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Mercury Promax 220 / Sportjet question

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  • Mercury Promax 220 / Sportjet question

    I purchased a very neglected boat with a Mercury 240 EFI Sportjet. (220 promax powerhead) last year and have completely restored it. It showed almost zero salt water use ( I live and purchased it in Florida). I had to reinstall intake manifold, fuel pump (replaced pump in vapor separator). The engine has compression of 121psi on all cylinders (different gauge showed a little higher).

    I had everything back together and it started great and idled perfectly for miles on the water, however it was covering the plugs with black oil / soot. I converted this engine to premix while I had everything apart and ran it a 50:1.

    After the engine warmed up, I gave it throttle and as soon as the butterfly valves on the manifold opened, it would bog and die unless I closed the throttle back to zero.

    I replaced the trigger as the wires were frayed and made sure the stator was in working order. As mentioned earlier, it starts very fast and will idle nicely (even though the tach is running about 3-4k rpms too high??) The voltage regulators are showing 14.2 at fast idle.

    Just for kicks I unplugged the throttle sensor and the boat would run very rich at idle but it was able to accelerate ( I didn't open it up very much)..The boat now runs with the throttle plates partially open. The TPS disconnected make a immediate difference in allowing the boat to take SOME throttle (smoky but no surging). Also, I cleaned all filters and have 34psi when running. Port side cylinders seem to have a little less soot on them when reading plugs.

    Does anyone have any ideas on why disconnecting the TPS sensor allowed the boat to accelerate ( Tach is running very high for some reason so I don't know how many RPMS I was running at)...

    I purchased a Candoo tool and I’m just starting to play with it..

    Here’s the info from the Scanner. I have tested the ohms on the TPS and it’s a smooth sweep (analog meter). To get the TPS at a .25v reading at idle, I have to install it outside of the holes (see pic). Is this right? It will start with TPS Hooked up and idle lower.. but die quickly.

    WOT on tps is 4.8v.
    Joe
    1997 Baja Boss 232
    496 Stroker BBC / Bravo 1

  • #2
    Joe
    1997 Baja Boss 232
    496 Stroker BBC / Bravo 1

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    • #3
      Fuel pressure too low..needs to be 36psi or higher. Disconnecting TPS riches fuel flow about 30-40% at idle ..I cant remember exactly.
      When in doubt,Trim it out!!!
      Business Owner & Certifed Technician
      Boats I own & use
      20ft Javlin w/250 Junkrude
      17ft Bullet w/200 Merc (SOLD!!)
      13ft Allison w/150 I-6
      17ft Hydra-Sport 175GT
      15ft Allison w/75 Stinger(project)
      14 x 48 Drifter with 1100SS Merc

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      • #4
        I’ll check it again and get the actual psi when running. Any tips for running the motor off a 5 gallon tank to test? Do I connect it to the inlet side of the vapor separator and bypass all the filters? I’m sure I’ll have to add a primer bulb to get it flowing...

        Thanks,
        Joe
        Joe
        1997 Baja Boss 232
        496 Stroker BBC / Bravo 1

        Comment


        • #5
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          IMPORTANT: When checking fuel pressure while engine is running, fuel pressure may fluctuate. Fuel pressure fluctuation (i.e. 34 to 36 psi “234 to 248 kPa”) is common, as the regulated pressure is a differential between fuel rail and manifold vacuum.

          motor should run ok with a "minimium of 34lbs" anything less.. one thing for sure if ya gotta have tha tps where its at in your picture then ya have a big problem with it.. no way it should run with it set like that...….. have you had tha injectors tested and cleaned?

          do you have an oem manual?
          Last edited by Dukedog; January 6th, 2020, 01:17 AM.

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