Working on a weird project and need fuel sender info, eh?

Welcome to the club! I've gone through this so many times on so many projects that I decided to stop googling it, looking on rockauto, and digging through factory service manuals every single time and record this info here, mostly for my own use, but if it's of use to you too, great.

Fair warning, this information is partially based off what I found elsewhere on the internet. Some is from my own measurements. Some is from factory service manuals. NONE of it should be absolutely relied on; I make no express warranty that this information is accurate in any way. You should verify it BEFORE fabricating or ordering expensive components that depend on its accuracy.

Expect the quality of this information as well as the range and depth of the data to grow as I find it. Also, feel free to contact me with info you would like added to this page and I'll get to it as soon as I can. My email is kastein @ W1KAS dot net. Please provide as much information as you can, but without offering more confidence than you have, and I'll try and find info to confirm and improve on what you gave, rather than trying to correct a year or model specification that is more precise (and wrong) than reality.

Basics (first number is empty, second is full):

  • GM up to 1964: 0-30 ohm
  • GM 1965-1997: 0-90 ohm
  • GM 1998-up: 40-250 ohm
  • Ford up to 1986: 73-10 ohm
  • Ford 1987-up: 16-158 ohm
  • Mopar up to 1986: 73-10 ohm
  • AMC 1950-1977: 73-10 ohm
  • VDO: 10-180 ohm
  • Steward Wagner/Sun/Omega/Autometer/Classic Instruments (ex. OE vehicle specific units): 240-33 ohm
  • Dolphin: 0-90 ohm
  • Jeep (XJ, MJ, YJ, SJ) 80s-90: 1-88 ohm (44 = half tank) - note: 1-88 ohm is listed as late as '95 in the YJ FSM. I have not verified if this is true or if YJ switched to 105-5 ohm like the XJ/MJ did in 91 or in 93 when the gauge cluster changed due to the speedometer no longer being cable driven.
  • Jeep (XJ, MJ, possibly others) 91-95: 105-5 ohm (33 = half tank)
  • Jeep (XJ, possibly others) 96: 105-5 ohm (33 = half tank, this is one of two fuel level sensors in one unit)
        - SECOND SENSOR STRIP: wired to ECU on C165 pin C26. There is no documentation in the FSM concerning the second sensor strips resistance specifications. I have personally measured an OEM sending unit and determined that this strip reads 100 ohms +/- 5% at full tank and 1100 ohms +/- 5% at empty tank.
  • Jeep (XJ, likely others such as TJ, late ZJ, WJ) 97-01: 270-20 ohm

    Notes:

  • GM 60s-90s and Jeep 90- are close enough to likely "just work". Linearity is not guaranteed.
  • Chrysler JTEC ECUs employ an interesting constant-current circuit in their fuel level input. It uses an adjustable LM317 voltage regulator with a 39.2 ohm resistor O-A and the level sending unit resistance A-ground. There is also a protection diode and polyfuse from the sender input to a supply rail to clamp the input to a survivable voltage even if it is shorted to 12V.
  • GM P01/P59 ECUs for use with the 40-250 ohm sending unit appear to use a 250 ohm resistor from the sending unit ADC input to 5V AVref and the sending unit resistance from ADC input to ground. As such the practical range limit is about 0.8-2.5V at the ADC. If you are calibrating your own ECU via hptuners, tunerpro, etc you SHOULD be able to use most of the above senders with these ECUs, just be aware that the lower the resistance range of the sender is, the higher the current flow through the pullup resistor will be at empty and also, the lower your resolution will be. For example, with a 0-90 ohm sender on an ECU of this type you will be limited to about 0-1.33V range at the ADC input, which is only about 68 ADC counts. Not ideal. But VDO, aftermarket Wagner/Sun/Omega, and some Jeep senders should be easy to get an acceptable calibration out of.

    references:

  • NAXJA thread post
  • HAMB thread
  • Another HAMB thread
  • 1989 Jeep Factory Service Manual (my personal copy)
  • 1996 Jeep Factory Service Manual (my personal copy)
  • 1997 Jeep Factory Service Manual (from XJJeeps.com reference document archive)