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Post Options Post Options   Likes (0) Likes(0)   Quote Anderson17 Quote  Post ReplyReply Direct Link To This Post Topic: Mercury 115 CT missing
    Posted: 17 Dec 2024 at 7:48am
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I have a Merc 115 CT . 2019. 200hours .
After trolling for a few hours or left in idle for deep drops the engine misfires badly when trying to up the rpm’s and get up on the plane. Usually I can clear it after giving it a bit of stick for a couple on mins . It will only do this after running at low rpm’s for a longish time . When driving from point a-b for a regular fish it’s fine.
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Post Options Post Options   Likes (0) Likes(0)   Quote Telecaster Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2024 at 8:53am
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Wonder if it is getting hot due to less water flow at low RPM, and vaporising fuel in the line? Has the impeller/thermostat been replaced lately?
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Post Options Post Options   Likes (0) Likes(0)   Quote Anderson17 Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2024 at 9:58am
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I don’t think it’s getting hot. Did get all that changed at last service. I asked one boat mechanic and he thought it could be the computer thinking the engine is cold and putting more fuel in it. But just wounded if anyone else has had the same issue
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2024 at 12:09pm
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Have tried pumping choke,had a simular issue with a 2005 90hp mariner after a service and pumped key while running,coughed a bit no issue since.
"Times up"
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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2024 at 1:24pm
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I think the days of diagnosing these sorts of issues by what we see and hear might be numbered. The starting point might now be a laptop to check for error codes....
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Post Options Post Options   Likes (0) Likes(0)   Quote Tonto2 Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2024 at 4:05pm
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Do you have a water seperator fitted?
slowly going where everyone else has already been
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2024 at 9:55pm
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I have the same motor. It's only 23 hours old though and hasn't missed a beat surprisingly. I'd be looking at fuel and spark plugs with those symptoms.

Drain the water separator/filter onto a patch of concrete and you will see if there is water in the gas. Check the plugs but you will need to know what you're looking for. Besides the plugs on a modern 4 stroke should be well good after those few hours.

Hopefully you have a good local dealer who can figure it out if it's more that that
Best gurnard fisherman in my street
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Post Options Post Options   Likes (0) Likes(0)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 18 Dec 2024 at 7:38am
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Sounds like a coil pack, as said above time to take it a outbourd tech and look at the fault codes.
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Post Options Post Options   Likes (0) Likes(0)   Quote rowboat bob Quote  Post ReplyReply Direct Link To This Post Posted: 18 Dec 2024 at 7:47am
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I have the same motor and it says in the manual or in some you tube stuff I watched before buying that they don't like idling and that idling is not recommended for more than a minute at a time. I've done a fair bit of trolling on mine with no problems but at 7knots so well above idling. Good luck
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Post Options Post Options   Likes (0) Likes(0)   Quote Joker Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan 2025 at 3:57pm
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My son in Aus had the exact same problem recently. It was driving him insane and after 3 different mechanics they found the problem to be a cracked HT lead arcing. It was only found because the mechanic got a belt. Be worthwhile running your hands over the leads when the problem is happening.
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Post Options Post Options   Likes (0) Likes(0)   Quote kimber7wsm Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 6:26am
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What Joker said makes complete sense. When it's idling it'll be a little cooler as you power it for a while it warms up. When the lead is cool the crack will form a gap, causing it to arc across. As the engine and lead warms the gap closes, no more arc and runs perfect. I had an HT lead on car do exactly the same thing.

If that's is the case it is likely no fault code, as the engine doesn't have sensors on the leads, so can't detect anything wrong.

I would buy a spare lead and next time it does it (I would try and make it happen some where safe, like 2 minutes from the ramp or even better drum in backyard), then you can pull one lead if the problem gets worse then you know it's not that lead. If it doesn't then it's that lead and you replace it with spare and bingo engine fixed. Worse case scenario that doesn't work and you have a spare lead.
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 6:33am
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Originally posted by kimber7wsm kimber7wsm wrote:

What Joker said makes complete sense. When it's idling it'll be a little cooler as you power it for a while it warms up. When the lead is cool the crack will form a gap, causing it to arc across. As the engine and lead warms the gap closes, no more arc and runs perfect. I had an HT lead on car do exactly the same thing.

