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Ignition system problem. Need help!

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Ignition system problem. Need help!

Postby wolfcub1945 » Wed Sep 02, 2020 4:36 pm

I very much need help concerning a problem with the ignition system in my plane when I do a coil check. The plane is a Zodiac CH601XL. It has a Jabiru 3300 engine.

The problem is as follows:

• The engine runs fairly smoothly when the ignition switch is set to both (B). At this setting neither of the ignition coils is grounded. Note that grounding of a coil renders it inoperative.
• The engine runs smoothly when the ignition switch is set to right (R). At this setting the left (L) ignition coil is grounded, rendering it inoperative
• The engine dies when the ignition switch is set to L. At this setting the R coil is grounded, rendering it inoperative.

In the text that follows I refer to the ignition system as having two major subsystems. First, there is the ignition coil. Second there is a distribution system consisting of (a) a distributor cap, (b) a rotor, (c) spark plug wires, and (d) spark plugs.

Here is what I and three A&Ps with combined experience of about 60 years have done thus far:

• To determine what part of the L ignition subsystem is producing the problem, we did the following:

o Connected the high tension (HT) lead from the R coil to the L distributor. Since the engine runs normally on the R ignition subsystem we know that the R coil and R distribution system are functioning normally. So, if the engine runs normally with the R coil connected to the L distribution system, the L distribution system has to be good. With this setup the engine ran normally.
o Connected the HT lead from the L coil to the R distributor. Since the engine runs normally on the R ignition subsystem we know that the R coil is functioning normally as is the R distribution system. With this setup the engine died, suggesting that the L coil is faulty.

• I then ordered a new ignition coil from Arion Aircraft and installed it. The gap between the coil and the magnets on the flywheel was set at .010”, i.e., the recommended setting in the engine manual. I also connected the HT leads to their appropriate distributors, i.e., the HT lead from the L coil to the L distributor and the HT lead from the R coil to the R distributor. I then started the engine.
o The engine ran fairly smoothly when the ignition switch was set to both (B). At this setting neither of the ignition coils was grounded.
o The engine ran very smoothly when the ignition switch was set to right (R). At this setting the left L ignition coil was grounded rendering it inoperative.
o The engine died when the ignition switch was set to L. At this setting the R coil was grounded rendering it inoperative.
o On observing this result each of the A&Ps concluded (independently) that the problem must be the L coil, even though it was new and tested good when the resistance levels of the coil’s primary and secondary windings were measured.

Another possibility is that the ignition switch or the wiring from the switch to the coil is faulty. So, I did the following.

• Disconnected the P leads that run from the ignition switch to the ignition coils. By doing so, I eliminated the possibility that the switch was grounding either of the coils.
• This did not solve the problem.

I would very much appreciate any help that you may provide to solve the problem of the engine dying when the ignition switch is set to L.

Thanks in advance for any suggestions that you may provide.
wolfcub1945
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Re: Ignition system problem. Need help!

Postby PKnight » Fri Sep 04, 2020 2:31 pm

Thank you for a very clear explanation of the problem. Very helpful to understand even if I have no idea what is happening!

One comment:- I don't see why the engine would run less well, even if only slightly when both mags are connected. That should be the time of smoothest running. Perhaps there is clue in this behaviour?

One question:- Did this behaviour happen suddenly? If it did was there any change that preceded the event?
Another question:- When you switch to the left mag is the stoppage instantaneous or does the engine cough and stutter for a bit before stopping?

Whatever the result I hope you let us know what you find.
Sorry I cannot be more help at the moment.

Peter
G-PHYZ J430 Gen 4 engine
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Re: Ignition system problem. Need help!

Postby PKnight » Fri Sep 04, 2020 6:31 pm

There is one possibility that has to be eliminated.

Profound apologies if you have already considered and eliminated this.

In the switch the grounding wires have become reversed. So that when you think you have grounded the Left Mag you have actually grounded the Right Mag.
If this was the case you would have physically replaced the "good" left mag with a new "good" left mag. You then got the same result as the duff mag was actually the Right one which was undisturbed in this test.

Only absolutely certain way of checking is to make two new earth wires, one for each mag, and run them independently to the cockpit so you can safely earth each mag in tern with the engine running.

This would explain the result that you are getting. The only weakness is that I don't understand why the engine runs less smoothly on Both rather than on a single mag.

Peter
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