Help! Ignition Gremlin?

by Av8r3400 . in 912 / 914 Technical Questions 8 years ago

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Re: Help! Ignition Gremlin?

by Av8r3400 . » 8 years ago

Av8r3400 .

2 23 0

Lockwood checked the ignition modules. They are both good. This is a good news bad news situation in that it isn't going to cost me $1200 for a new module but now I am back to square one for trouble shooting the problem.

I should have the modules back in a couple of days and we start all over again.

For the record I was in error on the wiring diagram, the correct one for my engine is 74-18. (74-21 is for the the 914)

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Re: Help! Ignition Gremlin?

by Roger Lee » 8 years ago

Roger Lee

126 5.13k 4.56k

"Problem:
When doing ignition check one module has ~50 rpm drop and other has 400-600 rpm drop with skyrocketing EGT on #3 & 4 (only ones monitored, will quickly pass 1600F"

This may not be an electrical problem at all. You could have a fuel and or air leak issue. The ignition modules would not have caused the extreme EGT swing. That is caused by an air leak or something causing a very lean condition. An extreme lean condition would cause the rpm issue. If it were electrical with that big rpm drop that means plugs aren't firing and fuel isn't burning. No fuel burning means cooler EGT's not hotter ones.

Target your efforts at making sure each carb opens fully, that the diaphragms in the carbs are in there correctly, use the carb sync gauges and advance the throttle as far as you can and watch to see if the needles split, really look hard for an air leak. Air leaks cause hot EGT's and rpm loss. After a long down time your carbs may need to be stripped and cleaned or even overhauled.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Av8r3400 .

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Re: Help! Ignition Gremlin?

by Av8r3400 . » 8 years ago

Av8r3400 .

2 23 0

An ignition module misfiring one side 180º out, in effect firing it with the other side, which is possible according to Lockwood, will cause the fuel air mix to burn when the exhaust valve is open. This would spike the EGT, causing a large rpm drop but not stopping the engine. This was the theory I was working on when I sent the modules down to them for testing. The modules have since tested fine. So that theory is out the window for now.

As I noted in the first post the carbs were removed, disassembled, cleaned, inspected (weighed floats, replaced some o-rings, etc.), reinstalled and synchronized. The sockets and the intake o-rings are new.

Help me understand how a lean condition will only exist when one ignition module is turned off. That makes no sense to me. You must have a theory of some sort on this.

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Re: Help! Ignition Gremlin?

by Av8r3400 . » 8 years ago

Av8r3400 .

2 23 0

After a weeks worth of exhaustive elimination testing the problem has been localized to the CDI boxes.

I had them tested at Lockwood, but their testing does not test for proper function, only function.

I cannibalized two boxes from another, properly running, airplane and with both of them installed the engine runes fine. 120 rpm drop both sides, better starting and smooth running. With one good and one bad, the problem is manifest. Either bad box, installed in either position will cause the problem described at the beginning of the thread.

I believe there is a ground fault in both boxes because that is the only common link between the two ignitions.

Now I have to pay the ridiculous, unserious rates of nearly $2500 for two boxes to run this engine. I am thoroughly disgusted with both Lockwood for wasting my time and money doing a worthless test and Rotax for charging $1227 apiece for a $50 Ducati ignition box.

Report
Re: Help! Ignition Gremlin?

by Av8r3400 . » 8 years ago

Av8r3400 .

2 23 0

After a weeks worth of exhaustive elimination testing the problem has been localized to the CDI boxes.

I had them tested at Lockwood, but their testing does not test for proper function, only function.

I cannibalized two boxes from another, properly running, airplane and with both of them installed the engine runes fine. 120 rpm drop both sides, better starting and smooth running. With one good and one bad, the problem is manifest. Either bad box, installed in either position will cause the problem described at the beginning of the thread.

I believe there is a ground fault in both boxes because that is the only common link between the two ignitions.

Now I have to pay the ridiculous, unserious rates of nearly $2500 for two boxes to run this engine. I am thoroughly disgusted with both Lockwood for wasting my time and money doing a worthless test and Rotax for charging $1227 apiece for a $50 Ducati ignition box.

Report

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