Another dash2 fuel level question

[rossdagley]

Hi guys

Couple of small issues I'm trying to iron out. Easy one first !

Have the dash2 on it's own. Using the 5v output I've got my (vdo) standard fuel level sender showing 1.7v on the wire (full) and 3.8v (empty). Now - I don't seem to be able to convert that into anything meaningful on the dash. If I put that into the "generate expression from a table) with

X Y
1.7 45
3.8 0

It does give me a formula, but when I apply it it shows like -22.88 on the dash. Am I missing something really obvious?

Cheers!

Oh- and my oil pressure sensor (using a standard RT oil sensor) now doesn't work - any chance its related to using the same 5v feed output from the dash?

Ross

[osborni]

Can you provide more details on how you wired the fuel sender? I do believe that it is a resistance sensor, so you need to follow the instructions in the knowledge base to set it up properly. The amp rating on the 5VDC signal isn't that high, so you may be drawing more than that.

If you set it up right, your reading would suggest that the calibration work isn't right.

[rossdagley]

I'm fairly sure I've got the wiring right - I can measure resistance increases and decreases as I move the sender, and this is converted correctly into a voltage range when the dash is on (and outputting 5v).

I may well have the calibration wrong - that's the bit thats got me confused.

Is it also possible that the oil level sensor (also taking it's feed from the 5v source) is somehow contaminating the reading or vice-versa?

Thanks for your thoughts thus far.

[osborni]

I would take out the formula on the dash and read the voltage directly from the sender. Then re-do the calibration using the Dash as your "voltmeter". It will take out a variable.

Just double check your wires to make sure you don't have a frayed wire someplace.

[Dave E]

I'm using a VDO sender too, basically did as Osborni suggests, stick X=Y in for the calibration and read out the Voltage as you refill the tank from empty.

I don't think only two data points will be enough to give you a decent display - I took a not of the Voltage every 2 litres and used those figures. (It's only a small tank!)

[rossdagley]

Yeah that's what I ended up doing basically - I had an unknown (but quite low) fuel level, so used x=y and left the dash on as I filled the tank in 5 litre increments. After about 35 litres the tank was full , so I converted the voltages into litres in reverse (knowing the end litres to be 45, the siE of the tank) and the equation worked backwards from there.

I'm sure it isn't accurate from 0-15 litres or so, but it's a start! Next time we drop the tank we'll empty it and do the full scale but for now it's enough to get us going!

[osborni]

You will also need to have a longer average setting and a slower rate of change so you don't see the slosh in the tank as you drive.

[rossdagley]

You will also need to have a longer average setting and a slower rate of change so you don't see the slosh in the tank as you drive.

Yep - these are maxxed out already and it's still a bit too sensitive, but liveable

[osborni]

If you have the fuel sensor plugged into a DL1 rather than directly to the Dash, you can also slow down the sample rate to 5 or 10 hz. That way, when you set the "samples to average" to 100 on the Dash, you will get an averaged readout every 10-20 seconds or so. It should slow it down so you average raw data long enough so you don't get brake zone and corner sloshing. (though I see you don't...)

Some foam in the fuel tank would help too.

[rossdagley]

excellent advice. I should pick up my DL1 this week (as soon as Kieren replies to my email :p) so thats a great idea - thanks