Causes of weak spark on Tohatsu 18HP 2-stroke?

[32bit.flannel]

So I'm familiar with troubleshooting NO spark, but I don't quite know what to think about figuring out what could be causing a WEAK spark? I've done a good bit of googling but haven't found any decisive answers yet. The motor seems to idle and run just fine, so far having never missed a beat (though I don't yet have much over an hour's time on the water with it). Basically there is no real obvious sign of any problem, just that when I pull the (brand new) plugs, ground the strap and yank the cord I get a very very very weak looking spark. Even in the shade. This is the case with both cylinders, on a CDI motor with single coil. Is it typical for this motor (M18C2) to just have a weak looking spark when being tested like that, and it really picks up once you give it revs? I can't imagine such a weak spark could consistently pop the mix under pressure at high revs. And I don't think I have any low compression issues that would facilitate combustion from weak spark...cold motor with both plugs out gave me right about 90PSI in both holes. It could very well be one of those "if it ain't broke don't fix it" things, but I'd feel better knowing that I have the best spark I can get before relying on this thing out on the water. Thoughts from the pros?

Thanks,

Nick

 

[Sea Rider]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

You need a spark tester to test ignition coils output condition, if engine is working ok, what's the problem ? If not, you just have exciter, ignition coils or CD electrical related issues...

Happy Boating

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

...if enige is working ok, what's the problem ?

Yeah I know, that's what I was thinking too but still I can't help but to wonder that it isn't right for there to be such a weak spark.

 

[TOHATSU GURU]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

It should be a bright blue spark that is strong enough to put a hurtin on ya.

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

It should be a bright blue spark that is strong enough to put a hurtin on ya.

Thanks Guru, that's pretty much what I needed to know for now. I'm going to check all the wires, polish up the ground connections and sacrifice a crappie to the Spark Gods in hopes that I can avoid having to buy some expensive and hard to find ignition part.

 

[Sea Rider]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

If all electrical issues are ok, one thing that works miracles (sometimes depending on wire end condition) is to cut both ignition coil wires 5 mm at wire ends (where cap is screwed to) this will give new wire portions to screw caps on, if caps are too old, replace both for new ones.

Happy Boating

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

It should be a bright blue spark that is strong enough to put a hurtin on ya.

Sea Rider: That's a damn good idea, but turns out I didn't even get that far. Guru wins. I was about to pull off the flywheel to give everything a once-over but decided to first give the cord a few rips and make sure spark still looked poor (since it ran so well last weekend, after I had noticed the weak spark). The top plug looked _GREAT_ this time, so then I pulled the bottom and held them both up to the block while my father pulled...and I quickly became the path of least resistance. It sure did put a hurtin' on me! Bright blue ticking sparks and all, so on that note I'm saying case closed. Thanks again guys.

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Meh. I think the answer to this riddle just made itself crystal clear.

We were getting ready to head out fishing tomorrow and I thought I'd hook up the muffs and give a few yanks just to make sure she started up (I still don't trust the motor yet). THANK GOD I did because the damn spark is gone, and had I driven the hour+ to our fishing hole and discovered it there I might have tossed it into the lake. Poof, just like that..no spark! I ran it not a week ago and it was great, and just the other night I gave it a few yanks and it kicked over a couple revs, yet now I have nothing.

Long story short this is the first time that I can say with 100% certainty that I have no spark at all. My troubleshooting leads me to the coil. I hooked up a test light to the trigger wire from the CD to the coil and it was blinking as we pulled the cord, yet I get no zero spark. I then remembered what Sea Raider had last suggested, with cutting down the plug wire a bit, and that still had no effect. And to think I just got a new prop for the damn thing

Does anybody know where I can find a new coil, a used coil, and magical midget who can sit inside the hood and provide spark...or even suggest another model's coil that might interchange? So far I am finding nothing for P/N 362-06050-0, but I can't help but to wonder if one of these may not interchange:

http://cgi.ebay.com/ebaymotors/Niss...905665QQ_trksidZp5197Q2em7QQitemZ190509815736

http://www.marinepartssource.com/ne...&mcat3=&category=&mfgcategory=&mfgno=119-2400

I know looks don't mean much and P/Ns that are off by just one digit aren't really the same at all...but I'm kinda stuck grasping at straws on this one so if anybody has any thoughts please let me know.

