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Intermittent no sparks, finally not at all

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  • Intermittent no sparks, finally not at all

    - Yamaha 115CETO (model 6N6), 2-stroke, 1996
    - CDI-box on starboard side, below rectifier
    - Red wire from engine tank oil sensor NOT connected to CDI-box via R/L - wire BUT to pink (P) termosensor wire, via a 1" cylindrical component, seemingly a diode, blocking current from oil sensor to termosensor pink wire ?
    - NO ground (grey/black) from termosensor wire to trim sensor's grey cable (as some electrical diagrams shows)
    - NO remote oil tank
    - NO gauges
    - Trim sensor SHOULD NOT be connected, but loose end, BUT turns out to BE CONNECTED to Y, Y/R, G, G/R 4-pole wire , supposed to go to oil alarm/meter EDIT: before, bold text "oil alarm/meter" said "trim meter"


    1. Engine overheats at 3/4 WOT. Alarm triggered BUT (at least as the engine's user told) NO rev. limiting !

    2. Engine taken to authorized Yamaha work shop. Impeller shown to be OK, but changed. High pressure water cleaning of lower unit. Now "only" overheat alarm at 4/4 WOT.

    3. Taken to work shop second time to "clean jackets" under cylinder heads. Seems the thermosensors not changed. If thermostats changed, I don't know (not me being in contact with work shop). NO improvement of overheat alarm.

    4. Shortly after being to last repair, engine begins to stop abruptly, intermittently, to finally after some weeks, quitting totally.

    5. I see the engine first time. NO sparks. NO voltage output from CDI-box (DVA-measurement) with kill-switch disconnected. Charger- and pulser-coils within specs. both ohm and voltage. NO contact to ground. Ignition coils ohm-measuring OK.

    6. Remarkable finding : the Y, Y/R, G, G/R 4-pole wire from oil unit is connected to trim sensor (orange, black, pink; gray lose end) !!!!!

    Could these misconnected wires be the reason for the CDI-box failure?
    Could it have been misconnected before the work shop visit?
    If so, could that misconnection be the reason for the rev. limiter NOT kicking in at overheat alarm?
    If else, what could have caused this sudden onset random non-spark firing and final death of sparks?

    Those intermittent, and then final failures of CDI-boxes, can it be caused by simply a soldering inside the box getting loose, stirred by vibrations, causing the intermittent behavior, and then finally getting loose totally ?

    Very much tankful for input from mechanics/autodidacts with understanding of what's inside the oil unit and the CDI-box.

    Thanks in advance !
    Last edited by yamaha-115-96; 06-20-2012, 04:39 AM. Reason: ... go to oil alarm/meter (instead of trim meter!!)
    Yamaha 2 stroke, -96, 115hp

  • #2
    Did you disconnect the 4 pin connector that was not suppose to be hooked up?
    and did you try disconnecting the white wire at the CDI(kill wire from key switch and Kill switch) and see if spark came back?
    The white wire is grounded by those switches to kill the spark to stop the motor, so maybe the wire harness or one of the switches is bad.

    Not sure what would happen if it was hooked up like that, maybe Rodbolt17 or someone else with the proper knowledge will be able to answer that for you


    • #3
      Thank you for reply!

      Yes, I unhooked the two wire bundles, and also disconnected the (white) kill-switch.

      After that I built a "peak voltage meter" ( and found the CDI was dead on the output side.

      Problem is I don't know how the "oil unit part" of the misconnection, ends up in the oil unit box. I found a "ohm-diagram" here: Yamaha c115 Outboard Service Manual , but that shows Y, L, B, Br, G/R, G/B, R as output wires and my has Y, L, B, Br, G/R, G, Y/R as output and the red (R) from engine oil tank sensor, going to pink (P) termosensor wire (over a diode? ) .

      It is the Y-Y/R-G-G/R plug that becomes "shorted" over a (tilt) variable resistor in the trim sensor:

      Yellow to Orange
      Yellow-Red stripe to Black
      Green to Grey
      Green-Red stripe to Pink

      When using the above "wobbly" information, it seems (+) is conveyed via yellow (ignition on) , over ~500-1000ohm resistor (trim sensor) to ground (B) (inside oil unit) . When the termoalarm went off, that should have been conveyed to pink (P) output on CDI.

