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  1. #1
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    Troubleshooting electrical issues in early OMC V4s

    Hi. I have been keeping an eye out for an older cheap motor to do a bit of work on and get up to scratch. 90-140hp range. I was originally looking for a tower of power but general advice from here was that Black Max V6s were a significant improvement. Problem is that I rarely see them come up for sale in my area (i'm in Australia). While I am continuing to keep an eye out for one, I do see a few OMC V4s come up. I don't have any strong brand loyalty and am wondering if these are an option.

    Often these OMC motors claim to have good mechanicals and compression but some kind of electrical issue. One example is a 1978 115hp Johnson for sale with "no spark" for $500. This is about the most I would want to spend on a motor with unknown issues as would have to factor in a rebuild. In this case the seller claims "good compression" which I would want to investigate further. It is obvious that the person has tried to troubleshoot the issue and has given up or realized it is not cost effective. It comes with spare coils and wiring loom and is on a hoist.

    I have read a bit about the electrical issues with these older OMC motors. I'm not an expert on the differences between years but the CDI on some models seemed very primitive from what I gather. They rely on good battery, connections and starter motor to get the RPMs required to produce the spark. This scares me a little bit in terms of reliability. Also I have come across a few threads where despite following troubleshooting guides (such as CDI electronics) they have apparently failed to diagnose the issue which ranges from no spark on a single cylinder to no spark at all to no spark only after the motor sits for a few days.

    My questions are:

    Are the electrics problematic enough that when considering the age of these motors now they are likely to have ongoing reliability issues?
    Is there a particular year when they sorted this stuff out?
    Is it hard to troubleshoot these electrical issues compared to the old TOP?

    One thing that does attract me to these over the TOP is the ability to rebuild top end more easily.

  2. #2
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    from 73 and up the ignition was basically the same and easy to troubleshoot.
    I would only go back as far as 78 to get the integral trim. ( plus a 77 140, just about a collectors item now)
    They are tough engines thats why they are still around

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  4. #3
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    Is it the larger cylinder on the right that is integrated trim? From the cowl (assuming original) it looks like a 78 model - is this correct?
    Attached Thumbnails Attached Thumbnails 230752324_10225850543840823_6066422547084595194_n.jpg  

  5. #4
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    Quote Originally Posted by Gilera View Post
    Is it the larger cylinder on the right that is integrated trim? From the cowl (assuming original) it looks like a 78 model - is this correct?
    NO thats the old trim, not worth getting involved with.
    FYI slight difference in powerhead bolt pattern from that to he later integral trim where everything is between the stern brackets, 2 little rams for tim and one cylinder in the middle.

  6. #5
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    V4 OMCs of that era are great engines. Easy to build and diagnose. The few that I have had all came to me with electrical issues, always something easy like a bad coil or ignition switch. Like you said, do a comp test, if that passes, grab it!
    1977 Hydrostream Vector 2.5 Promax

  7. #6
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    I have been in contact with the seller and he tells me that the compression was between 110 an 120 on all four cylinders when tested a few weeks ago. He has not tested trim/tilt which i guess means that he has not used the motor. He said the spark was weak and he bought 4 2nd hand coils to see if it would help but it didn't improve. He claims that there is no corrosion anywhere on the motor and suspects that it was primarily used in freshwater.

    So what is the issue with the external trim module. Is it prone to failure? Hard to rebuild?

  8. #7
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    Quote Originally Posted by Gilera View Post
    I have been in contact with the seller and he tells me that the compression was between 110 an 120 on all four cylinders when tested a few weeks ago. He has not tested trim/tilt which i guess means that he has not used the motor. He said the spark was weak and he bought 4 2nd hand coils to see if it would help but it didn't improve. He claims that there is no corrosion anywhere on the motor and suspects that it was primarily used in freshwater.

    So what is the issue with the external trim module. Is it prone to failure? Hard to rebuild?
    Hard to rebuild and I doubt there are are any parts anywhere plus you need to find someone that knows how to fix it.
    If its a hydroshift gearbox that will also be hard to find parts although they worked forever as long as they had clean oil

  9. #8
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    IMO I would buy that motor...... it's clean......not ragged out.

  10. #9
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    Quote Originally Posted by Dave S View Post
    IMO I would buy that motor...... it's clean......not ragged out.
    sure it all could still work for years..

