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  1. #1
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    Aug 2020
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    19

    1994 Mercury 150hp XRI EFI Black Max idle issues

    I have had this motor for 5 years and has always ran very good, no issues at all. Put it up for the winter and right out of the box it has developed an idle issue while in the water. It will idle all day log on the muffs in the driveway but just not in the water. Once I get it going it will run like a bat out of hell, just like it always has. After a lot of research, I am having a hard time find my exact issue, so I figured I would post on here to see if anyone has any other directions that I need to start checking. Below I will list what I have done.
    • New water/fuel filter (after this filled it with premium and ran a complete can of seafoam through it, but it didn't solver the issue)
    • Then I did the below
    • New Plugs
    • Rebuilt the pulse pump (and no the electric pump is not noisy)
    • New fuel hose and primer bulb
    • Took compression test, after I did it I then did research and found that I didn't do it completely correct, I did not have the throttle wide open it was closed, however I still was reading 110 psi across all 6 cylinders


    So after all that I started it up in the driveway and it idled at 750 rpm (which to me is low) took it to the lake and started it up, while it was better it only wanted to idle at 500 rpm, again to me that is too low. It states no more than 750 rpm while in gear. I am able to get it in gear at that low idle and get it to the 750 rpm, but when I bring it back to neutral it wants to and then it will die.

    So I have reading about the Idle Stabilizer box, could this be the culprit?
    Also looking in the manual it talks about LOW SPEED/HIGH SPEED SPARK ADVANCE could this be the culprit?
    Does this motor have both?
    Because when looking for them it has 2 identical boxes mounted on the motor, one in on top of the power head and the other is mounted on the port side of the motor.

    Any help or suggestion would be great.

  2. Member
    Join Date
    Mar 2018
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    Ashland city tn
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    171
    #2
    Alot people on here don't like to remove the black box or boxes , if I were mine I'd throw em n trash and set the timing on idle and wot and run it

  3. Member
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    Aug 2020
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    Chester, Illinois
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    #3
    Ya, I was thinking more on this today, and I think I am going to check the timing and see what it shows, and go from there.

  4. Member
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    Jun 2013
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    #4
    top is warning module side is idle stabilizer
    .................................................. ...the scariest thing in life is the unknown ...................................

  5. Member
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    Aug 2020
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    Chester, Illinois
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    #5
    So I am still messing with this thing and it has developed more issues.
    Now once it starts it clearly isn't hitting on all cylinders.
    It idles at about 750 rpm's then it starts to spit and sputter and then dies.
    It won't start up until it sits for several minutes, then it's a repeat.
    I did put a timing light on each cylinder and it will flash while cranking.
    I cleaned the post electric fuel pump filter screen and installed a new pre filter screen.
    Also installed a new fuel pump it does push fuel to the specs as did the old one, while running it holds at 35psi but once it spits and sputters I can watch the pressure go down.
    I disconnected the idle stabilizer but nothing changed.
    So i'm at a loss to what to try and check or replace next, because starting to get into the expensive stuff, any suggestions would be great

  6. Member
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    Aug 2020
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    Chester, Illinois
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    #6
    Did the ohm's test on the stater and trigger, both came in spec, so ordered 2 new switch boxes, we will see

  7. Member
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    Jun 2013
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    #7
    if fuel psi is falling mtr will leanout and die ,not switch box related ,posssible ECU related
    .................................................. ...the scariest thing in life is the unknown ...................................

  8. Member
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    Aug 2020
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    Chester, Illinois
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    #8
    SSSHHHHH I didn't want to say that out loud and it doesn't appear they are available anymore, or at least not at my first search, not to mention the sticker shock. Switch boxes already on the way, so I will try that and go from there. What is an option if it is the ECU and I can't get one?

  9. Member
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    Jun 2013
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    #9
    ,repair , or bypass, we'll talk about that later
    .................................................. ...the scariest thing in life is the unknown ...................................

  10. Member
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    Aug 2020
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    Chester, Illinois
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    #10
    Sounds good, I do have a place 30 minutes from me that repairs ECU's. SIA Electronics

  11. Member
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    Jan 2012
    Location
    Houston
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    1,165
    #11
    Are you still running stock reeds? Might be worth checking them and replacing them with CCM or Ducas. A chipped reed will make one spit.
    90 Shadow 20' Mod V w/ 200 Merc - Total resto and loving it!
    Here's my build from cap-off to boat in the water.
    http://www.bbcboards.net/showthread.php?t=336645

  12. Member
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    Aug 2020
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    Chester, Illinois
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    #12
    Well JOE54 you where correct, wasn't the switch boxes. So where do you suggest I send the ECM for test and repair. The place close to me doesn't repair outboards ECU, they gave me a number to Simon Performance out of California, so I called them and ouch very expensive, but at this moment it's a paper weight so need to send it some where.

  13. Member
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    #13
    afraid of that , you test it to confirm its bad , bypass ecu for pump activation
    .................................................. ...the scariest thing in life is the unknown ...................................

  14. Member
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    Chester, Illinois
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    #14
    Actually JOE, I already removed the ECU and would just as soon send it off to be check out and repaired if need be. So who do you suggest?

  15. Member
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    #15
    personaly i would have to know its the problem , SIMON good as any at least youll have written guarrantee !!!!!
    .................................................. ...the scariest thing in life is the unknown ...................................

  16. Member
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    #16
    I'm tired of messing with it, so I'm sending it off to Simon then, if it checks out okay then I'll move on, if not it's there for the repair.

  17. Member
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    Chester, Illinois
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    #17
    Well just heard back from Simon Performance. The did find bad drivers for injectors and fuel pump. So they fixed it and it is on it's way back. Keeping fingers crossed that between those issues and everything else I did prior, solves all issues. I will report back once it returns and give it a go.

  18. Member luvdmymerc's Avatar
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    #18
    Keep us posted....

  19. Member
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    #19
    ^^^^^^+ 1 SSSSSHHHHHHH i told ya let us know
    .................................................. ...the scariest thing in life is the unknown ...................................

  20. Member
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    Aug 2020
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    Chester, Illinois
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    #20
    Update: Got the ECU back, installed it and pulled it out of the garage, hooked up the muffs and started it up. Immediately noticed a difference in the sound and thought sweet it is fixed, then after about 7 to 10 minutes it died. had a hard time starting it until I pumped the bulb back up, then she started. So I let it run a while and shut it off. Since I was already hooked up I took it to the lake to see if it would idle in the water (since that was the original issue at the beginning) backed it in and started it up and it stayed idling for a long time then died (pumping bulb made no difference before it died). Started right up without pumping the bulb so I put it in gear and it stayed running (another of the original issues), took out of gear and stayed running (again one of the original issue). Did this repeatedly for about 30 minutes and for the most part everything was working correctly (except on occasion it would die), except I feel the RPM's are still too low.
    >Out of gear idling in water 700 to 750 rpms
    > In gear in water 650 to 700 rpms (shouldn't it up the rpm's? it still has the idle stabilizer)
    > lower unit up or down no real difference, maybe a little better up
    I did notice more than more than normal extra blue smoke, so I am thinking even though these where new plugs and it wasn't hitting on all cylinders that they may be slightly oily not to mention I did put some injector cleaner and sta-bil in the tank (and seafoam prior). So next weekend I am going to take it out on a fresh tank of gas and run it to see if it gets better. While it is 90% better and usable, I think it could be better.

    I do have one question, if you remember from my first post and I listed everything I have done when I changed the fuel line and bulb I went with 3/8" versus 5/16", do you think that could be causing any issues, I wouldn't think so but I don't now how much an 1/8" in hose size would matter.

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