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  1. #1
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    1989 Mercury Black Max 150 - problems with power, missing on cylinders

    Forgive me for what is likely to be a lengthy post, but the history is long and the bills have started to pile up. I don't know what else to do.
    I would appreciate any help or advice anyone could give to get me pointed in the right direction. I'm no mechanic by any stretch, but mechanically minded and my dad who's been helping me is a mechanic - albeit not a boat mechanic.

    The motor is a 1989 Mercury Black Max 150. serial - B313046

    Here's what happens: First, the boat won't idle, and when I get it moving and it finally does get up on plane it is still down on power, and I can hear the 6th cylinder cutting in and out. I think it's running on about 3-4 cylinders at idle.
    However, even though it seems to be missing on cylinders, they always have good spark, and they pour fuel out the exhaust.
    The motor runs like a complete dog out of the hole - I'm sure it's only hitting on about 3 cylinders.
    Compression is decent and consistent across the cylinders at 95-105 psi.
    We've taken the carbs apart and they look good. No concerns at all that we could see.
    When testing the motor on the muffs, it's cylinders 1,3,4 that don't seem to be firing, and thus, not on one bank. We tested this by pulling the wires while it's running and listening for engine note to change.
    I have changed the stator and the trigger and had no change to the performance of the motor.
    We have switched power packs around, and tried a different set from another motor and the problem stayed on the same cylinders.
    We have moved coils around and the problem stayed on the same cylinders.
    We checked the timing and it is where it's supposed to be. (i forget the details, but we confirmed it was set according to the manuals for the motor)

    I'm really at a loss here and could use some help if anyone has any suggestions.

    Thanks,
    Trevor

  2. #2
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    I have had similar issues with motors in the past mainley jet skis doing the same thing compression would be good spark would be good they will just run like crap and dump raw fuel out exhaust. and 99% of the time it turned out to be pistons were scuffed to much to allow it to get good combustion and would flood with gas. On those 3 cylinders you say it won't run on is that the 3 that have the lower compression of the 6? I usually like to see around 125 psi and 2.5l v6 mercury so 95 is kinda low to me. It may be worth pulling a head to see if you can see any scuffs on cylinders or have a leak down test done on cylinders also make sure you are checking compression when engine is at operating temp. Maybe sombody else has had this issue and can chime in there are some really good and smarts guys on here.

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  4. #3
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    I'll check the compression on those cylinders tonight when I get home and let you know. Thanks for the suggestion.

  5. #4
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    comp. sucks ta start with if its right.. anytime ya take wh's apart, clean and put back together ya better use NEW gaskets completely thru 'em, check needle and seats, floats and float level......simple clean and put back together (no mater how good tha gaskets look and come apart) will result in a turd most of tha time.......jmo
    Last edited by tlwjkw; 06-22-2015 at 08:31 AM.

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  7. #5
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    google outboard decarb. you need to decarb that motor, it may help your low compression. you need to order a DVA adapter $30 and it will work with most multi meters. and go to CDI electronics web site and download the free troubleshooting guide and dva chart. sounds like you have a bad power pack or the ground wire going to the power pack is bad you can ohm test the ground wire to the battery ground, should be 0 resistance. I have cleaned out plenty of carbs with out replacing the gaskets and I have had very positive results.

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  9. #6
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    Need a manual and correct tools like a dva or you will spend needless money and drive yourself crazy trying to fix without.

    Dave
    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

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  11. #7
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    Stator.

  12. #8
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    Thanks for the feedback everyone. I went and bought a new compression test tool. (The one I was using had the rubber nub instead of threading into the spark plug hole. I was worried I may have been missing some psi's!)
    The compression turned out to be much better than I originally had from the old tester:
    cyl 1: 111
    cyl 2: 115
    cyl 3: 115
    cyl 4: 115
    cyl 5: 115
    cyl 6: 118

    I looked online to pick up a DVA, but I'm in Canada and the things appear to be rare. I'll keep looking tonight and try to get one ordered if I can find one.
    I do have a full manual for the motor that I picked up a year or so ago. It's an online/scanned book, but it does the trick.

