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Fuel level

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hello everybody.

I´ve been searching in forum about wiring fuel level sender, but I really didn´t find the answer to my concretes questions:

I´m using Link xtremme and I´ve busy all 4 Temp Inputs, so I would have to make an external pull up to an analogue input. However, I´m using AIM PDM08 and I can activate an internal Pull-UP of 2000 Ohm for any analogue input. I would like to know if It would be suitable for my application. Although I have not confirmed It, (I will do), I have read online that fuel level sender is 50 Ohm when empty and about 300 Ohm when full. If we suppose +5V reference on PDM digital input, with 2000 Ohm pull up activated and appliying voltage divisor law, Voltage input would be moving between 0.12-0.65 V. Would this be suitable for application? I also have doubts about using capacitor to control measure fluctuation. Is it really necessary?

My idea would be showing that input info in the TFT Display...

Thank you all.

Attached Files

You will likely have adequate resolution with the 2K pullup although this isn't ideal. I would probably test it with an external pullup in the 500 ohm range. Many sensors only have 8 or 10 descrite outputs (so they are nore fully analog, but return one of 8 or 10 descrite resistances. Handy for cars with digital "chicklet" style fuel gauges.

Exactly what fuel sender are you using, as some increase, others decrease, resistance with the fuel level.

David I wouldn´t like to use an external pull -up if not extrictly necessary, to simplify the wiring install using PDM. However, if you think I should do it, i Will. I´ve read some AIM documents fot Dash Display Inputs (Not PDM Inputs) and for fuel level sender talks about x9 max resistance of the fuel level, so It will show for 5V of reference 0.5V in analog input. I supose 300 Ohm max resistance in my fuel level sender so recomended por dash input would be 2700 Ohm but I would be using 2000 Ohm. Related to descrite outputs, I think my Vag 1.8T a4 b5 fuel level sender is continuous resistance variation.

Answering Gordon, I´m using OEM Audi A4 B5 1997 fuel sender OEN 8D0919673C. I think Its resistance increases when fuel level increases, but I need to go to the garage and measure It with multimeter or going to the junkyard

I attach AIM Dash Fuel level Instructions (NOT PDM Instructions)

Attached Files

Well, just try it.

You could test this on your workbench, by setting up a little test harness, and removing the sensor (or using a potentiometer that can vary over the necessary resistance)

Or just wire you vehicle without the resistor, but make a provision to add a pull up if necessary (ie, bring an un-terminated 5V signal to the connector area for the fuel level sensor, or decide you are going to do this near the PDM connector and leave an extra 5V wire unterminated). Test first using the built-in pullup. Only if needed do you go back an modify the harness.

As for the filtering, I have no experience yet with the aim pdm but assume it has the same analog functions as in the Aim dashes. If you set the analog channel function to >volume>fuel level, it gives you some very long filtering options, so no need to build a lowpass filter with hardware.

Im pretty sure you will still get acceptable resolution with the 2K pull-up. If the sensor grounds through chassis that low voltage range might be a problem.

Okay, thank you guys for tour help. I will use sensor GND, and I Will prepare an external pull Up circuit just un case doesn't works well the 2000ohm pullpup. Thank you!!

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