  11. #10
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    Im itching to go and look at the motor but i live on the border and it is closed to everyone except essential workers due to COVID. Hopefully will be lifted soon. In the meantime I did see another Evinrude 115 that had the integrated trim on a nice 16ft deep V runabout in what looked like really good condition for $5000. Also in the next state. Sold after 1 day.

  12. #11
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    Like power said 78 or newer is better stay away from pre 73. The ignition on those motors is as reliable as any outboard, it runs off the stator so it doesn't use the battery except for starting. The more recent problems have been with aftermarket parts. I could roll of a list of older crossflow engines that i have had/ran and none have ever had ignition problems, i cant say that for some newer stuff... IMO you are better off buying new old stock in the box from ebay than new aftermarket parts..

  13. #12
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    I found out a bit more info from the seller while I am waiting for the border to open. Apparently the motor sat for a long time prior to him buying it during which time the previous owner repainted the hull (motor was removed from boat). When the current owner purchased it the motor was in the down position and the trim module had not been connected back up. The current owner never got to connect and test the tilt/trim as he was primarily interested in getting the motor running. I feel like I now have to assume that something could be wrong with the trim/tilt. Since you guys alerted me to the fact that the trim module can be problematic I have read a few forum threads. It does seem like quite a few people had had a lot of trouble isolating the cause of slow leaks causing the motor to drop slowly over time. Some seem to have never figured it out despite replacing just about every O ring and seal. I saw a few reports of people finding water inside the canister. As I would be leaving the boat in the water for periods of time I could not live with non-functioning trim/tilt.

    The engine is now on an engine crane. They guy said I could hook up a battery to it (there are 3 wires in the cable leading from the top of the trim- which ones to connect?) but I guess this will only tell me if the motor and mechanism are operational, not if they will sag back down over time. Are there any other tests I could perform?

    Worst case scenario, is there a way to retro fit another module in its place?

    Seems a shame to let such a clean looking motor go but if I can't be confident that I'm not up for a big job and big $$ rebuilding the tnt (assuming I can source the parts here in Australia) then i'll just have to keep looking.

  14. #13
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    Honestly, and I think guys will back me up here: a motor with no spark is actually way easier to diagnose vs. one with intermittent spark/ignition issues. Just remember super simple: spark is produced by only a few components. Charge coil under the flywheel ("charges" the capacitor in the pack), sensor coil/timer base/trigger sends a tiny .3-2.5v signal to the pack when to fire, and of course the coils (primary sends voltage to the large secondary) and on to the plug wires. a DVA adapter + multimeter and OEM manual will have you pinpoint the issue in 10 minutes without blindly replacing parts!

  15. #14
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    As for the trim: basically any trim for a v4/v6 crossflow will work, just as long as its not the newer 2 pin fastrak system made from about 1992 on up . replacing it is very straightforward: remove the 3 screws on either side, plus the big drift pin on top, and out she comes (well, some elbow grease too). I'm sure lots of guys rebuild these, but I just swap units. not worth the time to rebuild when used ones can be had for $250.

  16. #15
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    Yea like they said the 4 cylinder omcs are great motors.. Easy enough to diagnose and work on.
    If all the Electronics are original you could replace everything and have all new electronics for not to much $$ if you look/shop a bit could even go digital.(dont have to replace everything either can use stock stator just need to take out the power coil ..real easy).going digital solves the hard start problem it uses power from the battery for spark so dont need the 600 rpm to start and the other small problems they had.. can literally start my v6s with a really weak battery and start with a tap of the key dont even make a full rotation and start.
    Also if the trim unit leaks a bit because seals are leaking
    Get a bottle of ATP AT-205 reseal and dump that in the fluid let sit a bit then run the trim up and down a bunch of times and will be ready to go .. and can just leave it in there.. have used it plenty of times for units that were leaking.. NOW if the seals are really shot can try it but have to be realistic too.
    Sometimes I talk to myself...then we both just laugh and laugh


    '84 Checkmate Convincor
    Twin v6 closed deck Evinrude loopers Ported,2.7 heads,cooling mods
    milled finger ported to match vertex pistons,
    All casting slag removed
    Sleeves in opposite so no idle reliefs
    Offshore exhaust mids
    152 psi comp,balanced pistons and rods,Stuffed, 106 pullovers
    CDI 8500 digital ignitions ..Boyesen reeds..And more..

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