    I also picked up some Sea Foam today, but not sure the best way to use it. Lots of online stuff, but it seems that some people do a "shock test", and others just add it as part of the fuel mix, and yet others add it to the crankcase. Any advice on what I should do? I'm leaning toward the shock test - 16 oz of SF, 3/4 gal of fuel. (the engine is oil injected so i won't add any oil to the mix)

    And for perfmarine1, I replaced the stator this weekend - it was the last thing I did before posting here.

    Thanks,
    Trevor

  13. #9
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    If you run a shock mix from a remote tank you will get oil. Better normal compression numbers now so doubt carbon is your full issue.

    Dave
    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

  14. #10
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    http://www.tooldiscounter.com/ItemDi...FYI7aQodWrUAUw
    they ship to canada. first one that came up on google. not sure why you could not find it.
    do another decarb and see if we can get those numbers over all 120.

  15. #11
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    Have you removed the idle stabilizer? How about the fuel pump have you rebuilt that, it could be leaking into motor. Also make sure the trigger is free and moving with arm to advance. Check the voltage to the green wires to the coils, should all be the same, 150+ If I remember. DVA
    Last edited by perfmarine1; 06-23-2015 at 10:51 AM.

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  17. #12
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    Thanks Sparkieboat. Unfortunately, it's the cost to have it shipped to Canada and the duty on top that stings (sometimes the shipping and duty is $50 or more for stuff like that). And the link you sent won't even estimate the cost to ship it, so I'd have to roll the dice and hope for the best... However, I talked to our maintenance manager today about making a DVA (just where to buy parts) and he told they have a peak reading meter. He let me borrow for a couple weeks to fix my motor. And I'll grab the manual you mentioned from CDI and try to get the testing done tonight or tomorrow night.

    perfmarine1, I'll check the trigger and check the voltage to the coils. I bought an ignition spark tester today good to 40kv, so hopefully it will give me a better idea about the coil output (assuming they normally output less than 40kv).

    Thanks for the continued help everyone. I'll post back as soon as I have some results to share.

    Trevor

  18. #13
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    If your close to the water disconnect the idle stabilizer and try it. Seen those things cause some weird things before.

    Dave
    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

  19. #14
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    Thanks Dave. I think I'm going to head to the water tomorrow night. Greg also mentioned the idle stabilizer. If it's a matter of disconnecting the wires from the ground and power packs, I can do that tomorrow night at the lake and see what happens.

    Greg - I didn't get a chance to check the leads to the coils tonight, but will check them tomorrow. The trigger arm moves forward about 1" with gentle pressure and springs right back into place. And in answer to your previous note, I haven't touched the fuel pump. What do you think it would be doing to cause the miss? I don't understand how it leaking into the engine causes the miss because I don't understand how it's integrated into the engine.

    Here's what I found when I checked the stator tonight:
    engine at about 1750-2000 rpm
    Blue/white: 195V (ramped up to about 200, then back to 180, then stabilized around 195 for both blues)
    Blue: 195V
    Red/white: 120V (ramped up to about 130V, then settled back around 120-123V for both reds)
    Red: 120V

    The two red's surprised me since the CDI paper says they should be "over 20V" - well, i'm way over! Is this a bad thing?

    I followed all of the CDI instructions for the weak hole shot and intermittent high RPM issues since that's really what I've been experiencing. I disconnected the rectifier for all of my testing. If the rectifier is pooched, could that be causing my batteries to fail early (the new one from last year was stored inside, but was hooped this year), and the tachometer to go crazy when it's connected?

    I did rotate the stator both directions from where I had it placed. Moving it the second time may have helped. Honestly, I've listened to it run so many times now, I'm not sure whether the miss is there while it's just sitting on muffs. Hence, the trip to the lake tomorrow or Thursday.

    I may try the shock treatment tomorrow too. We'll see how I'm doing for time.

    Thanks everyone.

    Trevor
    Last edited by trevstar; 06-23-2015 at 08:00 PM.

  20. #15
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    you need to do a search on disconnecting your idle stabilizer. they should be disconnected as failure at high rpms can destroy your engine. your WOT timing has to be adjusted to 25 I think. standing behind the engine, it is on the top left side. a 2 or 3 inch square or rectangle box with about 3 wires coming out of it. If i remember right. do a google search. the process should come up. you should test your voltage regulator.

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