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Magneto Check


Duski Don

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G'day from Down Under,

 

Carrying out normal (4000 RPM) checks on my '06 CTsw. 246 hours total VDO time of which approximately 90 hours in the last 5 months. It was a dealer demonstrater and only done 157 hours in the preceding 4 years.

 

No RPM drop on No2 whatsoever, then about 1500 drop and rough running on No1.

This got progressively worse on susequent tries after wiggling wires around, changing plugs etc. and eventually wouldn't run on No1 at all.

 

Have sent coils and capacitors?(black boxes)off to Oz Rotax agent for testing but would appreciate any feedback from Roger or anyone else who may have had similar experience.

 

Thanks,

Duski Don (Briggs)

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Hi Don,

 

That is quite a mag drop. You could have left the charging coils in place and tested them at the top by the ignition modules with an ohm meter. You definitely have a bad charging coil, broken wire or a bad module. The module could have been more or less tested on top by switching the A & B ignition module plugs from one to the other and see if the problem followed the module. My bet is it is either a broken wire, most likely on top of the engine or a bad ignition module. Broken wire first, module second. I would follow the two white ground wires that go under some of the coolant hose. This is an easy place to break a wire.

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Hi Don,

 

That is quite a mag drop. You could have left the charging coils in place and tested them at the top by the ignition modules with an ohm meter. You definitely have a bad charging coil, broken wire or a bad module. The module could have been more or less tested on top by switching the A & B ignition module plugs from one to the other and see if the problem followed the module. My bet is it is either a broken wire, most likely on top of the engine or a bad ignition module. Broken wire first, module second. I would follow the two white ground wires that go under some of the coolant hose. This is an easy place to break a wire.

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First of all I just have to say that I love ignition problems, why? Because most of the time they can be quickly diagnosed with some very basic systematic troubleshooting, I have to admit that I have spent some time over the years pulling my hair over ignition issues before I developed a full proof method for diagnosing faults.

 

General things to consider...

 

1) If one cylinder was not firing at all then when you do your mag drop at 4000rpm you can expect to see a 400-600rpm drop

2) If two cylinders were not firing at all then when you do your drop at 4000rpm you can expect a 900-1100rpm drop

 

Step 1) If you are getting a high mag drop (over 200rpm) you can pretty much rule out it being an issue with your ignition switch ground, in most cases ignition switch issues are never severe enough to cause more than a slight irratic running, 98% of the time ignition switch issues lead to a complete failure of one whole system. To clarify it's going to be one or the other.

 

Step 2) Try switching the black boxes, why? Because it takes all of about 15 min and it will almost immediately rule out the single most expensive part in the system.

 

Step 3) Return the black boxes to there original locations but before doing so, grab a small ice pick and disconnect the red wires coming into the rear of the engine. Then switch these wires a perform a test run. Ask your self does the problem switch sides? These wires are what sends the AC voltage developed by the stator on the rear of the engine to the black boxes to be directed to the spark plugs. If the problem switches sides then it is an issue with the stator ( check wire resistance to ground 3.2-4.5ohms) if the problem doesn't switch sides then the issue is "down stream " of the stator and is either in the black boxes ( which you have already ruled out) or in the secondary coils and plugs.

 

Step 4) After determining that the issue lies in the secondary coils then the next logical step is to check the resistance of both sides of the coils the primary side being fed by the black boxes ( 0.1-0.4ohms) then test the secondary.

 

Step 5) check your triggers, these are located on the back of the engine and tell the black boxes when to fire the spark, there are 4 of them that trigger a respective secondary coil, the resistance should be 220-250 ohms for the new style, these a rarely the problem unless there has been physical damage to them, they are also only replaceable as a set so as much as I would love to sell you a set please be sure that they are not working before ordering... Were trying to be mechanics not parts changers right?

 

Note: the secondary coil is suppose to be between 6.1-6.7 kohms, to get this reading rather than removing both spark plug caps, since this may hide your problem I would leave both caps connected and test from one cap to the other (1&2T...1&2B ...3&4T...3&4B) each cap is rated at 5kohms so your readings should be between 16.1-16.7k ohms the 0.1 ohm per foot of the spark plug cable should not be a factor.

 

After all these test have been performed you should of localized the problem to a specific component.

 

Common issues more or less in order..

 

1) loose spark plug caps!

2) Bad grounds ( look for corrosion on central grounding point on #1/3 intake manifold)

3) Bad charging coil, usually as a result of a loose cap or running the engine with out spark plus caps installed with mags on

4) ignition switch ( like I said usually only the case with either very slight mag drops or complete failure

5) charging wires there is a SB on older engines but in the case of most CTs it would most likely be related to physical damage ( shorted or nicked wire)

6) Black boxes ( rarely ever fail but when they do it's almost always related to heat under the cowling

7) Triggers, usually as a result of physical damage, be very suspicious of this if your engine has recently been removed

8) Timing.....oh wait!? It never changes ( this can pretty much be ruled out every time :-)

 

There you go...

