Fuel Gauge Fix

[benyeats]

Apologies for the longish post, but stick with it.

So I am quite bored today so decided to investigate making a fix for the fuel gauge.

I am at the point where I think I can make a fix that makes the readings a bit more reliable. In order to make the fix applicable to more than just my Mk 1 car I would like some help with calibrating the tank on a number of atoms. The procedure I carried out was as follows.

PART A

i) Wait until car is almost empty of fuel
ii) Put voltmeter across fuel sensor out put and ground
iii)Goto petrol station, ideally at a quiet time
iv) Fill up car recording voltage across the sensor approx every 2 litres dispensed (ignition must be on during fill up, motor does not have to be running).
v) Also record the dash display fuel level at each point (I forgot to do this)

Having done this I now have an idea of the voltage output by the fuel sensor for various fuel levels.

PART B

Next step is to investigate what fuel level the dash displays for various sensor voltage levels, probably can't do this until tommorow when I have borrowed some kit from work.

Using the data from parts A and B I will devise a small circuit which translates the voltages from A into the voltages expected by the dash in B, thus making a reliable gauge.

What would be useful is for more owners to carry out PART A of the procedure and send me the results, this will enable me to make a fix for MK1 and MK2 cars.

It sounds more complicated than it is, an alternative would be for me to carry out PART A next time a nucleus of Atoms meets up and all need to fill up.

Ben

[David Ryan]

Ahhh! Takes me back to my old days as a TVR owner. This involves the customer (having paid 40 or 50 grand) with the privelidge of being the test pilot and fixer of thier own new car!

Why should you have to work this one out. It would seem that this is a well known problem with the Atom and has been for a while. Perhaps they should pay you to sort it out for them, whilst they concentrate on how to get 300 BHP from a 300!

I hate to seem negative, as I am a huge fan of the Atom and will be buying one but as a new club and forum member I have had the chance to go back over the threads on the forum and see the same few silly but annoying issues cropping up. These seem easily fixable if Atom were keen to to it. Rattles, poor headlights, faulty fuel gages and sub quoted BHP.

The Atom is not a cheap car and Simon and the gang are justifiably proud of it but don't seem from what I have read here, to be able to spend the time and money perfecting things, which seems to be contrary to their mission statement.

D.

[Bruce Fielding]

If you've read the threads, David, you'll see that the factory have tried to fix this, but it's proving thornier than one might imagine...

[David Ryan]

How many enthusiastic road miles do you get per tank?

As long as consumption was fairly consistent at say 200 miles on a tank full one would only have to re-set the odometer at each fill to avoid running out of fuel.

[benyeats]

That is exactly the technique that you have to use. (about 120 miles in my case)

However it would be better if it worked as it should, hence I am making a fix.

Ben

[ross.mcw]

I've found that in the Atom 2, 200 miles per tank on the road is reasonable with that dropping to about 100 - 120 on the track.

I don't bother using the fuel guage at all.

Cheers, Ross.

[David Ryan]

Must be bad news to run out half way round the Nurburg Ring! A long and embarrassing walk back to the paddock!

D.

[owi]

Yes, we get a consistent 320 km out of 35L of 98 octane petrol.

[datasafe]

How is the Atom going down under? Is there a great interest in it there?

I'll have to wait until tomorrow to work out what 320Kms is in UK Miles - my brains hurting at the moment.

JC

[John Lloyd]

datasafe said:

my brains hurting at the moment.

Been to work today then?

[atomic]

Ben

If you still need to do this on a MK2 we could have a go on mine now that I'm back off holiday

Nick

[datasafe]

Personally I don't think the solution is going to be as simple as it seems.

I believe most fuel gagues work on the principle of a varying voltage. Obviously (I think) the voltage arriving at the gauge in the Atom is varying a great deal hence the inconsistent readout.

My bet is the problem is in the tank - the sender.

JC

PS John, yes, had to do some work!

[benyeats]

datasafe said:

Personally I don't think the solution is going to be as simple as it seems. I believe most fuel gagues work on the principle of a varying voltage. Obviously (I think) the voltage arriving at the gauge in the Atom is varying a great deal hence the inconsistent readout. My bet is the problem is in the tank - the sender. JC PS John, yes, had to do some work!

I am beginning to agree. The problem in a nutshell is that the sender is not calibrated to the shape of tank so does not give an accurate view of what fuel you have.

What I know from my experimentation is

i) What voltage the sender outputs for various levels (test done whilst filling tank)

ii) What voltage the dash needs to see to display various levels.

So 'all' I need to do is make a simple widget to convert the sender voltage to the correct dash voltage. Cheap microprocessor, bit of rom, bit of ram and we're off.

Ben

[datasafe]

I wonder if you could simulate the circuit design using Electronics Workbench or simular?

Just a thought before going into production - althong the price of silicon is so cheap these days!

JC

[benyeats]

datasafe said:

I wonder if you could simulate the circuit design using Electronics Workbench or simular? Just a thought before going into production - althong the price of silicon is so cheap these days! JC

'production' makes it sound a bit grand. I have a circuit in mind and will get the bits for free by abusing my position and blagging free samples for 'a million selling product development'. I will be making a prototype next week on good old veroboard.

Ben

[atomic]

I suspect that there are 2 factors making the readings unreliable.

The first is the shape of the tank so that the readings from the sensor aren't in direct proportion to the fuel in the tank. It should be possible to get much closer to a true reading using the scheme Ben has got in mind.

The second factor is probably something like "slosh" of the petrol in the tank as the car moves. Unless the tank is filled with some sort of honeycomb structure the fuel level probably moves about quite a bit with the car on the move. This might be harder to fix. At least with the calibration setup it should be possible to get a true reading when the car has stopped and the fuel settled or when running along the flat at a constant speed and direction.

Nick

[Bruce Fielding]

I think that if it was easy the factory would already have done it.

I have a circuit diagram for the Spa dash if that's any use to you, Ben... I'll mail it to you now

[datasafe]

I tend to agree with you Bruce, I don't think the solution is going to be that easy to find.

Maybe there should be a vertical perspex tube standing vertically outside the tank so at least one can see the level of fuel - could be calibrated quite easily too.

JC

[Bruce Fielding]

Well, the handbrake's already operated from the outside, so all we need is a little glass window above the radiator with a temperature gauge and a man with a red flag and bob's your proverbial - 21st century motoring...

[atomic]

You guys don't have much faith in technology do you?