Yamaha 90A 2 Stroke - Anyone knowledgeable on coils?!

[markS]

Hi all,
I have a terrible intermittent 'no spark' issue. It can literally be sparking one minute and not the next.
Engine has been perfect for 10 years, then out on the water after 3 hours of chugging around it suddenly cut out and wouldn't restart.
It caused me and my kids to get stranded and towed in (thankfully) by a kind trawler! It was just turning dark when the failure happened, suffice to say it's not an experience I wish to repeat, so boat is grounded until resolved.

I have taken readings of the various relevant components (pulser coil, CDI, etc). But I am not too sure how to make sense of them as they don't correspond to the service manual I was using (trying my best to understand it!). The engine is mint, 2010 with under a hundred hours of use. All connections are spotless, no corrosion, and covered in a nice smear of vaseline as they have been for the past ten years of my ownership. It's had virtually no use with me until this year (no time, or no money, or both!)

I took readings of both the voltages (when cranking) and resistances of the various parts. I will paste them below, I am desperately hoping someone knows a lot more than me about these engines, and might be able to comment on whether anything can be learned from this data?
Thanks

CDI output - when cranking
#1 - 1.1 to 1.3Vac
#2 - 0 to 0.4Vac
#3 - 1.1 to 1.3Vac

Charge Coil
R-Br - 61Vac (12/13 Ohms)
R-L - 74Vac (200 Ohms)

Pulser Coil
0.7 to 1.1Vac (309 Ohms)

Lighting Coil
12.85Vac (1.2 Ohms (dropping))

Crank Sensor
2.65Vac (197 Ohms)

[neil.mccrirrick]

Can’t interpret your readings without a manual but I’d suspect coil if the readings are not the same.

However start simple. It’s electrical when did you last change the battery?

Are the leads tight?

If it’s intermittent first place is check all connections. After that check battery leads for breaking down. After that you are likely into a failed component eg coil breaking down

Hope that helps some

[markS]

They are all coils!

All simple stuff has been ruled out. Rock solid battery, soldered connections, clean terminals tight etc etc. Also ruled out kill switch and all the other usual suspects. I think we are down to components.

I have today managed to find resistance readings in the manual, didn't see them before but managed to make my keyboard make an OHMS SUMBOL in a digital search of the service manual, and hey presto, YAY!

Here is a direct link to page 28 (2-8) of the manual which shows all the correct resistances, time to start studying!

I found out last night how much these components cost, hundreds even just for a pi55y little pulser coil, so I have to check and check and check, can't afford to 'guess buy'!

[spartacus]

Just a thought, I assume the remote has start in gear protection? There should be a little microswitch in there. Relatively inexpensive and potentially could be the issue.

[A1an]

Originally Posted by spartacus

Just a thought, I assume the remote has start in gear protection? There should be a little microswitch in there. Relatively inexpensive and potentially could be the issue.

That shouldn’t cause it to cut out whilst running.



I had a similar issue with a Honda and it turned out to be the CDI unit throwing a hissy for no apparent reason.

[neil.mccrirrick]

When it cut out could you tell if you lost all cylinders? If it sounded like any cylinder was trying to fire check ignition coils.

If there was nothing check neutral and kill switch

[markS]

Thanks all, some good suggestions there. To answer:

When it cut out I am certain it was all three, no sparks on any cylinder. I am sure ignition coils are fine. I have learned a lot in past few days, hours of watching Dangar Marine type videos and reading threads on here and elsewhere. Was worth the time in long run I think, just hate being out on water and not really understanding my own engine. (even though "2 strokes don't go wrong", hahaha)

PROGRESS...:

CDI unit, Pulser Coil and Charging Coil are the three most likely suspects here.
CDI unit I can't test properly (i now know) until I get my DVA adapter (hopefully today). But I can test resistances of the pulser coil and the (2 coils inside the) Charging Coil.

Pulser book says should be 241-362 ohms. My reading is 309 so looks ok to me.
Charging coil - one coil should be 191-288 ohms and mine reads 200, good. But the other coil in it should be between 64-96 ohms, but mine reads 12 or 13 ohms.

Do we have a prime suspect?!

[beamishken]

With an intermittent fault I dont think the readings are very meaningful unless the fault is occurring at the time. I'm assuming the engine now starts & runs okay? Unless you can recreate the fault it will be difficult to pinpoint with any degree of accuracy.

