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  1. #1
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    1998 merc 200 efi loss of high end rpms

    So I just bought this boat with a 98 merc 200 efi serial number is 0g624913. When I first bought the boat it had an alarm for what I was told the low oil alarm, they had receipts from the shop working on the high pressure fuel pump Ecu, etc so I took the receipts word for it that it was the oil cap. Needless to say it was the water separator not the low oil alarm. So after a few times out with the boat and it running fine, and emptying the fuel water separator, it started falling on its face like it’s not getting enough fuel at wot. It will come out of the hole great then about 5 -10 seconds later falls on its face and won’t run over 4000 rpms. Here is what all has been worked on/replaced that there are receipts and evidence of. The ecu was sent off to be re flashed and have the fuel pump drivers re done. High pressure fuel pump was replaced, pulse pump rebuilt (by me) fuel lines from top of tank to the pulse pump including primer bulb replaced. I should say when this happens the primer bulb remains firm. I checked my fuel pressures (key on engine off) and it was 36 psi then at 15 seconds after turning jet off it drops to 32 psi then at 30 it’s at 31 psi and 30 psi at 60 seconds after key off. I wasn’t able to get fuel pressures with it running as the nearest river is a half hour away and I don’t have the adapter to run mine on the hose (it has a jet pump so muffs don’t work) do these fuel pressures seem right? I’ve got a fuel filter ordered that should be here Thursday but I’m just hoping somebody can help me out with maybe some other stuff to look at in the mean time

  2. Member
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    #2
    I forgot to add, after the hole shot I can’t get the motor to rev over 4000 rpms. I can shut it down for a few seconds then come back out of the hole at 5500 but it immediately falls back on it’s face. If I take the fuel water separator off and dump it then re install it seems to get it back to running longer without falling on its face but it still does.

  3. Member
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    #3
    get some fresh gas in a portable tank and see if that helps . Bad gas in the boats gas tank could act like that and if the previous owner was having engine prolems who knows how old the gas is?
    You didn't mention but is the fuel primer bulb soft or collapsed indicating fuel starvation when you can't get full RPMs ?

  4. Member
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    #4
    Bulb stays primed. Motor will idle and run as normal when the issue happens. I’ve got a remote tank I can hook up and try. If bad gas is the issue how do you suggest I drain the tank? A simple transfer pump or is there a better option?

  5. Member
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    #5
    you gota fuel restriction somewhere , you have replaced filter haven't you ????
    .................................................. ...the scariest thing in life is the unknown ...................................

  6. Member
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    #6
    Filter hasn’t been replaced I ordered it after I found out the alarm was for the fuel/water sensor it should be here thursday. I’m going to check it out once I get that replaced. I’m really hoping it’s that and not something with the vst. I’m going to pull the fuel pickup line as well and replace it since it hasn’t been replaced yet... I’m really not even sure what the pickup is constructed of. The tank is a built in aluminum tank so it’s not the easiest task to just pull the pickup but I’m certainly going to pull it and replace it if possible

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    #7
    I should mention I’ve run about 20-30 gallons through the tank before I had any issues. I believe it’s a 20 gallon tank. Again hard to say because I’ve never run it empty.

  8. Member
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    #8
    clean everything from vst back to tank would not mess with tank yet,mkae sure it doesn't have antisiphon ball in tank fitting at hose connection
    .................................................. ...the scariest thing in life is the unknown ...................................

  9. Member
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    #9
    I had a boat years ago that I troubleshot and found a restriction in the fuel pick up tube in the tank . It would come out of the hole fine but after a short time running it would lose power and rpms would drop and boat would come off pad . I experimented with different engine speeds finding the higher rpms above midrange the faster it happened . If I slowly increased the throttle you could feel it when it would just start to happen and engine would start to oscillate 200-300 rpms (surging) and just keep doing it . Reduce the throttle a little and it would stop but increase the throttle and it would get worse . I was definitely running out of gas . Found a bunch of hair imbedded in the PU tube screen and I was perplexed on how it got into my gas tank . It was years later I figured out it had to be from a guy I used to fish against suspected of dirty tricks and who's wife just happened to run a beauty salon .

  10. Member
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    #10
    I found lots a stuff in tanks over the years but no hair, dang, Know what makes a good winner , A better looser ,he musta been a bad one
    .................................................. ...the scariest thing in life is the unknown ...................................

  11. Member
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    #11
    Good deal ya I will definitely check the fuel pickup probably drain the tank just to be on the safe side

  12. Member
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    #12
    Pickup is clear no clogs, tank is clean. Can’t change the pickup but it is a hard plastic tube that’s built into the tank. No check valve and screen appeared clean when I pumped the tank dry. Haven’t gotten it on the water yet but I just changed the fuel filter today. Hopefully that fuel filter being clogged is my issue...

  13. Member
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    #13
    Replaced the fuel filter/water separator still same issue. I’m going to try to drain the tank as when this happened I had sediment once again in the filter. Any other suggestions? Replaced the fuel lines from the tank (besides the pickup) to the fuel filter.

  14. Member
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    #14
    could run on separate fuel supply for a test to see if problem is in tank also
    .................................................. ...the scariest thing in life is the unknown ...................................

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    #15
    I’m going to give that a shot... but if the tank was causing the issue wouldn’t I be losing prime?

  16. Member
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    #16
    if there is a restriction before bulb , bulb may collapse, make sure bulb is not the problem ,seen many new aftermarkets bad outa the box, some are junk, #13 says you replaced filter the one one mtr correct ???? no others in line between mtr and tank
    .................................................. ...the scariest thing in life is the unknown ...................................

  17. Member
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    #17
    I’ll try getting a factory primer bulb and give that a shot as well. No other filters besides the spin on one on starboard side of the motor that I replaced along with the sensor.

  18. Member
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    #18
    Well put a different tank, primer bulb and fuel lines on the motor and still same issue. At this point I think I’m going to try to open up the vst and see if there’s any junk clogging the screen on the fuel pump. Past that I’m open to ideas of what to look at next. I did have the controls open to replace the piezo alarm but I didn’t mess with any of the throttle cables etc in there...

  19. Member
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    #19
    So finally figured my issue out it wasn’t motor related at all. My shift cable was worn out so my reverse gate on the jet was flipping up and choking off my motor when I was under power and moving. Kind of makes me feel like a bone head but to those running jet pumps in the future always scrutinize everything in the jet pump first before even messing with the motor.

  20. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #20
    Good catch- believe you had more than one thread going (next forum down is the correct one for your 2.5L, in the future). Easy fix!


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