225TXRP plug wires?

[carboncow]

Can one replace the plug wires to the CDI on a 1991 225TXRP?

We have been water testing our older engine who has been getting much love lately. It jumps out of the hole and wants to scream but as it middle to upper RPM it seems to have a intermittent miss that reminds us of a misfire.

My knowledge of 2 cycle outboard is terrible and trying to apply car "ideas" to the project may be wrong but it seems to me in our desire to do most things right we should be replacing plugs too.

Thoughts?

[TownsendsFJR1300]

If you have a clip over wire style, timing light, I would clip it over each wire, one at a tome of course.

You'll need a helper to look at the light when the engine is acting up and see if a particular wire is NOT firing as much as the others.. Should be pretty obvious.

[TownsendsFJR1300]

If you have a clip over wire style, timing light, I would clip it over each wire, one at a time of course.

You'll need a helper to look at the light when the engine is acting up and see if a particular wire is NOT firing as much as the others.. Should be pretty obvious.

Here's a pic/link of the ignition system:

1991 225TXRP Yamaha Outboard ELECTRIC PARTS 2 Diagram and Parts

It appears the coil and wire are one, the spark plug cap is separate. *You may also want to check the spark plug cap @ the wire end for any arcing, etc. They should be snug. The caps should screw on (regular thread) to the wire.

A look at the spark plugs may also help pin point what cylinder is acting up to narrow down the issue...

[carboncow]

Thanks good info. For whatever reason I looked over the fact that each unit was separate. So these are like little "direct ignition" units.

Can a tech put the engine on a Yamaha computer to see which are failing too. I would assume they would fail at the higher RPM regardless of load. Or is this engine to old for fancy computers?

EDIT: I make these comments to for future people looking for similar concerns. We'll report back findings. Note, we did note that when the engine got splashed (while troubleshooting) the misfire got worse...I think the cap/boot and arc'ing is a great possibility. They also look to have grounds coming off those capacitors (to the block) that we'll take off and clean.

[TownsendsFJR1300]

Thanks good info. For whatever reason I looked over the fact that each unit was separate. So these are like little "direct ignition" units.

Can a tech put the engine on a Yamaha computer to see which are failing too. I would assume they would fail at the higher RPM regardless of load. Or is this engine to old for fancy computers?

EDIT: I make these comments to for future people looking for similar concerns. We'll report back findings. Note, we did note that when the engine got splashed (while troubleshooting) the misfire got worse...I think the cap/boot and arc'ing is a great possibility. They also look to have grounds coming off those capacitors (to the block) that we'll take off and clean.

As you know, a bad ground will cause all kinds of issues. Just looking at it doesn't count. It needs to be pulled and remove that aluminum powder dust you know will be under there...

My 4 cylinder has two coils, yours obviously has 6, one for each cylinder. If it can be hooked up to a computer, I don't know. A shop manual (or someone here should know) should show how to check each coil.

With the "splash" you mention, I would crank that engine up(with muffs or in the water) in the darkest spot you can find and look for any sparking/arking, etc.

If none found, duplicate those conditions with a spray bottle with water. Just a little at a time.. Once you get to one section, spray and if $hit happens, your definitly narrowing it down. Bad ground, bad coil shorting out, bad wire, etc..

The spark plug caps are a known issue on a Yamaha motorcycle forum I frequent. The caps loosen up with the wire, get some arcing going, engine runs rough, etc. The fix is to cut off 1/4 of wire(the arced, worn wire), then screw the cap back on making sure your in the middle of the main conductor until snug..

BTW, on that link, you can click for other area's of the engine if need be..

Please post what you find, etc.. Good luck..

[carboncow]

Do you know much about what I'm reading is called "the trigger" with timing/coils?

I'm relaying this via my buddy who is testing the engine today...while I'm home with family so bear with me.

He mentioned the rpms being off on our new digital tach. It can be set to 6 or 12. I thought it was 12 but we set it to 6 as 12 showed no signal at first...we could have got this wrong.

He noted today that he felt the rpms were very high on the tach (from reality) and said they may have been even twice as high. Would this mean we got the tach setting wrong or...

I saw a few youtube videos discussing this (see: https://www.youtube.com/watch?v=TWZ6JoqBaMk) and was wondering what the trigger is as he talks about it firing to much for each cycle...again bad coil or computer telling it to fire?

I'm sure it's the wire, grounds or caps/connectors but I'm very curious to what this guy (and others) are talking about with "trigger".

[TownsendsFJR1300]

Do you know much about what I'm reading is called "the trigger" with timing/coils?

I'm relaying this via my buddy who is testing the engine today...while I'm home with family so bear with me.

He mentioned the rpms being off on our new digital tach. It can be set to 6 or 12. I thought it was 12 but we set it to 6 as 12 showed no signal at first...we could have got this wrong.

He noted today that he felt the rpms were very high on the tach (from reality) and said they may have been even twice as high. Would this mean we got the tach setting wrong or...