      Direct connection red (R) to pink (P) should be stopped by this "diode" (see earlier post) I think. It is the ohm-reading over G/W to P (on CDI) that misreads !! IN oil unit, G/R shall only lead to R (over 16-24 k? Ohm) in one direction, infinity in the other, BUT due to the "trim meter short" , it connects over the ~500-1000 Ohm) !!!

      It might be that the unlucky CDI-frying was due to COMBO:

      the misconnect + ignition on + "unlucky tilt-position" + termoalarm goes off !!!

      I don't want to fry the new CDI again !! It is prohibitively expensive where I live, ~1500$ sic! from Yamaha. I think I have spotted a reseller of an "aftermarket" box from something called cdielectronics, for "just" 600$

      When the engine is fixed, I might open the oil unit and CDI-box and simulate all the mess in LTspice. I doubt I want to delve that deep though

      Thanks again for reply, and if you have a super-guru on these things here, please let him know about my problem, that btw. the work shop has not answered (e-mail and phone)
      Yamaha 2 stroke, -96, 115hp


      • #4
        Connection of two square gauge connectors shouldn't damage CDI unit but will activate alarm and rpm reduction, do need to test diode in pink wire is working properly.
        Yamaha Outboard Parts


        • #5
          Thanx very much for reply (bow)

          For sake of clarity, I'm living in Sweden, if they have any specifics of the engine there.

          The two square (4-pole) connectors don't go to any meter/gauge.

          The "trim sensor" connector (O, P, B: Grey free) goes to the sensor (which btw. was stuck) sitting on the transom part of engine.

          The Y, Y/R, G, G/R connector (which I think shall be connected to a "oil meter" , that I don't have) , goes in to the "oil unit".

          The ~1,5 x 0,5 cm cylindrical "thingy" that connects the red (R) wire from engine oil tank "sensor" to pink (P) termowire, I assume is a "diode" (I'm an autodidact "electrowizzard" a.k.a. a die hard amateur ) , measured infinite resistance in one direction and 5M ? ohm (5K ohm ?? ) in other direction. The boat sits on land on an outer island in Stockholm archipelago, so can't check now, but will Friday coming Midsummer Eve, but my bad memory thinks it was "infinity-block" in direction from oil sensor to termowire.

          There is another "thingy" not described in manuals, that is a rectangular black "box" of some ~1 x 2 x 1,5 cm, into which a black, lightblue and lightgreen wire goes. It sits on the port (babord) side under PTT-relay and gets its wires from the harness coming from starboard side ! Thus I haven't been able to measure what component it is. I assume it might be some "smoothing out" component connected to the PTT-circuitry.

          Additional info: those running the boat when it "overheated" say there was NO rpm-reduction, but that is "wobbly" info (reading: not outboard mechanics).

          I pray to higher powers that whatever mishap that caused the CDI-collapse, is gone, when I get my hands on a new box and install it.

          Which leads to the question: What can cause failure of a CDI-box, seemingly in tight time connection to after the last repair, "cleaning" the cylinder head and termostats? Switching of polarity somewhere? Disconnection of battery whilst running? Starting the engine with boat-side work shop battery/charger? Test cranking with spark wires not properly connected? Short in harness somewhere?

          Additional info : It was "real" overheating, especially one cylinder bank was burning hotter than the other side. There was also a weak tell-tale flow, which btw. went to a standstill when increasing throttle ! Has that to do with the "poppet valve" ?

          Thanx again for kind support !
          Last edited by yamaha-115-96; 06-19-2012, 09:09 PM. Reason: Additional info on overheating
          Yamaha 2 stroke, -96, 115hp


          • #6
            I have read that spark plug wires being disconnected and not having a place to spark to or bad coils can cause voltage spikes that damage capacitors in CDI, but I have no proof to that.

            Poppet (PRV) sticking open can cause low RPM overheat, but higher RPMs should fill motor with water for proper cooling


            • #7
              Thanx for reply !

