Abarth X1/9 Oil Sender Adapter

Discussion in 'Nuova 500' started by TonyK, Jan 8, 2019.

  1. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    As I have stated the Fiat 500 Abarth engine installed into the Fiat X1/9 is really two entities.

    The issue that presents it's self is that the Abarth engine uses an ECU with 5 volt CAN signals and monitors the wiring of the engine and most of the car. The engine oil pressure switch falls into this problem. Although both the X1/9 and the Abarth engine have a closed pressure switch that opens between 7 and 10 PSI and the signal goes to ground attaching the 12 volt light bulb circuit to the can circuit can and will cause problems. The solution can be resolved in one of two ways. One way would be to use the stock pressure switch to close a double pole 12 volt relay that opens when oil pressure is obtained and breaks the 5 volt CAN bus Signal on one pole and opens the 12 volt dash light circuit on the other pole. A bit of wiring and a relay would have to be added. There is a fair bit of wiring to be done on this car with out this and I wonder how the K20 resolves this similar issue. The other way is to make a TEE fitting that will allow both of the pressure sensors to be installed. As luck has it with this platform space is limited so I made a custom TEE fitting that uses a banjo bolt and allows both pressure switches to be mounted in the oil pressure galley.

    Here is the You Tube Link. This part will be installed on Bob Martin's engine.


    https://youtu.be/7uXW5b-zVgU


    TonyK.

    Grimsby Ontario Canada
     
    lookforjoe and JimD like this.
  2. ng_randolph

    ng_randolph Bjorn H

    Location:
    SF Bay area
    You could do it with a regular single pole relay; Use the stock X1/9 warning light and wiring. Connect the relay coil in parallel with the waring light, and connect the normally open contacts to ground and the Abarth ECU input.

    I think you can get away with something even easier. Connect the oil pressure switch to the stock X1/9 warning light and associated wiring. Connect a diode from the oil pressure switch to the Abarth ECU oil pressure switch input; cathode to the oil pressure switch, anode to the ECU. A 1N4003 or 1N4004 diode works well for this; overkill by electrical reasoning, but mechanically robust.
     
  3. lookforjoe

    lookforjoe True Classic

    Will the diode function properly on the ground side? I was doing some reading on diode use (for an ongoing project) and they indicated that they don't act as a barrier that way. Maybe I misunderstood.

    I would be leery tapping anything into (what is likely) a CANbus circuit, since the slightest irregularity in signal will definitely throw the system out of whack. I rewired my Volvo taillamps to shift which ones operate as brake lights, and although that has no impact on drivability, it sets a strew of error codes in the system. Something like Oil pressure sensing would likely be much more serious.
     
  4. ng_randolph

    ng_randolph Bjorn H

    Location:
    SF Bay area
    CAN bus is somewhat of a red herring in this. The issue is that the various control units do plausibility checks on all sorts of parameters; the fact that this information is typically carried over a CAN bus is incidental. When switching from incandescent bulbs to LED trips a bulb out warning, it us commonly blamed on CAN bus, even though the bus is just the messenger. The real cause is that the lights controller measures the current draw of the bulbs and sets an error if the current is too low. (And if I may digress for a minute, the reason there isn't just a test of "some current" vs. "no current" is that usually multiple bulbs (e.g. both tail lights or both brake lights) are connected to the same channel, so individual bulb currents can't be measured. A single broken bulb (or bulb replaced by LED) results in less current, but not no current).

    The diode circuit I suggested above will result in the input voltage to the ECU being ~0.7V instead of ~0.0V when the oil pressure switch is closed. If the ECU is looking for that type of subtlety it could certainly throw an error code, but I would venture a guess that the oil pressure switch signal is simply read as a "on" or "off" signal.
     
    Last edited: Jan 10, 2019
  5. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    You are correct that the switch is an on/off circuit, but leave it open and it throws a code that the oil sensor wiring is bad. I think the sensor has a residual resistance to it that the ECU is looking for as proof that the circuit is okay. Putting diodes and other voltages on the CAN bus or input does some strange things. I was probing with a 12 volts and hit a terminal, ECU off and the fuel pump started and continued to run key off until I pulled the battery connection for the engine. What I have found messing with this platform is it is better to leave it as close to stock as you can because other things happen that are not expected. Without detailed information on the system of what it is looking for at all times in all parameters expect DTC's to be posted that can and will leave you stranded, with no start or ECU lock out. That is why I installed the TEE and 2 sensors, one for each entity to keep the two systems separate.

    TonyK.

    Grimsby Ontario Canada.
     
    myronx19 likes this.
  6. ng_randolph

    ng_randolph Bjorn H

    Location:
    SF Bay area
    I very much doubt that the system is trying to validate the sensor by residual resistance. In all likelihood the system is expecting the oil pressure switch to be closed before you start the engine and throws a code if that is not the case, as it would be if the sensor is left not connected.

    Also the oil pressure switch is not actually connected the the CAN bus, it is connected to some controller, and that controller is connected to the CAN bus. Anything you do with the oil pressure switch wiring is quite well isolated from the rest of the system.
     
  7. TonyK

    TonyK True Classic

    Location:
    Grimsby Ont Canada
    Apparently you know more about this platform than I do.

    My apologies.

    TonyK.

    Grimsby Ontario Canada.
     

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