No announcement yet.

Outputs for fuel computer operation

  • Filter
  • Time
  • Show
Clear All
new posts

  • Outputs for fuel computer operation

    Does anyone have info on what outputs are required from the ECU to make the fuel computer on the dash function?

  • #2
    Asfar as i remcall there's only one wire to be connected to the car underneath the wheel area for fuel cosumption data
    All the rest it's feed trough the cluster connections
    i used this brilliant step to step DIY (credits and thanks to the author) pdf.
    it's in german but cut n paste on googlge translator works just fine my german it's less then zero...



    • #3
      Originally posted by veneto rs2 View Post
      Asfar as i remcall there's only one wire to be connected to the car underneath the wheel area for fuel cosumption data. All the rest it's feed through the cluster connections
      Not sure exactly where you would pick up the signal on a B3/B4 but the fuel consumption signal in a C4 UrS is a blue wire with a black stripe going to Pin T55/31 in the J220 ECU. For the C4, you pick that wire up in Connector Station 2 in the passenger side kick panel. A red T6c connector, pin 5/6: 5/6 Blue/Black (0.5) ECU pin 31 (T55/31- Fuel consumption signal for trip computer - BL/BK Enters the J128 Board Computer at Pin T10a/5 - Note: only used in N.America on 92 spec UrS4s)

      Based on this diagram from, for an RS2 (B4 S2) the wire colour at Pin T55/31 in the J220 ECU is brown/black, which switches to yellow (gold) on pin 3 in a T5 connector on the way to its destination at the J128 trip computer.

      Last edited by UrS4boy; 19th February 2015, 02:01.
      RS2'd 93 UrS4 5 spd sedan
      94 UrS4 V8 6 spd manual avant


      • #4
        Thanks chaps, bit of homework for me there!


        • #5
          There are a number of threads running regarding getting the fuel computer to work with an aftermarket ECU, but given I started this one I will post this here. Mods feel free to move or consolidate. My ECU is a Link G4 Extreme running an otherwise pretty much stock Audi RS2 but the principal should be the same for other ECUs. Anyway, I finally handed over my car to my tuner a couple of days ago and he has got the fuel computer working! I haven't had a chance to calibrate the numbers yet but from brief observation they seem reasonable. I asked my tuner why he went for a non-linear curve and he replied that seemed to be what it wanted. Take that however you like but I would be happy to get feedback from anyone who has experience with this.

          A couple of notes:
          - A PWM output was configured at 10HZ and connected as per 1.12 in the link in post #2
          - The duty cycle of the output PWM signal is inverse to the IDC ie a zero IDC = 100% PWM output
          - If you are testing the fuel computer to see if it's working you will need to have the car's wheels turning as distance travelled is a function of the computer's calculation (MPG or L/100KM) - sorry if this sounds like teaching you to suck eggs but it was something my tuner overlooked the first time he tried to get the fuel computer working

          Here are the relevant screen grabs from my ECU software:

          Edit: attached link not working, use the link in post #2
          Last edited by le mans; 7th March 2018, 09:24.


          • #6
            I noticed a glitch with my set-up. With the ignition on but the engine not running the average fuel consumption displayed on the fuel computer increased up to 51L/100km! The problem seems to be the lack of any pwm output which the computer interprets as maximum consumption. So I've changed the PWM signal activation to 'ignition on' instead of 'rpm>0' and that has fixed it.