              What I will do is this:

              1. Remove ALL of "oil electronics" and only keep the black ground and the red wire (from low engine oil tank sensor. I suppose it is closing when oil is low. Have to test first.) going to pink termowire. Also remove the "diode" .

              2. Retest ignition coils and continuity of black/white wires (CDI to ignition coils) and check they haven't corroded to ground. When they removed the cylinder heads, the B/W wires (maybe corroded) could have been bent and being the straw that broke the camel's back, and in some way connected one or several B/W to ground ? They go in the harness together with black ground wires ? I think the B/W goes together at least with the pink (P) . When overheat-alarming, pink becomes a ground ? A weak spot if so !

              3. Put in new CDI-box

              4. Let you know the result

              Thanx again !
              Last edited by yamaha-115-96; 06-19-2012, 10:30 PM.
              Yamaha 2 stroke, -96, 115hp


              • #8

                To thank you all of you that have taken time to write down and post your experiences, I want to tell what was the final result of my efforts.

                The "project" expanded as I ventured into the engine.

                1. I discovered that the spark plug cap of the upper left cylinder lost connection intermittently. The cap is of the resistance type. I forced "resistor" out of the rubber protection, after having lubricated the surfaces between the resistor and the rubber.

                It is a "bakelite" enclosed component with the screw in one end and the loop for the spark plug in the other end. It was also rusty.

                I hypothesised that the overheating of the cylinders could have been the trigger for this rusting and finally broken connection. Sea-corrosion is said to need three components: humidity, heat, salt

                The more heat, the more catalysing of the oxidisation.

                With the upper right (starboard) cylinder, being named 1 (one), upper left 2 (two), lower right 3 (three) and lower left 4 (four)

                I found the deterioration of the spark plug caps, following the same pattern as a dark to light brown discolouring of the spark plug's isolator. This order also seems to follow the cooling of the four cylinders: from worst to best: 2 - 3 - 1 - 4

                Plug cap 4, was the only one having perfect values.

                It seems left cylinder bank is slightly worse cooled than right side and lower cylinders slightly better cooled than upper. The latter not being a surprise as the cooling water comes in from below and raises upwards.

                It was probably intermittent abrupt break of connection in resistor plug 2, that caused a back flow of currency into the CDI-box, "chocking" it some x times, and finally kill the box totally. I put a new box in from CDI Electronics: The World's Leading Ignition Spe******ts ::: 1-800-467-3371

                2. This finding in point 1. made me realise that the "cooling repair" of the cylinder heads, made at the authorised Yamaha workshop, wasn't sufficient.

                This led me to venture into a full cooling system inspection and possible refurbishing.

                I started with the potentially most difficult part, the exhaust cooling lid (the one on which the ignition coils sit), which according to many shouldn't be touched because likely 1-2-3 bolts would break due to corrosion. I dismantled the coils, applied paraffin to the bolts and gave each one a good heating (YOU MUST BE VERY CAREFUL TO HAVE EMPTIED ALL GASOLINE FIRST !!!). That treatment supposedly expands the bolts some "nanometer" and then retract them, at the same time as paraffin is "sucked in", freeing the corrosive/galvanic contact between the steel bolts and the aluminium lid.

                I dismantled it, found blocked 3mm holes and some corrosion, which I polished away and then painted the surface with primer and colour.

                The big "surprise" was the cooling lids over the cylinders. They were totally covered with a 1-2mm egg shell like material, especially over the cylinders and most on the left (port side) cylinder bank. Some "holes" were totally blocked, some partially. The Yamaha workshop didn't seem to have touched this area at all, but only ripped out the thermostats !!!

                NOW IF the thermostats would have been a problem (which I don't know), then the "open" flow to the top-lid, of water at higher speed, wouldn't have helped anyway!!!

                WHY? Because the crucial point was the heat transfer from cylinder metal to cooling water, was isolated by "egg shell" albeit there was no female bird "brooding" over the shell. The "egg insulation" was as biggest over the area covering the thermo-sensors themselves !! They must have become really hot.

