Fuel strips. Need to know resistance strip values in ohms

Bendy toy

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Does anyone know know resistance range a fuel strip uses from full to empty? I can't measure mine because (like most fuel strips) its broken. Need to know ohms empty and ohms full measured at the contact terminals located by the fuel pump.

The fuel strip was a nice idea by BMW but badly executed and I refuse to pay for something that will break - quite possibly before e I get home from the dealer. I'm now looking at ways you get a working fuel gauge on my 2008 Hexhead 1200.

The strip works by two copper tracks inside a mylar sheath. One track works as a heater element. The other track is a measurement resistor. The warming effect of the heater alters the resistance. Fuel level affects the temperature on part of the strip so the resistance changes.

I can easily get a 10 ohm to 180 ohm, pole sensor float gauge which I plan to use with a standard dash gauge. It might just work with the OEM dash, but I expect to need a converter box to deliver what the OEM fuel gauge system needs to see. For that to begin, I need to know the resistance range a fuel strip uses from full to empty?
 
Does the fuel sensor output an analog signal directly to one of the BMW control units or does it have a local Canbus interface?
 
Do you know there's a quite amazing (and cheap) fix for a broken fuel strip involving a Piezo Ignition gas/bbq lighter. :D
 
Steptoe said:
Do you know there's a quite amazing (and cheap) fix for a broken fuel strip involving a Piezo Ignition gas/bbq lighter. :D
Click to expand...

Does it involve a claim for the "Fire" part of your insurance?
 
It isn't resistors it is thermistors (temp sensors) so it is voltage output that you are looking for. This won't be right but it will be say 4.5v full and 1.5v empty or the other way round. It could also be in the 3.3v range but definitely not in the 12v range. There must also be some other kind of check as tons of people all over the world have tried to replace it and failed. Something to do with the heater interaction so the controller would see the temp rise and fall and work out the cooling level and therefor the amount of fuel. BMW tried to also retrofit the TC float but couldn't without controller hardware changes so no use for a retro fit.

I am not fully aware of all the inside and outs except it is a lot more complicated than a fuel gauge should be?
 
fatnfast said:
Bendy, get a brew and have a read through this thread on another site. They have come up with a simple way to spoof the bike into thinking it's full and removing the flashing orange light. Although I know your keen on a proper fix, but there is some info on resistance readings etc. HTH.
http://bmwsporttouring.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=770296&page=6
Click to expand...

Hi Steppers
Mine has been zapped but wont zap no more. It's fecked. :(

The AdvRider thread on spoofing the gauge made me think of wiring the pole sender output to the OEM system.

I had not seen this thread - Thanks.

My bike has the fuel strip sensor disconnected and removed from the bike. Its not caused the bike to stop as some have suggested it might. There may be fault error codes but I don't have a 911 to check.
 
I don't see how giving the strip a massive electrostatic discharge is going to fix it - we normally go out of our way to protect electronics against it - however I do have one of these at work to give great big calibrated zaps to stuff :D

http://www.teseq.co.uk/products/NSG-435.php
 
The GS911 gives you realtime outputs including what the fuel strips upto with voltage etc. I don't know if it displays exactly what you're looking for but it might give you some clues to its operation. Next time I refill the tank I'll take a snapshot and do the same when I'm nearly empty and do the same.
 
Engineer said:
I don't see how giving the strip a massive electrostatic discharge is going to fix it - we normally go out of our way to protect electronics against it - however I do have one of these at work to give great big calibrated zaps to stuff :D

http://www.teseq.co.uk/products/NSG-435.php
Click to expand...
One of the failures is the fine tracks break and the pizo trick can sometimes weld them back together. It has been proven to work hundreds if not thousands of times.
 
Marki_GSA said:
One of the failures is the fine tracks break and the pizo trick can sometimes weld them back together. It has been proven to work hundreds if not thousands of times.
Click to expand...

I shall try that experiment with my zapper at work - never seen it done before but I guess the arc across the gap could splatter some bits of copper from the edges of the break and temporarily fill the gap if you are lucky, but at the same time you stand a good chance of killing any other electronic components on the board.
 
Engineer said:
I shall try that experiment with my zapper at work - never seen it done before but I guess the arc across the gap could splatter some bits of copper from the edges of the break and temporarily fill the gap if you are lucky, but at the same time you stand a good chance of killing any other electronic components on the board.
Click to expand...

I don't think there are any electronic components fitted to the fuel strip and should be disconnected from the ECU when zapped.
 
Hi make sure the tank is full and once you remove the two wires from the pump connectors you have isolated it from the ecu.
I have done two other bikes with this fix and never had any issues.
 
Beemerman59 said:
I don't think there are any electronic components fitted to the fuel strip and should be disconnected from the ECU when zapped.
Click to expand...

Don't worry I was only going to experiment with some of the random blank reject circuit boards we have lying around - may be I can work out the optimum voltage v trace width v gap width in order to get the perfect 'splatter' :)
 
AberdeenAngus said:
Thermisters are resistors.
THERMal reslSTORS
They work by changing their resistance with temperature which is what Bendy said.
Click to expand...
I am well aware of that but it isn't resistance that the controller is looking for it is voltage. If Bendy started looking for 33ohm full at battery voltage it wasn't going to work at best and at worst it would have done damage if badly connected.
I don't think it is a constant either hence why the ecu monitors the rise and fall of the temperature to determine where the fuel is at. A hot climate and long running will give a significantly higher fuel temperature than a winters day just started so the resistance will be completely different. The fuel level should be accurate at either condition even although the "resistance" will be different to each scenario.
 
Marki_GSA said:
I am well aware of that .....
Click to expand...

Ok. If you say so. My apologies - it was the words you wrote and the order you put them in that confused me.
Of course the controller is looking for a voltage (or current). You cannot measure resistance directly. It can only be calculated based on the voltage/current response.
I think Bendy understands that.
 
Mark may well have hit on the fundamental flaw in my idea. But saying that the bike has its own temperature sensor and the ECU may software well use that to adjust the fuel strip values as appropriate.

I had a go at chipping the potting resin off the fuel strip connection block. It's like glass so I didn't get very far. However it looks like a small printed circuit board with the wires soldered to one side and the mylar sensing coppers to the other side. Its quite possible there are connecting resistors to limit current to the strip and/or bias the output values.

Im beginning to think a possible failure point is the strips overheating. It would be interesting to know if the owners with repeated failures tend to keep the tank 1/2 empty and do fewer miles rather than brimming it every time and doing more miles (tank spends more time full).

If that is the case a software update could (if not solve the problem) reduce stress on the fine copper conductors.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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