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  1. #1
    desperado's Avatar
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    MSX150 -- next round of mods

    My MSX150 will be running a different ECU for next year. I have gathered all the necessary components to convert the current ME7.4.4 engine management system to a M7.4.4 system.

    The main difference between the 2 system is the fact the M version of the Bosch Motronic ECU utilizes a mechanical throttle body instead of the electronic throttle body used with the ME version. During this past season, I have found the torque and rpm limiter functions/protections of the ME7.4.4 were very difficult to bypass without major changes to ETB operation. A mechanical throttle body will provide the extra flexibility required to manage rpm & boost for higher performance settings. In addition, the M version has a maximum rpm limit of 8,800rpm (fuel cut)instead of the conservative 7,500rpm soft limiter & 7,800rpm hard limiter (timing cut and ETB restriction) of the ME7.4.4.... What's more... the M version uses an LSU4 wideband O2 sensor instead of the narrow band ME version.... and, most importantly, will allow to run up to 19.5psi boost without triggering an overboost error code (while in open loop).

    Anyway... looking forward to an exciting project and gaining significant performance.... will keep you posted & provide pictures.



  2. #2
    Moderator beerdart's Avatar
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    Sounds good will you need different injectors for the higher boost? How about the fuel pressure for the elevated boost? This sounds like a great thing for the MSX.

  3. #3
    ph2ocraft's Avatar
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    I'm curious as to the effect on the lower end of the engine?
    Will he current valve train keep up with the newly found RPM's?

  4. #4
    desperado's Avatar
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    For the injectors, the oem orange injectors will be too small @42lb/hr. I'll go with the injectors that are already tuned for the M7.4.4 and that flow 54lb/h.

    The valve train assembly will be no problem. The snowmobile version operates at 8,200 clutch rpm from the factory. Maximum rpm limiter is set at 8,800 from Polaris on the snowmobile version. I'm running my sled at 8,400-8,500 rpm on a regular basis -- no issue with floating or reliability.

    The main challenge on this project will be the wiring and tuning at mid-range. The M version uses a wideband O2 sensor in closed loop up to about 75% power load... then it switches to open loop. The typical 5,000rpm to 6,500rpm operating range is therefore in closed loop and targeting 14.7:1 AFR...... which could be a little lean for marine application under continuous load. The ME version (oem on the MSX) goes in open loop at these operating rpm's and the engine runs a richer AFR.

    Tuning will be part of the fun.... I guess...

  5. #5
    Moderator beerdart's Avatar
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    Can you use a 1-1 RRFPR??

  6. #6
    desperado's Avatar
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    Quote Originally Posted by beerdart View Post
    Can you use a 1-1 RRFPR??
    No, this is not practical. The ECU has a fuel adaptative function which allows +15% to -15% AFR correction from the base map. Fuel adaptation values are stored into the ECU's memory as an offset to the base map in support to closed loop operation. Altering fuel pressure to correct AFR would only force thew ECU to compensate and "adapt" its base map to achieve lambda (target closed loop value on the M version). If the 15% adaptation range is exceeded, then the ECU would trigger an error code, namely: "maximum adaptation value reached".

  7. #7
    desperado's Avatar
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    I now have access to the MSX150 & MSX110 ECU Eeprom. I will be testing different fuel, timing and boost maps this summer. ECU reflash is possible using a serial protocol via the ECU diagnosis port.

    Below is a download of the MSX110 and the MSX150 boost maps. The blue line is the MSX110 and the red line is the MSX150. You can clearly see at what rpm boost is reduced to derate power and control maximum rpm. Boost reduction is the main strategy used to control maximum rpm.

    .... Unlocking the heart & soul of the MSX 4 stroke, this will be fun...
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  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by desperado View Post
    I now have access to the MSX150 & MSX110 ECU Eeprom. I will be testing different fuel, timing and boost maps this summer. ECU reflash is possible using a serial protocol via the ECU diagnosis port.

    Below is a download of the MSX110 and the MSX150 boost maps. The blue line is the MSX110 and the red line is the MSX150. You can clearly see at what rpm boost is reduced to derate power and control maximum rpm. Boost reduction is the main strategy used to control maximum rpm.

    .... Unlocking the heart & soul of the MSX 4 stroke, this will be fun...
    This is encouraging!

    I have not delved into the Weber engines, but I was under the impression that turbo boost was controlled/limited by a mechanical waste gate. Is the waste gate electronically controlled?

  9. #9
    desperado's Avatar
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    Quote Originally Posted by K447 View Post
    This is encouraging!

    I have not delved into the Weber engines, but I was under the impression that turbo boost was controlled/limited by a mechanical waste gate. Is the waste gate electronically controlled?
    The wastegate is indeed mechanical and the release pressure is 6psi. The pressure flow to the wastegate is electronically controlled. An electronic solenoid controlled by the ECU regulates wastegate input pressure based on the above curves.

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by desperado View Post
    The wastegate is indeed mechanical and the release pressure is 6psi. The pressure flow to the wastegate is electronically controlled.

    An electronic solenoid controlled by the ECU regulates wastegate input pressure based on the above curves.
    Solenoid, as in open or closed, or variable flow/pressure drop, like a valve?

    So the boost (given enough RPM) will always be at least 6PSI above ambient, even with the solenoid/valve open, but when closed the boost can get higher - do I have this correct?

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