If that's is the case it is likely no fault code, as the engine doesn't have sensors on the leads, so can't detect anything wrong.

I would buy a spare lead and next time it does it (I would try and make it happen some where safe, like 2 minutes from the ramp or even better drum in backyard), then you can pull one lead if the problem gets worse then you know it's not that lead. If it doesn't then it's that lead and you replace it with spare and bingo engine fixed. Worse case scenario that doesn't work and you have a spare lead.
Get a volt meter and test each lead. if faulty lead will have a lower reading than others due to cable breaking down. Beter to test now than om water if in case not a lead.
"Times up"
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 9:32am
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You wont be able to test a spark plug lead voltage with an ordinary voltmeter.
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 9:44am
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Correct - was waiting for someone to point it out.
The possible issue is a leakage with a broken insulation. The conductivity/resistance of the leads will all test the same with a voltmeter - unless there is a permanently faulty connection - which would misfire all the time.
Alan
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 3:35pm
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Set your meter to OHMs place probe at each end of lead and there is your reading,if you get a different reading to others replace.Should read 0 ohms just got boy to do mine as a test. Seeing how some say you cant measure resistance with multi meter

"Times up"
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 6:34pm
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Originally posted by Pcj Pcj wrote:

Set your meter to OHMs place probe at each end of lead and there is your reading,if you get a different reading to others replace.Should read 0 ohms just got boy to do mine as a test. Seeing how some say you cant measure resistance with multi meter


Um no. I didn't say that. Your original advise was to use a voltmeter. A multimeter will read ohms and volts plus a heap more stuff. An ohm meter will show discrepancies with the conducting part of the lead but won't account for insulation leakage voltage. Trust me, I'm a rocket doctor. Well ok I'm just a retired sparkie. While this may seem like pedantics to some, it would be a very bad thing to test a HV lead with a voltmeter for two reasons: you will get a nasty shock & your voltmeter will be buggered.

There are two parts in determining the effectiveness of an HV lead. The resistance and the insulation resistance.
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 6:51pm
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Originally posted by smudge smudge wrote:

Originally posted by Pcj Pcj wrote:

Set your meter to OHMs place probe at each end of lead and there is your reading,if you get a different reading to others replace.Should read 0 ohms just got boy to do mine as a test. Seeing how some say you cant measure resistance with multi meter


Um no. I didn't say that. Your original advise was to use a voltmeter. A multimeter will read ohms and volts plus a heap more stuff. An ohm meter will show discrepancies with the conducting part of the lead but won't account for insulation leakage voltage. Trust me, I'm a rocket doctor. Well ok I'm just a retired sparkie. While this may seem like pedantics to some, it would be a very bad thing to test a HV lead with a voltmeter for two reasons: you will get a nasty shock & your voltmeter will be buggered.

There are two parts in determining the effectiveness of an HV lead. The resistance and the insulation resistance.
But taking leads off,non running motor you get a good indication.Boy has masters in robotics and Megatronics . If you get one lead with a dodgey reading swap out for new.
"Times up"
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 7:06pm
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But that is not the symptom of the issue. A multi meter won't help with that one.
Your approach/advice is incorrect.
Alan
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 7:11pm
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Originally posted by Alan L Alan L wrote:

But that is not the symptom of the issue. A multi meter won't help with that one.
Your approach/advice is incorrect.
Alan
process of elimination as  kimber7wsm  posted 6.30am today 


"Times up"
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Post Options Post Options   Likes (0) Likes(0)   Quote Keith C Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2025 at 9:21pm
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Might need some popcorn while we "spectate". 😄
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