                The simplest refurbishing would probably have been to give the surfaces a good blow with a sand-blasting gun, protecting sensitive areas first, now the time consuming scraping and sandpapering became my method.

                3. The misconnection of the trim-sensor and the oil unit cable (see earlier posts), didn't probably cause any big harm, but the technician probably got a sudden death whilst test driving, after having ripped the spark plug caps at the "refurbishing", causing the final death of the cap, and thinking he fixed the problem by connecting the two harnesses, that he thought had a perfect "physical fit". The engine randomly started again, because the corroded spark plug randomly reconnected !!

                Had he/she at this moment realised what was wrong, I wouldn't have had this costly purchase of a new CDI-box

                4. As we only use the "on engine oil tank", I rebuilt the harness and ripped out the oil unit and its cables, leaving the yellow "only-ignition-on (+) " cable from remote control as a stump. I have now put a 5 litre transparent oil bottle in the engine bay of the boat, where the top of the 5 litre oil level is at the same level as top oil in on-engine tank (at most critical tilt position). The two tanks are connected with the simple oil hose and working as two communicating bowls. The oil level is easily read on the big oil tank, and oil is easily replenished without having to go into the depth of the boat.

                5. The engine is now running smoothly with NO overheating alarm at WOT. The low oil warning in on-engine tank still gets its red + supply from the thermo-alarm-pink-cable and its ground supply from a new black wire to ground.

                6. Whilst ripping out most of the engine, I also found a NEW issue. Behind the starter motor and the starter relay, are going some oil cables. They are connected and secured by 4 steel clips. NOW it turned out these clips connected the starter motor case and the relay to the engine block, causing serious corrosion of all three components. I had to scrape, polish and paint all of it. Just a season or more and the components would have been destroyed. NOW the clips are isolated by sturdy high heat resistant plastic tubes.

                7. The rectifier which I thought was broke, seems to work !! It turned out the manual I had, had the readings of a three phase "alternator" , needing a 6-diode bridge rectifier, whilst my Yamaha with same year model and Hp and else, had a one-phase coil with a 4-diode rectifier. When I got a testing diagram of such a one, it turned out to be OK !!

                8. The only and NEW problem is that I have heard a humming/spinning sound under the cowling on one occasion and found it was the start motor spinning with the flywheel ! Either the lengthy winter stay on land has made the "recoiling mechanism" rusty OR there has been created some intermittent connection to yellow, green? or red cable to the brown (solenoid), that occasionally spins up the starter into the flywheel cogs whilst running ??

                9. FINAL POINT: Blocking (and corrosion) of cooling conduits in brackish Baltic Sea water seems to have two/three main causes:

                a) Heat deposition of microscopic calcium (lime) particles* on the hottest parts of the cooling system (over the cylinder heads) when steaming off of water at stopping the engine.

                *) stemming from "sea tulips"

                b) Growth of "sea tulips" on under water surfaces (The marina put rules into place two years ago that you can't tilt up the engine at the "parking place" , because the tip of the lower unit can scratch boats passing by)

                c) "Steaming off" of salt that deposits in corners and low places in crystalline form, NOT causing blockage in itself, but adding the third ingredient for corrosion, breaking down the protective coating and then building up blocking "rust", but also giving better attachment of the lime particles.

                IN THE BALTIC SEA where habit is to have the boat on water all the season and only being brought up to land over winter, the following advice to avoid my problems would be:

                a) Run the engine warm, on land with sweat water, at least 20-30 minutes when winterising (the lime dissolving effect of this advice I have not been able to confirm, because I haven't yet found scientific studies on it, but wouldn't hurt to do)

                b) IF forced by marina or else to have engine down, do ALWAYS dismantle the lower unit (10 bolts and opening the impeller not needed every year) and scrape all "sea tulips" off from the water supply tube, with a plastic or wooden scraper.

                c) Unscrew and ohm-test every spark plug cap, every season. Try to seal the cap both on the cable and spark plug side with dielectric fat/oil.

                Last edited by yamaha-115-96; 07-14-2012, 01:30 AM.
                Yamaha 2 stroke, -96, 115hp