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G'day from Oz,

 

Can anyone advise me on the following:

 

What relates to what with regard to No1 and No2 on the ignition /start switch?

 

IE: which black box (A or B) and when you you switch to No1 is this switching off No1 or No2?

 

(I'm getting a bit of conflicting advice from some local 'experts')

 

Duski Don

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G'day from Oz,

 

Can anyone advise me on the following:

 

What relates to what with regard to No1 and No2 on the ignition /start switch?

 

IE: which black box (A or B) and when you you switch to No1 is this switching off No1 or No2?

 

(I'm getting a bit of conflicting advice from some local 'experts')

 

Duski Don

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I would follow the two white ground wires that go under some of the coolant hose. This is an easy place to break a wire.

 

Well, strictly speaking, wouldn't a broken "P-Lead" (or CDI equivalent) lead to NO "mag" drop?

 

Unless, of course, that broken lead was grounding intermittently (a hard ground would result in the engine completely dying when the other "mag" was selected (because both would be grounded then).

 

Right?

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Hi Don,

 

If someone wired it right it would be switch position 1 for the "A" ignition and switch position 2 for the "B" ignition. Each ignition module controls a plug on each cylinder, so each module controls 4 plugs. The but part here is you can swap ignition module A-B from one to another on top of the engine connection or someone may not have put the right module to the right ignition position switch. These are easy to check so instead of listening to people just start the engine and see which plug is firing on ignition position 1. Then the other ignition module will be firing the other set. You only need to know one plug on because in the Heavy Maint. manual there is a diagram that shows which plugs are firing on which ignition module. "A" module is on top. You could determine this in about 5 minutes or less. Look at the firing chart in the maint manual first then find out, let's say which ignition module is firing number 1 cylinder. Compare it to the chart and your done.

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Just take this AC testing tool and hold it up by a plug and turn off one ignition and see if the test light goes out or stays lit. That's all there is to it. When you know which plugs are off on let's say ignition switch #1 then that's it. Now you know what module and switch position controls what. With this $12 AC tester you can track and check for any broken or poor connection on the plug wire AC producing circuit. Just hold it next to a wire and run it along the surface or up to a plug and watch the light to see if it flashes.

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post-3-035687100 1294696791_thumb.jpg

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Duski Don, I've just spent a couple of weeks getting to know my ignition circuits intimately, it's bad when a circuit diagram becomes your favourite bedtime reading ! anyway all issues with the engine have been resolved and it's silky smooth again. Roger is corect in saying that if wired properly that position 1 on the ignition swith is Box A and positon 2 is Box B.

However, Box A controls the sparks for cylinders 1 top, 2 top, 3 bottom, 4 bottom, whilst Box B controls the sparks for cylinders 1 bottom, 2 bottom, 3 top, 4 top.

Mac

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G'day Guys (and Girls),

 

This is the latest with the loss of one ignition circuit:

 

Black boxes and ignition coils checked by Oz Rotax distributor (Bert Flood) and all declared OK.

 

Local auto electrician (there aren't any aviation specialists in Narrogin WA) checks out wireing and switch and declares them all OK and doing what they're supposed to.

 

We switch plugs to black boxes but problem remains with switch in No1 position.

 

Cannot detect any OBVIOUS fault with two white wires that go under coolant hoses.

 

I will be contacting Bert Flood again tomorrow (Monday) but would welcome any feedback.

 

Duski Don

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Hi Don,

 

I still think when this is finally finished it will be a broken wire or a bad connection on a Molex plug pin that will be the cause. This acts like a total separation some where (1500 rpm drop) and not just a single component (300-800 rpm drop) because the rpm drop is too high. It is very rare to loose an ignition module. Loosing a single component ( i.e. ignition coil) next in rarity, but broken wires and loose pins in plugs is very common.

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  • 2 weeks later...

First of all I just have to say that I love ignition problems, why? Because most of the time they can be quickly diagnosed with some very basic systematic troubleshooting, I have to admit that I have spent some time over the years pulling my hair over ignition issues before I developed a full proof method for diagnosing faults.

 

General things to consider...

 

1) If one cylinder was not firing at all then when you do your mag drop at 4000rpm you can expect to see a 400-600rpm drop

2) If two cylinders were not firing at all then when you do your drop at 4000rpm you can expect a 900-1100rpm drop

 

Step 1) If you are getting a high mag drop (over 200rpm) you can pretty much rule out it being an issue with your ignition switch ground, in most cases ignition switch issues are never severe enough to cause more than a slight irratic running, 98% of the time ignition switch issues lead to a complete failure of one whole system. To clarify it's going to be one or the other.

