the car and then the sensor comes as part of a fuel pump assembly only, I think ... though it's probably possible to DIY refurbish your existing one with some skillz and ingenuity

Cheers,
Robin

[robin]

I've never heard of one breaking, so never known whether the part is available by itself - I suggest giving one of the Lotus dealers a call and having a chat with the parts department - or ask Craig at MMC whether he knows the answer ...

Cheers,
Robin

[simon]

Craig at MMC suggested I try disconnecting then reconnecting the battery with the key in and turned on but that didn't do anything so I removed the pax seat last night with the intention of checking the connection to the sensor tonight. However, when I got home from work today I let the car sit and idle until the fan came on and as the temp went up, the fuel level dropped. After it dropped down to the low 90s again I drove off and as the temp dropped further the fuel level went up.

So I think before I start pulling the car to bits I'll order a new temp sender and see if that does anything.

[robin]

Sounds like an earthing issue. Would be well worth checking the battery -ve and the engine earth strap. Also possibly a problem with the stack itself - perhaps it's suffering from a dodgy earth.

Cheers,
Robin

[r10crw]

Simon looks like you will be looking elsewhere but I have a complete pump from my S1 which your welcome to use for testing. Getting it to you wouldnt be too difficult if we can employ the se pony express.

[simon]

Still no idea what's going on with this. I'd done about 120 miles since filling up and the gauge seemed to move a bit and sometimes went as far as half empty but it still wasn't consistently showing the same reading e.g. if I switched the ignition off then on again the reading could change

I went and filled it up tonight and it took about 18 litres so the half tank reading was about right, just wish it would give me the right reading all the time. I'll drive it a bit more and see if the level changes but it's still a mystery!

[robin]

Simon, it's easy to decide which end the problem is - you need a potentiometer (cheap variable resistor) to insert into the circuit in place of the proper level sensor and then twiddle it slowly - the dash should update (probably takes 10s to stabilize on new reading, based on watching the gauge on fast corners on motorways).

If that works, whatever is wrong, is wrong inside the tank. If that doesn't work (i.e. you cannot go from full to empty with a full twiddle of the knob) then whatever is wrong is wrong with the wiring or the instrument display itself.

Another experiment: if you leave the car on the flat, ignition on, engine off, read the fuel gauge (once it hasn't changed for 10s). Now turn on various things in the car - radio, lights, blower motor, crank/start engine, etc. See if there is any change in the fuel level (especially a change that is stable - i.e. it changes from 20L to 25L and stays there).

Cheers,
Robin