Thanks again guys,

Nick

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

In my tired stuper last night my searching abilities were not quite all there. I looked again this morning and found a post where pvanv gave the following info:

"
And the ignition coil (362060500 is superceded to 3M3060481M) is also available:
3M3060481M IGNITION COIL W/RESISTANCE $43.73
"

Here's a link to that just for reference:

http://forums.iboats.com/showthread.php?t=457374&page=1

Meh. I think the answer to this riddle just made itself crystal clear.

We were getting ready to head out fishing tomorrow and I thought I'd hook up the muffs and give a few yanks just to make sure she started up (I still don't trust the motor yet). THANK GOD I did because the damn spark is gone, and had I driven the hour+ to our fishing hole and discovered it there I might have tossed it into the lake. Poof, just like that..no spark! I ran it not a week ago and it was great, and just the other night I gave it a few yanks and it kicked over a couple revs, yet now I have nothing.

Long story short this is the first time that I can say with 100% certainty that I have no spark at all. My troubleshooting leads me to the coil. I hooked up a test light to the trigger wire from the CD to the coil and it was blinking as we pulled the cord, yet I get no zero spark. I then remembered what Sea Raider had last suggested, with cutting down the plug wire a bit, and that still had no effect. And to think I just got a new prop for the damn thing

Does anybody know where I can find a new coil, a used coil, and magical midget who can sit inside the hood and provide spark...or even suggest another model's coil that might interchange? So far I am finding nothing for P/N 362-06050-0, but I can't help but to wonder if one of these may not interchange:

http://cgi.ebay.com/ebaymotors/Niss...905665QQ_trksidZp5197Q2em7QQitemZ190509815736

http://www.marinepartssource.com/ne...&mcat3=&category=&mfgcategory=&mfgno=119-2400

I know looks don't mean much and P/Ns that are off by just one digit aren't really the same at all...but I'm kinda stuck grasping at straws on this one so if anybody has any thoughts please let me know.

Thanks again guys,

Nick

 

[pvanv]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

That part is still available. The 2011 listing is: 3M3060481M IGNITION COIL W/RESISTANCE $45.48.

BUT... Before you just go buying parts and bolting them on... without testing to determine the problem... grab your copy of the Factory service manual, Part # 003-21035-1 $44.17, (available from any dealer, including me), drag out your trusty, decent-quality analog ohm meter, and diagnose the issue properly. Otherwise, you could swap out coil, CD, exciter, and possibly the kill switch, before actually getting to the root of the problem. Yes, "part-swapping" would ultimately fix the problem, but it is the slowest, most expensive way to service an outboard.

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

That part is still available. The 2011 listing is: 3M3060481M IGNITION COIL W/RESISTANCE $45.48.

BUT... Before you just go buying parts and bolting them on... without testing to determine the problem... grab your copy of the Factory service manual, Part # 003-21035-1 $44.17, (available from any dealer, including me), drag out your trusty, decent-quality analog ohm meter, and diagnose the issue properly. Otherwise, you could swap out coil, CD, exciter, and possibly the kill switch, before actually getting to the root of the problem. Yes, "part-swapping" would ultimately fix the problem, but it is the slowest, most expensive way to service an outboard.

Thank you for the wise words, pvanv. I orded the coil already, it was about the cost of a service manual actually, and if that doesn't work ill do more *proper* troubleshooting before dumping $200-ish bucks into a CDI. Ill keep everyone posted, even if just for posterity.

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Whelp...what a trip. I had ordered the coil from www.nissantohatsupartsstore.com (aka SILVERHAWK MARINE N.E.) and after SEVENTEEN days of "it will ship in 2-3 days" or "we are still waiting to get the part from Tohatsu" and "We had to order it from Texas and shipping is backed up"...I finally wrote a little love letter to which they promptly canceled my order and refunded my money. Not very communicative folks to work with, at all, would not recommend.

I then did what I should have done in the first place and ordered from Dowd Auto & Marine Supply, they are local Federated store, and within two days they had my part, and it was only $10 more than the first place would have been. Funny part is they ordered theirs from Texas too...

