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  1. #16
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    So the problem came back this year in July and seems to be occurring more frequently and at lower temperatures and rpm ranges. Engine performs fine for the first 5 to 30 minutes and then intermittent surging in RPMs in the 3000 to 4000 range and 4000 to 5200 range. After doing some more research this surges could be related to a failing low pressure fuel pump that either fails to supply the highpressure pump with enough flow or the high pressure pump begins to pull fuel through the vent in the VST if the low pressure pump stops functioning. I feel as if the intermittent surges are moments of lost pressure when the highpressure pump is momentarily fuel starved.
    The low pressure pump is supposed to have an AMP draw of 1 to 2 amps and mercury says to replace pump if above 2 amps. Last night at the dock i used a clamp style amp meter and depening on wire location in the clamp i got .4amps to 1.9amps at first. after 10 minutes of idling i got a range of 1.4 amps to 2.9 amps. I don't understand the mechanism yet how increasing amp draw in an electric fuel pump can eventually lead to it no providing proper flow or pressure.
    In addition i also have a symptom that i have read is related to a failing low pressure fuel pump where if i trim the motor i get a drop in rpm while trimming.

    Friday will either hookup a fuel pressure gauge to see if im getting pressure drops when surging occurs at speed or Ill replace the pump and see if all these issues go away.

    Lastly engine was making a banging sound i could clearly hear at idle turns out the aft mount bolt on the alternator is lose and banging and hand pressure stops the noise and shake. Debating on just retorquing to spec or wondering if i need to replace any of the rubber mounts in that area.

  2. #17
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    The trim issue is amp draw related, look for a rubbed or bad wire from engine to trim switch (if the engine mounted one doesn’t drop rpm but cockpit switch does)

    amp draw means the electric motor is struggling (capacitor or brush is shot maybe busted winding)

    torque the alternator mount the vibration can bugger it up a little.

    If something like that that you could have a electrical power Issue. Watch the voltage meter next time it happens, if the voltage drops like when you hit the trim you have a wire killing the electrical system.

  3. #18
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    http://www.bbcboards.net/showthread.php?t=403893

    I didnt go through the wiring diagram to understand how the pump draw can be related to trim draw but this guy seemed to be well document that the Low pressure pump was the culprit after chasing after more obvious causes like you are suggesting. Of course anyone can be mistaken. Lots of things seem to point to my low pressure pump begins to heat up draw excessive amps which I don't understand yet but eventually it leads to starving or a pressure drop in the highpressure pump.
    I agree i think heat maybe comping from brushes and resitance and amps creep up but i don't yet understand how this eventually could lead to momentary surges in fuel pressure. is there a relay in the low pressure pump that can surge on and off with high heat or does the resistance get so high at temps that it stops turning? idk
    Last edited by Fishinmymission; 10-02-2019 at 12:21 PM.

  4. #19
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    I read thread 17 motive and i thought you were chasing possible fuel pump low to high delivery not the trim pump . I had also read on here about the coils but thought I was reading earlier opti - had coil issues . Then again 900 hrs could be either . Plus injectors . I believe fuel could be a culprit - especially not showing code . Not sure and not professing to be a tech at all . I too would be checking fuel pressure but you need a hookup on the shrader valve and a T in I read here . Hopefully some One chimes in on procedure for us all to learn . Interesting thread - i will open the book and read the topic -

  5. #20
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    I have smart craft vessel view mobile and don't get any codes(besides the non related ones i blocked 3 years ago that apply to four stroke engines etc). Warning alarm works and no alarms. I will keep you guys updated

  6. #21
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    Quote Originally Posted by kellytheaker View Post
    I read thread 17 motive and i thought you were chasing possible fuel pump low to high delivery not the trim pump . I had also read on here about the coils but thought I was reading earlier opti - had coil issues . Then again 900 hrs could be either . Plus injectors . I believe fuel could be a culprit - especially not showing code . Not sure and not professing to be a tech at all . I too would be checking fuel pressure but you need a hookup on the shrader valve and a T in I read here . Hopefully some One chimes in on procedure for us all to learn . Interesting thread - i will open the book and read the topic -
    Procedure wise its pretty easy I'm just lazy and want to do as little work as possible diagnosing. I'm having a long hose with gauge made so i can watch pressures coming out of fuel rail while the surging is happening. If I see surging i know the issue is somwhere between my fuel tank the high pressure pump output. I could T into after the low pressure pump to make sure that its not giving the 6 to 9 PSI as specced but I think i have enough evidence to just replace the the Low pressure pump and see if the surging goes away. already bought the new low pressure pump assembly with new hoses and hoseclamps for 52 bucks and next day delivery on amazon.