[markS]

Thanks, that's a very good point.
It is failing now. No spark.
I bought a set of Laser spark plug lighter upper thingermejiggies off Scamazon. Those are staying connected so I shuold see some lights flashing if I do get a spark back. But no spark currently. Would be nice to see a spark so I could test while it is working but the Gods aren't shining on me on that score at the mo

[beamishken]

Originally Posted by markS

Thanks, that's a very good point.
It is failing now. No spark.
I bought a set of Laser spark plug lighter upper thingermejiggies off Scamazon. Those are staying connected so I shuold see some lights flashing if I do get a spark back. But no spark currently. Would be nice to see a spark so I could test while it is working but the Gods aren't shining on me on that score at the mo

Got a cdi here that lost a cylinder if you want to try it, obviously if it runs on two cylinders you know its the cdi. The fact you have a complete failure is a good thing usually easier to fix than an intermittent fault

[markS]

Wow, what a generous offer, that's extremely kind of you. I am hoping it isn't the CDI, but having that available would get rid of the need for "hope"!
So your one is faulty but has a known fault (only runs 2 cylinders). So if i swap mine out to that, and I get 2 cylinders running, my CDI is bad. Sounds like a great thing to have on the bench to try amongst the various other tests! Would you like to PM me to sort that so I can send you postage money etc?

PS - No, the problem I have appears to be VERY intermittent! It's just that it's in "bad mode" right now. I could go turn the key this afternoon and it could be sparking again! It's a nightmare! I have bought the spark plug tester lights so I can hopefully noticed if/when it sparks again, maybe it won't, maybe it will!

The trouble with this stuff is, everyone seems to say "well it can't be that because it's intermittent and that would just fail" about EVERY component I mention, CDI, pulser coil, charging coil.... all of em! Some people say "Never known a CDI to go wrong" which is as useful as a chocolate fireguard, even more so if i DO have a bad CDI!! So I have given up guessing and gathering amateur opinions (mine included ). It's now down to testing every component.

I can't test the CDI until tomorrow as the DVA didn't arrive today as hoped. But it would be very interesting to have a spare CDI I could test the outputs of, to compare to mine. Just to rule out my own testing equipment/process. If yours reads as per book (on 2), and mine doesn't, I would have more faith in my readings before taking out a mortgage for a new CDI!

Thanks again, very kind of you.

[Peter_C]

You would need a lab scope for more thorough testing. About all you can do is check inputs, and grounds, as there isn't much you can do for testing a "black box" itself. Using a replacement unit is about the only way. The tap and wiggle test is a valid test LOL

Have you taken an ohm's reading for the coils themselves?

[beamishken]

Is it the same?

[markS]

Originally Posted by Peter_C

You would need a lab scope for more thorough testing. About all you can do is check inputs, and grounds, as there isn't much you can do for testing a "black box" itself. Using a replacement unit is about the only way. The tap and wiggle test is a valid test LOL

Have you taken an ohm's reading for the coils themselves?

haha. Not sure i took resistance reading for coils, kind of ignoring them as i either have 3 sparks or none, but i will get readings tomorrow and post back. thanks

[markS]

Originally Posted by beamishken

Is it the same? Attachment 143507Attachment 143508

Certainly looks the same, incliuding wire colours, but not sure if that is reliable enough. I have never removed one (bit scary for me!) so I guess i need to remove it to check numbers on the back? Or maybe I can research it using diagrams online. My engine is 2010 model:



ha, i posted image but it's not showing for some reason. Its here: https://ibb.co/qsL4QtZ

[beamishken]

Theres nothing to be scared of removing one just pop off the timing rod & unplug the wires i think the 6ho in the plastic moulding is the relevant no if yours matches that then I think your okay

[markS]

I see. Thanks, Will have a bash tomorrow.

[beamishken]

Originally Posted by markS

I see. Thanks, Will have a bash tomorrow.

Should be able to see the no with it insitu but it may have a cable cover you'll need to remove to see it that one is mega expensive £500 ish but a 6h2 one which fits the 60/70 is available as a copy for about£80 looks almost identical too

[Peter_C]

Originally Posted by markS

haha. Not sure i took resistance reading for coils, kind of ignoring them as i either have 3 sparks or none, but i will get readings tomorrow and post back. thanks

Part of testing the coils is also testing their wiring. The coils could be considered the output side of the circuit. Test the input side of the circuit, and if all good replace the module. Then cross your fingers when you hit the key.

Complete failure of a component is far better than chasing an intermittent problem.

[markS]

Originally Posted by Peter_C

Part of testing the coils is also testing their wiring. The coils could be considered the output side of the circuit. Test the input side of the circuit, and if all good replace the module. Then cross your fingers when you hit the key.

Complete failure of a component is far better than chasing an intermittent problem.

Thanks. I assume you mean the pulser/charge coils, not ignition coils, as those have been ruled out. I am not sure how to test the input side of those connectors, any tips?!