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Thread: Vespa GTS - wide-band & tuning

  1. #1
    Carb and Points!
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    Vespa GTS - wide-band & tuning

    First post!

    Backstory: I have a 2007 Vespa GTS, which comes from the factory with fuel injection, electronic ignition, and a Magneti Marelli MIU1 ECU that is similar to other Italian motorcycles. The motor is highly modified, and after searching for a few months for a way to tune the AFR I gave up and bought a piggyback tuner. So that I wasn't tuning blindly, I installed a PLX wide-band, with the sensor in the factory position. The PLX wide-band comes with a converter box that gives a narrow-band 0-1V output that is supposed to be wired into the ECU. The factory narrow-band sensor is a typical 4-wire (grey = ground, black = signal, 2x white = heater circuit).

    Question 1: I have found that I cannot have just the PLX output wired to the ECU, and that the only way for the ECU to be satisfied is if the rest of the of the OEM narrow-band sensor is connected (the grey & white wires). The ECU appears to be checking if the heater circuit is functioning, and will illuminate a CEL if it isn't. Is there a way to simulate a functioning heater circuit to satisfy the ECU? I don't need or want to simulate the signal wire, just the heater circuit side. I don't have the room to mount the sensor in the exhaust, and I would rather not have an open heated sensor in the engine bay (which is under the seat with a plastic gas tank).

    Question 2: Does anyone have any experience with this ECU? I have tried getting a Kess with K-suite 2.47, and FGTech's Gelletto V54, but both were shipped incorrectly from China and ended in a lengthy PayPal battle to get my money back. I have considered a Rexxer, but am unsure if it will allow me to self tune without their proprietary software. One benefit of the Rexxer is that it could turn off the narrow-band sensor completely, meaning I wouldn't need an answer to Question 1. I have looked into MicroSquirt, but the throttle body, ECU, and security system are integrated into one unit, so it's likely I don't have the required pin-outs.

    Thanks in advance for any help.

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  3. #3
    Fuel Injected! steveo's Avatar
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    i do have some experience with vespa injection systems as I used to work for a vespa dealer some time ago

    a piggyback tuner should work fine, lots of people go that way. you should throw the stock o2 back in the stock position, and move the wideband somewhere else

    a temporary hunk of pipe at the exit point will work fine -- you wont need to leave the wideband in there once its tuned. most people dont tune them with a wideband, they just add more fuel till they run properly and go from there

    they'll tune their own cruising afr if you get them in the ballpark so all you have to worry about is heavy throttle fueling

  4. #4
    Carb and Points!
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    Thanks for the help steveo


    Quote Originally Posted by AnnDee4444 View Post
    Question 1: I have found that I cannot have just the PLX output wired to the ECU, and that the only way for the ECU to be satisfied is if the rest of the of the OEM narrow-band sensor is connected (the grey & white wires). The ECU appears to be checking if the heater circuit is functioning, and will illuminate a CEL if it isn't. Is there a way to simulate a functioning heater circuit to satisfy the ECU? I don't need or want to simulate the signal wire, just the heater circuit side. I don't have the room to mount the sensor in the exhaust, and I would rather not have an open heated sensor in the engine bay (which is under the seat with a plastic gas tank).
    I solved question 1: the ECU appears to check for resistance between the two heater-circuit wires. I solved this with a 10 ohm 20W resistor. The heat generated by the resistor is higher than I would like, so I will be switching to a physically larger 50W resistor with a heatsink.


    Question 3: Can Microsquirt use OBD K-line as an input for things like throttle position? The all-in-one nature of the MIU1 ECU means that it will be near impossible to get a voltage signal from the throttle body, at least without opening the case (ECU is physically on the throttle body).

    Question 4: Does anyone know of a way to datalog through OBD K-line?

  5. #5
    Carb and Points!
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    Quote Originally Posted by AnnDee4444 View Post
    I solved question 1: the ECU appears to check for resistance between the two heater-circuit wires. I solved this with a 10 ohm 20W resistor. The heat generated by the resistor is higher than I would like, so I will be switching to a physically larger 50W resistor with a heatsink.
    Slight revision to my first solution: The 10 ohm resistor generated way too much heat. I tested a 20 ohm resistor (actually, two 10 ohm resistors in series), and the heat was cut in half. I will be testing higher resistance to try and minimize the heat output.

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