70TLRS CDI Ignition Coil Wire Identification

[MY70TLRS]

Hi Folks,

I recently removed all the electrics including the 3 coils and CDI unit from a 1994 Yamaha 70hp 2 Stroke outboard so I could overhaul the powerhead and in haste I forgot to label the wires from the CDI to the coils with the cylinder numbers. I've now realised that all three wires are black/white colour. So my question is, what is the simplest way to determine which of the three black/white wires belong to each of the three cylinders i.e. which goes to the coil for cylinder #1, which goes to the coil for #2 and which goes to #3?

Any assistance would be very much appreciated.

[boscoe99]

Easiest way would be to look at the wiring diagram in your service manual and simply connect the three coils according to what the SM depicts.

[99yam40]

trace the wires back to the connector at CDI, the colors change at that point, and you should be able to find out what cylinders those feed.

I would think the wire lengths should only fit one way

[boscoe99]

[99yam40]

well that blows my theory on this.


at least My C40 has what I said.(a 3 wire connector where the colors change)

probably could use a meter to see which wire it coming off the top, middle and bottom if you can get to the CDI connectors

[boscoe99]

Hope that I did not offend him with my comments. Just trying to impart some edumacationi.

[99yam40]

I think a lot of people find a bunch of web sits to post questions on, but do not come back to check for answers very often

[MY70TLRS]

Gents,

Apologies for the delayed response, I'm posting from Australia so bit of time zone lag. Thanks for you're responses I appreciate all your thoughts. Unfortunately all three wires from the CDI are black/white (no colour change) and are not routed so that you can see any order i.e not 2D like a wiring diagram, rather just exiting the CDI box in a soft round conduit. I'm reluctant to try and open the CDI box as It appears to be a sealed unit. I would have thought that others would have had the same issue when changing out the CDI box if like me they were silly enough not to label the wires?Maybe no one else is that silly

[zenoahphobic]

I imagine you can check with a multimeter by rotating the engine by hand to see which "pulse" corresponds to which cylinders. No need to know firing order as each fires every TDC (just a couple of degrees before). Or you could randomly connect and determine with the plugs out to see which plug fires and determine the cylinder, and then rotate the connections if required until they all match. All is not lost by not labelling these wires!

[zenoahphobic]

To clarify, start with No1 (top cylinder) and flywheel TDC timing mark, connect voltmeter (AC 200 volt ?) to an output wire from the ECU, turn on ignition, flick by hands the flywheel backwards and forwards over the mark alternating the voltmeter connection till you find the wire that pulses. Then move crank so that No2 is at TDC, determine this by using a soft stick or pencil down the plug hole, then mark with pencil on flywheel and do the same flicking about this point till one of the two remaining wires gives some reading.
That's just two steps. You may mark No3 and do the same just to verify that it pulses at its corresponding TDC (being 120degrees apart between cylinders) to be sure you have identified the correct corresponding wires.
Hard to believe wires aren't identified in someway; how was it assembled new at the factory?

[MY70TLRS]

Thanks for the suggestion Zenoaphobic I will give that a try. The service manual suggests that #2 will not fire below 500 rpm but if I can identify #1 using your technique and identify #2 due to no spark then #3 cant hide. I've just finished a complete rebuild of the powerhead (first ever engine rebuild) and I want to get the firing order right for the first start so your assistance is appreciated.

[donsmarine]

maybe the top one on cdi box goes to top cyl, if there is a top

[TownsendsFJR1300]

To add to the above, and the wiring diagram, below is a pic of your CDI.
I circled what is likely the "hot" wires to the coils

Do they come of out of the CDI initially, (perhaps following the diagram)?

IE, from top to bottom, cylinder #1 down to #2, then to #3?






The link to your CDI: https://www.boats.net/catalog/yamaha...s/electrical-1






.

[MY70TLRS]

Hi TownsendsFJR1300,

Unfortunately I cant tell which wire is on top as the three wires exit the CDI box in a soft round conduit. If I could open the box the perhaps I'd find a buss bar inside that might help but I don't want to do that as it appears to be sealed. I'll run with zenoephobic's logic as I think that's going to be the best way to determine the firing order without compromising any other components. If anyone has experienced this problem before please feel free to comment. I cant get back to the rebuild until this weekend. Thanks

[99yam40]

I would think that a timing light would point you to the proper wires.

before hooking up any fuel, hook up the coils any way you want and then hook up a timing light and spin the motor over
from what you said #2 should not show any spark
#1 should indicate properly on the timing mark for #1.
#3 will be at a different point on the flywheel


if the flywheel is not already marked for TDC on #2 and #3 you could mark them yourself if you want