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502 mpi guardian issues!!

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  • 502 mpi guardian issues!!

    Good day.

    I have a 99 zx22 donzi with a 454 of throttle body injected motor in it. I wanted to get more out of it so I got a set of big rec port heads, 502 mpi harness/ecu, cam, roller rockers, and all of the other fixins. With diacom hooked up, it shows no knock sensor ever active. The boat is quite doggy coming out of the water and then all of a sudden it just takes right off. But then immediately falls on its face. When you bring the throttle back to idle and start again...it will get up on plane and do it all over again. I was then watching the scan tool closely while driving and it seems like when the boat take off that when it really starts to get timing. And when it falls on its face that's is when it has all the timing taken away. Makes sense...losing 16* timing will do that. I also learned this is basically limp mode.
    Yes timing is good and done in bad timing mode. I have had the thing from one side of the spectrum to the other. Fuel pressure is 43.5psi coolfuel.
    When I key on I get 2 simultaneous codes. Tps voltage high and coolant temp sensor. They can be cleared while driving but just come back with restart. Both sensors are working on the scanner though!
    Please help!

    Thanks

  • #2
    You have a 454 and replaced the heads with 502 heads, and are using the 502 ECM?
    If the ECM has not been reflashed there will be performance issues. The TB injectors may not flow enough fuel, Need to check with Air Fuel Ratio meter

    Tps voltage high and coolant temp sensor. They can be cleared while driving but just come back with restart
    Clearing the codes while running only clears from being displayed but if they are actually still there (sounds like they are) the ECM will retard timing. The MEFI-3 ECM does not have much resolution when it comes to diagnostics. ECT and TPS high can be from an open circuit
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 SeaDoo GTX
    Raw Water Pump Maintenance
    Merc Adults Only
    G-Dad always said "First Liar doesn't stand a chance"

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    • #3
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      Good point from AD above.
      That said. Tps and IAC likely culprits.

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