Fuel gauge recalibrator project

[trotty]

Lucky for me I have spares floating around. If u need more picks just holla

 

[Kaldek]

Scratching my head a bit at the moment because my original idea of measuring what's happening with the fuel senders won't work. Since the gauge is a current driven device, this should mean that after the load there would be zero volts that I can read or sample. My brain hurts.

 

[Kaldek]

Just a short update to my plans. At the moment I'm thinking that I will need to cut out the fuel senders from the circuit in the car. I would need to measure fuel levels by creating a voltage divider circuit. Then, using the measured output voltage from my sensing circuit, use a separate circuit with the digitally controlled potentiometer to mimic the behaviour of the fuel senders, but with the resistance controlled in accordance to my calibration table.


The circuit would be similar to the one below, except where this example is measuring voltage at Vout to determine the resistance of a light sensor, we would instead be measuring the resistance of a pair of rheostats in series. I'd draw this in Visio but there's no bloody variable resistor symbol in any of the stencils!

 

[brichman]

I did something very similar to this for the fuel sender in my LPG tank in the sigma. I found out what Its resistance was at empty, 1/4, 1/2, 3/4 and full. Then fit a curve to that data, and used the curve, and the voltage measured over the sender, along with a re-arrangement of a voltage divider to be able to calculate the percentage left in the tank.
This was a bit easier as I was just using an LED matrix as an output, where you're actually trying to get the stock gauge to move.

 

[Kaldek]

I did something very similar to this for the fuel sender in my LPG tank in the sigma. I found out what Its resistance was at empty, 1/4, 1/2, 3/4 and full. Then fit a curve to that data, and used the curve, and the voltage measured over the sender, along with a re-arrangement of a voltage divider to be able to calculate the percentage left in the tank.
This was a bit easier as I was just using an LED matrix as an output, where you're actually trying to get the stock gauge to move.

Cheers mate, what did you use to drive the matrix - an Arduino or just use the voltage directly?

 

[brichman]

Yeah, It was just the voltage directly. It was a 10 'segment' LED matrix, the lights just ran off 5v... Just meant it was simple to drive off the digital outputs

 

[Kaldek]

@TME_Steve what's the best way to drain the tank so I can empty it and start my calibrations by filling it 10 litres at a time?

 

[whats_doing]

Ed,

When we did an e85 tune day @pretzil used an offcut of fuel pump loom with the male plug connected to a jump start pack and some hose to drain it into containers.

However, I had a thought a while ago. Wouldn't it be easier to get the dash reprinted on EL (electo luminescent) and a better designed fuel pump gauge template printed on it as seen here. http://www.ozvr4.com/threads/calibrated-fuel-gauge.14838/

 

[Kaldek]

Wouldn't it be easier to get the dash reprinted on EL (electo luminescent) and a better designed fuel pump gauge template printed on it

Maybe, but it sure isn't my style.

Besides, apart from working out how to do it, I can do all this myself.

 

[pretzil]

When we did an e85 tune day @pretzil used an offcut of fuel pump loom with the male plug connected to a jump start pack and some hose to drain it into containers.

The problem with that was that because the fuel pump pick up is only in one half of the W shaped fuel tank, you can drain 1 full chamber and the other is untouched...
To drain maximum you actually need to drain 1 side almost completely, then drive for a while so the return line fuel siphons more to the pump side.

I only realised this a while after the tune, I actually have NFI what ethanol % I actually got tuned on.

 

[Kaldek]

The problem with that was that because the fuel pump pick up is only in one half of the W shaped fuel tank, you can drain 1 full chamber and the other is untouched...
To drain maximum you actually need to drain 1 side almost completely, then drive for a while so the return line fuel siphons more to the pump side.

That can't be right. The passenger side of the tank only has one hose going to it which appears to be the jet pipe (venturi) hose which pulls fuel across from that side as part of the pump operation via a venturi effect.

 

[pretzil]

As far as I could tell when I pulled the fuel tank out of the spare car, the venturi effect relies on the flow of fuel returning from the engine, not coming out of the pump.

 

[Kaldek]

As far as I could tell when I pulled the fuel tank out of the spare car, the venturi effect relies on the flow of fuel returning from the engine, not coming out of the pump.

Ahhhhhh, good pickup. OK I'll go back to the drawing board.

 

[TME_Steve]

I use an external pump with about a metre of flexible hose to suck it out from the drivers side. Then push the hose over to the other side and suck it out from there. Gets down to a couple of litres. Then because I'm just trying to get high ethanol content i put 10-20 litres of e85 in, then let that mix. Then get it back down to a couple of lies then another 20+ of e85. So as for draining. I don't quite. I just get the 98 down to about 1% which is good enough. Only other way would be to drain by pulling it out. Screw that.

 

[Kaldek]

I use an external pump with about a metre of flexible hose to suck it out from the drivers side. Then push the hose over to the other side and suck it out from there. Gets down to a couple of litres. Then because I'm just trying to get high ethanol content i put 10-20 litres of e85 in, then let that mix. Then get it back down to a couple of lies then another 20+ of e85. So as for draining. I don't quite. I just get the 98 down to about 1% which is good enough. Only other way would be to drain by pulling it out. Screw that.

Thanks mate, figured that's what you did. What do you use for the external pump - something you knocked together using an old in-tank pump or a dedicated purpose built unit?

On the 1% comment, the boys at HPA said something along those lines. That being, the ignition advance benefits of Ethanol drop off after about E70 anyway. It may have even been a bit lower than that but I can't recall the numbers they showed exactly.

Correction: I went back to the info and their actual statements were:

• Most of the benefits of ignition advance are achieved in the lower range of mixture percentages between 98 and E85 (I assume that means up to E50 or so)
• They generally move fully over to the E85 ignition table at around E70 since the blends you end up with from the pump are so inconsistent anyway.
• Therefore their ignition advance tables are built for E70, since the benefits of advancing the ignition from what's possible on E70 are low and it keeps some safety margin in the ignition advance.
• Any deviations in Lambda targets for the 98 and ethanol fuel tables are focused on slightly leaner mixtures for the ethanol fuel table, since the need for a richer mixture to cool the charge is removed

 

[TME_Steve]

Remember that 90% of vr4s now tuning with e85 are running flex so we know what the content is. E7-12 or so would be fine for the 98 end, e70+ would be fine for the 85 end from a fuel perspective although yeah potentially more timing available with 85.

Bosch 044 pump.

 

[Kaldek]

Bosch 044 pump.

Hmm bit exxy for a one off job. Mind you I do tend to tinker a fair bit and could justify it.

What do you reckon about the cheap eBay clones? Since I'm only draining tanks and not worried about pressure.

 

[Kaldek]

Just a quick status update. I haven't ordered an external fuel pump yet, but once I do that I will work on getting a calibration going.

 

[trotty]

I know u are persistent. But in a more effective and much more optioned option would possibly be the utcomp that I've recently installed. It gives all ltrs/100km,instant usage and a bundle of other stuff. But most importantly it's has a fuel gauge in it. Using the injector pulse and scaling it knows exactly how much fuel has been used and fuel remaining in tank to the .5ltr. Fits neatly into the dash clock and looks kinda factory

 

[Kaldek]

View attachment 44092

I know u are persistent. But in a more effective and much more optioned option would possibly be the utcomp that I've recently installed

Oh I'll be fitting one of those too. I do this stuff to take my mind off other things, and to challenge myself. Often the harder it is the more I want to do it, even if it's not a "real" problem.