  7. #22
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    Get back on your findings of fuel pressure - high and low readings - i believe the compressor also needs a difference met with pressure . I' relatively new to these optis and look forward to your findings . A-Scan may be helpfull and may show the culprit . And or a good tech guy

  8. #23
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    on optimax 2.5L(dif pressures for pro-xs and xs engines) air pressure side is regulated to be 80 PSI higher than atmosphere, regulator vents off excess air to maintain 80 PSI. The fuel regulator opens up at 10 psi higher than whatever the air pressure is and returns excess fuel back into the engines fuel system so it maintains 10 psi greater than air side. So as long as the high pressure pump can make over 90 PSI everything works. If the high pressure fuel pump is making less than 88 PSI the fuel flow wont be properly set up. And if the pressure drops below 80 PSI it literally cant push fuel into the air injectors as the air side will leak into the fuel side(fuel cant flow into a higher pressure cavity). thinking is if the high pressure pump get momentarily starved from down stream pumps not providing the correct fuel flow pressure drops could be causing surges in RPM. Will be doing the work tomorrow on my day off.

  9. #24
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    your smartcraft should show a low side pressure reading on it if programmed correctly to show it. Mine does and shows 10 psi all the time. U
    You also could be having fuel pressure reg issues and tracker valve issues. Gauges on the rails would show that.
    Last edited by XstreamVking; 10-03-2019 at 09:24 AM.

    83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
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  10. #25
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    There is only a fuel level sensor that Smartcraft vessel view mobile picked as an error up when I contacted mercury about it two years ago they said this would not apply to me setup as I did not have a fuel level sensor in my boat so i blocked it. Maybe they were wrong and this is fuel level somewhere in the motor?
    I know i have water pressure but i have not been able to see a fuel pressure through the app yet. Also any idea where the fuel pressure sensor is located? I just looked through the 2001 optimax 2.5L wiring diagram and there does not appear to be any fuel pressure sensors. Of course my engine is a 2006 so not sure if they added one.
    Last edited by Fishinmymission; 10-03-2019 at 10:46 AM.

  11. #26
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    When I read the manual - it showed fuel pressure was checked with guages and i have not hooked up my DDT - to see if it shows data like that . All I know it was guages that were discussed and tee off of one . Good point Xtreme - if you can see it on SC - i think his would as well . From the reading of threads here - i have only read that the pumps can stick when sat and i know personally of one but it was a 200xs .That doesn' sound like same issue - your running . Sure could use an opti tech to jump on this and talk about problems they are seeing for frequency and possibly send you on a solid item to check .

  12. #27
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    The shrader on the vst is for low pressure pump

    i was just suggesting an order of fixing stuff. If what is dropping rpm when you activate trim is a lose wire or wire that’s bare; it is possible it can draw power even when the trim switch isn’t active.

    In no no way does it preclude the low pressure pump from being faulty.

    It simply point to a common condition of rpm drop from some form of electrical draw. (The loose alternator also made me think of the exciter wire problem some had where it was loose and prevented the output from increased under load)

    opti are a mess of problems to diagnose diagnose as many systems produce the same issue.

    For instance you could have the pulse pump starving the vst and causing the low pump to runs wild.

    Thats not not a bad idea ( prime the vst and drain it in a bottle mark it. Next time it acts up shut down and test the bulb see if it’s tite. If not drain the vst and see how low it is.)

    you can skip the trim issue issue if you want. Was just saying the results of the issue were the same.
    '06 Tracker All-Fish/Tournament V-18 90 Optimax, 46.8 gps Goal one complete reach 45 mph.

  13. #28
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    So I hooked up the pressure gauge to the fuel rail. There was not a drop in fuel pressure when the engine started surging but there was def a slight flutter in the gauge needle every time the engine surged. Consistent but slight enough to not definitely be any certain thing. Could still possibly be ignition coils and the drop in compressor speed causes the flutter. Low pressure pump was cool to the touch no signs of over heating. Different style clamp amp meter was not apparently working when I tried to measure pump after engine was acting up. Tried measuring the high pressure pump and the low pressure with the key being turned off to on but neither seemed to register amp flow.

  14. #29
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    So this is a gen1 correct ? So If you have checked pressures on fuel and ok then - possibly coils if gen 1 since I thought I read that was an issue early on . So do you just check ohms on them - cold and hot ? The only issues I read were stuck fuel pumps if sat and i have heard you just run backwards to unstick to loosen . Early on in this thread it was mentioned coils . Thought that would set a code . Keep at it and suspect listen to early thread additions of coils being issue . And of course connections and wireing looked at closely . All I know is look at basics and move forward only once those basics are ruled out . Sounds like fuel pressure and pump are good - compressor difference pressures . Won' a DDT see a coil pack problem ?

  15. #30
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    It's a 2006 powerhead not sure how to tell what gen. Just shrader valves on the fuel rail and air rail, there aren't shraders on my vst. It's super cold today (40s)and the problem has gone away again lol.

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