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  1. #1
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    2003 Mercury 250EFI won't go above 2k RPMs.

    So the story is I went to take the boat out and I'm only running 2000 RPMs Max but as it goes on it sounds as if I'm running out of fuel. I have checked everything as far as the basics. All fuel pressure is in spec. The ignition is inspect no field coils brand new plugs. I even replace the high pressure fuel pump thinking it was that due to the symptoms as well as the low pressure diaphragm pump. But as said fuel pressure is inspect so it doesn't seem to be that. Also fuel injectors were pulled and flow tested and that was brand new. Compression is 130 across the board. Really stumped at this point seems almost electrical related. TPS map sensor spark plug wires are all almost brand new. Anyone have any ideas?

    The day before I took the boat out I changed batteries to new batteries and I change the propeller from a 27 to a 24 pitch due to feeling like I had a lot of prop slip. I tested the batteries with the legitimate battery tester and they tested okay. I'm almost left with nothing to do but put the original prop back on and the old batteries and just see what happened since that's all that was changed.

  2. #2
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    Did u try the primer bulb?

  3. #3
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    Well the bulb stays firm and it isn't too old, also fuel pressure was tested with gauge throughout the rev range in the water. Stayed within spec.
    Last edited by LIGlastron; 06-06-2020 at 03:38 PM. Reason: Written 2x

  4. #4
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    Quote Originally Posted by Merc 2.5 View Post
    Did u try the primer bulb?
    Well the bulb stays firm and it isn't too old, also fuel pressure was tested with gauge throughout the rev range in the water. Stayed within spec.

  5. #5
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    Could be the high side of the stator dropping out....
    "One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors". Plato .

  6. #6
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    Quote Originally Posted by flabum1017 View Post
    Could be the high side of the stator dropping out....
    I was told this engine has a trigger and no stator could that be correct?

  7. #7
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    Just to say what was addressed. New spark plug wires,new spark plugs, new high pressure fuel pump, rebuilt the low pressure diaphragm fuel pump, check all coils for a spark during load test in the water all checked okay. Fuel pressure checked okay throughout the range even when starting to bog and at 2K RPMs. TPS seem to check okay. .38 at idle, and 4.96 at wide open. Anyone have any input? this point you could tell I'm just pretty much throwing parts at this thing. Do TPS and map sensor rigzone about 2 months ago and boat was running great after. seem to change the two batteries to a GM's and change the prop and now this is my problem

  8. #8
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    Quote Originally Posted by LIGlastron View Post
    I was told this engine has a trigger and no stator could that be correct?

    Oops, you're right.

    I assume you have checked for good spark on all cylinders?
    "One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors". Plato .

  9. #9
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    Is your alarm working? does it beep when you turn your key on?
    "One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors". Plato .

  10. #10
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    Quote Originally Posted by flabum1017 View Post
    Is your alarm working? does it beep when you turn your key on?
    good spark on all cylinders with checked with diagnostics on the water we went through all the basics nothing seems to be wrong. I am getting a single beep when I start the key. One thing I did notice the last time when I was acting up was for a short time I was getting one long beep followed by one short additional beep but then it just stopped happening so I'm not sure what that was about. Since then it's been doing the normal one beep per start and diagnostically everything seems okay

  11. #11
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    What plugs ? Should be QL77CC champions . Believe that motor has a stator . It also has a key way between the flywheel and crankshaft . Make sure it hasn’t sheared . Hf...

  12. #12
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    Quote Originally Posted by half fast View Post
    What plugs ? Should be QL77CC champions . Believe that motor has a stator . It also has a key way between the flywheel and crankshaft . Make sure it hasnít sheared . Hf...
    Yes I'm running QLC77Ács at .035 .

    I'll read into the stator more, been going through all possible options.

    As far as the keyway wouldn't that make it rev up uncontrollably? Is the only way of inspection on that looking behind the Reed cages?

  13. #13
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    If you have the single ecm on the side you dont have a stator.

    Sounding like your going into limp.

    The alarm should be sounding though.

    I just had this happen to my 3 liter last weekend, port temp sensor went bad.

    It could be alot of other things though. A computer would help.

  14. #14
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    Quote Originally Posted by RSWORDS View Post
    If you have the single ecm on the side you dont have a stator.

    Sounding like your going into limp.

    The alarm should be sounding though.

    I just had this happen to my 3 liter last weekend, port temp sensor went bad.

    It could be alot of other things though. A computer would help.
    I went to a Mercury repair shop yesterday as a last resort after throwing way too many parts and money at the thing. Of course he didn't find the problem however it gave me more confidence in the motors health. we did both bench test and water tests with the diagnostic equipment hooked up to the engine:

    -Great compression, 130 straight across the board cold engine.

    -Ignition system all working properly even with load. he dropped off one cylinder at a time with the DDT.

    -Good fuel pressure at idle and under full throttle pressure is not dropping off when issue is occurring

    -Removed injectors yesterday and bench tested them. The spray throughout all 6 looked brand new. Perfect flow.

    -Reed valves and cages all perfect

    -Voltages seem good.

    -TPS seem to check okay. .38 at idle, and 4.96 at wide open

    He checked everything that he could with his knowledge of two stroke efi engines. He was a very thourough tech and went further than expected with it. He deals with more for strokes nowadays. However he hooked up diagnostics to the motor no codes, no warning lights. It does have the single ECM. Would the temp sensors throw codes? I have a certified Merc manual for my engine so I know how to test those sensors. What about weak oil pump, would that restrict me to 2k? Wouldn't there be warning sounds? What can I possibly look for that could keep guardian system from activating ?

    Could it be the ECM? Really the only sensors that haven't been changed practically are crank position sensor, temp sensors, thermostats, and poppet valve.


    There's very little left on this engine that's old after all the parts I've thrown at it. At least I'll know most of the parts on it are new ��
    Last edited by LIGlastron; 06-07-2020 at 07:49 AM.

  15. #15
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    If temp sensor is bad it will read cold and pour the fuel to it I believe, b worth testing if u can

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