 

Step 2) Try switching the black boxes, why? Because it takes all of about 15 min and it will almost immediately rule out the single most expensive part in the system.

 

Step 3) Return the black boxes to there original locations but before doing so, grab a small ice pick and disconnect the red wires coming into the rear of the engine. Then switch these wires a perform a test run. Ask your self does the problem switch sides? These wires are what sends the AC voltage developed by the stator on the rear of the engine to the black boxes to be directed to the spark plugs. If the problem switches sides then it is an issue with the stator ( check wire resistance to ground 3.2-4.5ohms) if the problem doesn't switch sides then the issue is "down stream " of the stator and is either in the black boxes ( which you have already ruled out) or in the secondary coils and plugs.

 

Step 4) After determining that the issue lies in the secondary coils then the next logical step is to check the resistance of both sides of the coils the primary side being fed by the black boxes ( 0.1-0.4ohms) then test the secondary.

 

Step 5) check your triggers, these are located on the back of the engine and tell the black boxes when to fire the spark, there are 4 of them that trigger a respective secondary coil, the resistance should be 220-250 ohms for the new style, these a rarely the problem unless there has been physical damage to them, they are also only replaceable as a set so as much as I would love to sell you a set please be sure that they are not working before ordering... Were trying to be mechanics not parts changers right?

 

Note: the secondary coil is suppose to be between 6.1-6.7 kohms, to get this reading rather than removing both spark plug caps, since this may hide your problem I would leave both caps connected and test from one cap to the other (1&2T...1&2B ...3&4T...3&4B) each cap is rated at 5kohms so your readings should be between 16.1-16.7k ohms the 0.1 ohm per foot of the spark plug cable should not be a factor.

 

After all these test have been performed you should of localized the problem to a specific component.

 

Common issues more or less in order..

 

1) loose spark plug caps!

2) Bad grounds ( look for corrosion on central grounding point on #1/3 intake manifold)

3) Bad charging coil, usually as a result of a loose cap or running the engine with out spark plus caps installed with mags on

4) ignition switch ( like I said usually only the case with either very slight mag drops or complete failure

5) charging wires there is a SB on older engines but in the case of most CTs it would most likely be related to physical damage ( shorted or nicked wire)

6) Black boxes ( rarely ever fail but when they do it's almost always related to heat under the cowling

7) Triggers, usually as a result of physical damage, be very suspicious of this if your engine has recently been removed

8) Timing.....oh wait!? It never changes ( this can pretty much be ruled out every time :-)

 

There you go...

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Thanks Jeremy,

 

Eliminated black boxes and coils and eventually worked out that the maybe the red wires "coming into the back of the engine" were the ones in the plugs into the black boxes.

Switched them and sure enough the problem switched from A to B circuit.

I note you advise the resistance should be checked.How do I go about this? (I have a multimeter but must confess don't know much about resistance measurement)

If the wire is broken or shorting and needs replacing how do I go about this? Will it require the engine to be lifted out?

 

Any advice would be much appreciated.

 

Regards,

Duski Don (Briggs)

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G'day from Down Under,

 

Finally tracked the problem to the A circuit red stator wire. It shows only 1.4 ohms resistance.

 

I assume I now have to lift the motor out to identify and rectify the problem.

 

Notwithstanding the Rotax manual etc would welcome any helpful hints on removing the propellor and motor and replacing all the hoses (might as well completely blow the budget while I'm at it)

 

Regards to all,

Duski Don (Briggs)

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  • 1 month later...

G'day All from Down Under,

 

Finally fixed my ignition problem.It was a (red) power wire shorting onto the braided wire sheath. This in turn due to the sheath being crushed betwen the top engine mount and ignition housing on the left hand side of the motor.I assume this was done during the fitout by FD and the insulation and internal protective ruptured, albeit very slightly, in due course. Might be worth having a bit of a close look at this power supply loom.

 

Duski Don (Briggs)

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  • 2 years later...

On our way back to Tn from Houston our "a" module, ignition switch position 1 decided to give up the ghost.

 

After 600 hours this seems like a premature failure and begs to ask the question. Do I have to purchase another duplicate switch from FD or is an acceptable aftermarket available?

 

On a personal note.

 

If this thread and CTFLIER group did not exist, I would have been stuck on the ground, about midnight, in the middle of no where land.

Thanks again to ALL that contribute to this group.

 

YOU ARE THE ONES THAT GOT ME HOME LAST NIGHT!

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Hi Chris,

 

600 hrs. Is premature, but not unheard of. I don't think you'll find an aftermarket. I know it's not what you want to hear. Even though your engine is out of warranty sometimes if you file a claim and state that you think it was premature they will help out on the part purchase price and it can be significant.

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