So I get the coil in the motor and I still have NO SPARK! Unhappy camper, I was. My dad and I started messing around with the test light and found the output from the exciter coil was WAY brighter than what the CD's wire to the primary coil was. This made me think the CD output should be at least as brilliant as the Exciter, but the CDI's output was about the same as the Trigger coil's output (in terms of brightness...Our multimeter doesn't refresh quickly enough to present good AC data). I then start to wonder if the ground wire from the CDI to the Magneto is somehow the problem, so I jump a wire from the same ground point as the CDI and primary coil onto the black wire, then reconnect the harness. BAM I have spark! Not a super great spark, but at least as much as I had ever gotten out of it. Then I remove the ghetto ground, reconnect the harness...and I still have spark. Better spark. Now I had checked the harness over already in search of corroded contacts (these looked brand-spankin-new), but I did NOT pay attention to the female ends being very 'loose', for lack of better term. I pinched the female connectors tighter, run some sand paper through them just for thoroughness, reconnect the harness and put everything back to the way I found it and I now have the best spark I have ever seen from this motor. It starts and idles like a champ, and tomorrow I'm getting out and will get to see if she's any better at WOT.

This also makes me realize that my original coil is likely still good, and pvanv's wisdom should not be glossed over (not that I meant to).

Pvanv: If you were to suggest a ohm meter for future troubleshooting what one would that be? I'm starting to see how digital may not be the tool for the job in these type of electronics.

 

[TOHATSU GURU]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Analog meter...And no factory service manual equals waste of time and money.

 

[pvanv]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Yes. You must use an analog meter. Preferably one with DVA (peak pulse) capability. Tohatsu sells an Electronics Specialties unit, which we use in our shop. Part# 99998D530M $124.32. Suitable for all Tohatsu/Nissan electrical testing. There are also good analog meters available under brands such as Triplett. You cannot use an ohmmeter that runs on more than a 3v battery, or you risk blowing the unit under test. IE, you can cook a CD box pretty easily.

Knowledge is power... and the Factory service manual has a lot of knowledge in it... empowering the technician.

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Thanks pvanv. I think what I have is the factory service manual, it's an 8x11-ish white booklet, maybe 3/8" thick, with blue text/graphics of engines on the front.

One other random question: Does this coil fire both plugs on each plugs' power stroke? If so am I correct in assuming it doesn't matter which wire goes to which plug? I'm a four-stroke small-block guy so this seems odd to me and made me curious.

 

[pvanv]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Any 2-cyl Tohatsu OB with a siamese coil (including 2- and 4-strokes) fires both plugs at the same time. This technically results in one "wasted" spark, but greatly simplifies the entire ignition system.

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

It's back *headdesk*. Was about to head out fishing Friday morning and when I gave it a couple tugs before we left (because I still don't trust it) the damn thing had lost it's spark yet again. Checked the connector that I thought might have been bad but no luck (I went so far as to cut off the three-prong plug and connect the wires directly). I had just run it for the day the Saturday prior and it ran great, so I have no clues.

The manual I have is the Shop Manual for M18C/350A, but mine is technically a M18C2/#350A so does that matter? I followed the testing outlined for the Kokusan Denki CD and I don't think I correctly understand the results it was looking for. I am going to provide a chart of my outputs and humbly request some assistance in determining if this box is hosed or not:



Just to recap: This started as an intermittent weak spark, which was seemingly fixed after replacing the coil and tightening a connector, but is now back again. Worked great a week ago, and several times prior to that week, before simply having no spark yet again this weekend. No external factors that I can identify to cause the failure. Right now I have zero spark. I also do now have a 1.5v analog multimeter so if there is any other worthwhile testing that should be done I am now able. If it's not the CD, and the coil is just a few weeks old...could something in the magneto just randomly fail like this? I understand what the magneto does and generally how it goes about doing so, but I don't have enough experience with them to identify what could fail to cause these conditions to be intermittent (unless maybe a busted coil wire?), so any other insight is appreciated.

Thanks again guys

 

[pvanv]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Did you also test the pickup coils (trigger and exciter) that reside inside the flywheel? When the malfunction is happening?

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Yes I did and I want to recall that the exciter was at 300 Ohms while the trigger was about 30 Ohms. I don't have my numbers in front of me right now so let me verify that before we call it truth.

 

[32bit.flannel]

Re: Causes of weak spark on Tohatsu 18HP 2-stroke?

Yes I did and I want to recall that the exciter was at 300 Ohms while the trigger was about 30 Ohms. I don't have my numbers in front of me right now so let me verify that before we call it truth.

Good thing I double checked...295-300 for the exciter and 60 for the trigger.