I saw a few youtube videos discussing this (see: https://www.youtube.com/watch?v=TWZ6JoqBaMk) and was wondering what the trigger is as he talks about it firing to much for each cycle...again bad coil or computer telling it to fire?

I'm sure it's the wire, grounds or caps/connectors but I'm very curious to what this guy (and others) are talking about with "trigger".

I'm not familiar with the "trigger" to speak of, especially on the Merc, so I can't say. Probably an electronic pick up to read the flywheel and tell the computer when to light up the spark plugs I would guess.. Same as "points" on the older cars before electronic ignition.

Every conventional engine has to have some sort of trigger (maybe not the right word) to tell the computer to signal coil #1 to fire, etc..

Re the tach. Do a serach here on the forum, it has been brought up before for the correct setting (the post had the tach reading too low). To my knowledge, that setting for the tach, even if incorrect won't make the engine act up, just the tach reading wrong. In general, WOT should be towards the top end between 5,000 and 6,000 RPM's.

Something I thought about later as well to check. With the age of that engine and the water spray issue, I would (besides the previous post), pull every electronic connector apart and inspect for corrosion (mostly green).

If your engine has the smaller connectors prevelent today, their much more affected if corrosion is in a connector(less surface area). It doesn't take one bad small connection (or pulled wire from a connector) to have issues. Checking the main, large plug to ECU (or computer) would be time well invested.

Any, connector marine, motorcycle, bulb, I pull apart, once clean or already clean, gets a light coating of Di-lectric grease. This about gaurentees NO MORE issues with corrosion getting into that connector.

As a side note, my old, 04, Yamaha FJR1300 motorcycle, (while still under warranty) was having some intermediate misfiring. Spent most of the day at the dealership, they spoke with Yamaha in California, could NOT figure it out...

Went to my FJR forum (extremly knowledgable folks, like here). For that year, other folks were having the same issue. They found a connector under the fuel tank, would pick up moisture and the contacts turn green. I pulled my tank, found that connector, sure as $hit, green inside... Cleaned it all out, di-lectric grease installed, re-installed the tank. Fired it up and I knew immediatly it was fixed. A test ride confirmed it repaired. Never had another issue with it, NEVER... One little connector Yamaha wasn't aware of and couldn't fix/find...

[rodbolt17]

merc and OMC called them trigger coils.
Yamaha and some others call them pulser coils.
both do the same thing.

as the stator charge coil voltage is rectified and stored in a set of capacitors inside the CDI unit(see why its called a CDI ign system) the caps are sitting there with about 150V potential difference to ground.
just like a battery,charged and ready.

the capacitor discharge path is through an SCR.
this SCR is triggered ON by a pulser coil input signal.
maybe 1.5-15V.
once turned ON the SCR allows the cap to discharge through the ign coil primary windings.
as current falls below the SCR threshold the SCR turns off and the cap charges again.
this happens very rapidly and as the current through the ign coil fails the magnetic field it generated collapse acrossed the secondary windings generating anywhere from 7-10 KV on a normal running engine.
that's 7-10 thousand volts.

its the current through the primary windings that sets up the magnetic field.
its the sudden stoppage of current flow that causes the rapid collapse of this field and induces a voltage in the secondary windings.

points and TCI systems use either a mechanical switch,points, or a transistor,TCI, to turn OFF the current to the coil primary.

easiest way to test your setup is watch the CDI output voltage on an analog meter capeable of reading PEAK voltage.
true RMS is NOT peak.
I use either a CD 77 from stevens or my mercury equivalent purchased from sierra.
last I looked the sierra meter was about 120 bucks and the last CD-77 I bought was about 270.
for a quick intermittent issue I don't use digital as its buffered and is to slow most the time to catch it.

[carboncow]

Thanks we do have some some good digital and analogs at work that do peak values...will check them out.

Where is it best to measure the CDI output and what peak voltages would we be looking for that confirm healthy operation?

Thanks for all the advanced tech...it is very helpful to the non technician although it takes a few reads!

[rodbolt17]

measuring point is at the bullet connector between the CDI and the coil.
should see about 150-200V peak.
your service manual will have the minimum specs.

[99yam40]

Just because the meter has a peak hold setting it is still not the correct meter to take these readings unless it was designed for these ignition systems.

High dollar Fluke meters will not get it done by them selves, ask me how I know this.

Pick up a Dva adapter or make one to get the proper voltage readings to compare to service manual specs

[rodbolt17]

goes back to why I wont use a digital meter to hunt for intermittent fluctuations.
even with a DVA adapter some buffereing,time delay, occurs.
analog will catch it.
however analog is polarity sensitive so anticipate what your looking for,
some motors use BOTH sides of that 150+ ac sine wave and 1/2 the ign system will fire with a NEGATIVE voltage.
that 150+ potential to 0V can be positive or negative. the trons mostly don't care.
if you use a Kv tester this becomes rapidly apperant when it shifts from conventional to inverted.