912 installation, RV12; engine new/stocked 3 yrs. before delivery. TTSNEW less than 5 hrs. Symptoms: Top3/4 no spark. This has NEVER run right; mag drop originally 100/1300; resolved now to 900/125. We are confirming NO SPARK at top 3/4 with induction timing light; TOTALLY NO SPARK. 'New' style modules/ trigger connectors/ ignition coils  ...tests:

A. Checked installation wiring, corrected inadequate ground at ignition module [ poorly installed pin connector - supplied by Van's].

B. Balanced carbs.Checked choke circuit. Checked carb installation. Checked wiring installation to A/C. Checked spark plug gap, temp paste, plug wire ends/ install.        This brought us to 900/125.  Owner then followed remote instructions, doing various checks -- called me back in.

C. Checked condition/ gap for trigger coils; regapped A 3/4 [set at less than 0.0010 from factory]. Cleaned and polished all. No change.

D. Swapped module B for A. No change. [repeated prior check so I could observe/ check it off]

E. Checked trigger coils: 'A' cold 239.1/ 239.2; 'B' Cold 240/240.3; 'B' after running [to low op temp, then to 'warm to touch' temp] 249.4/250.6 ohms.

F. Swapped 'B' for 'A' triggers. No change [repeated prior check so I could observe/ check it off]

G. Swapped 'B' for 'A' module [at the plugs]. No change. [repeated prior check so I could observe/ check it off]

H. Checked stator coils: 4.4 ohms, both 'A' and 'B'.

I. Given symptoms, strongly suspect failed coil. Attempting to check resistance of ignition coil for Top3/4, i get discontinuity; however, similar check on Bottom3/4 shows the same.

--- Which leads me to: A&P, been wrenching lots of years, but last took the Rotax course in 2014. Not sure I'm testing the coil properly, and can't get a reading for the plug wire/ connector, either. HOW DO I HOOK MY METER TO GET A READING ON THESE COMPONENTS????? Yes, please, draw me a picture, i'm apparently that dumb. And, no, there is nobody more experienced within 100 miles of here. shouldn't be this hard to diagnose.

If this was a Lyc, I'd have had the d#### thing flying many hrs ago. Was thinking about buying a motorglider, now not so much if it has one of these.

FOCUSED help would be greatly appreciated; owner has been fighting this for months, trying to get new A/C ready for Phase 1 flight test.


  • Re: ignition failure

    by » 3 years ago

    The Rotax 912 Heavy Maintenance manual has a diagram that shows the various connections in the ignition system. You should definitely be able to measure the resistance of the primary and secondary windings in the coils. I have attached the diagram below.

    I usually measure the secondaries by just pulling the plug caps off the plugs and measuring from inside the plug cap to the other plug cap that is connected to that coil. e.g. 1T to 2T, 1B to 2B, 3T to 4T and 3B to 4B (T=top, B=bottom). You will be measuring the resistance of the plug caps as well the secondary winding. This will tell you whether the coil is open circuit or not. The plug caps are about 5k ohms each and the secondary coil is about 6.5k ohms to the total should be approximately 16.5k. This doesn't tell you whether you have a shorted turn or an intermittent connection.

    The primary windings can be measured between the white & blue pairs in the 6 way connector. The attached diagram has the connector pin out. The resistance is very low so you should definitely be able to measure it. Again this doesn't tell you whether you have a shorted turn or an intermittent connection.

    Unfortunately it is not easy to swap over the coils, if you have a spare pair of 912 coils then you could substitute them but I'm guessing that is not an option. If you have a suitable crimp release tool then you could swap the primary connections to the 3T/4T with the 1B/2B connections. You can leave the plugs out and connected and just see if you have a spark when cranking. If the problem has now moved to the 1B/2B plugs then the coil is your problem.

    Here's a link to the manual https://www.rotax-owner.com/manuals/MMH_912-914_Series_ED1_R6.pdf

    30913_2_912 Ignition.png (You do not have access to download this file.)

  • Re: ignition failure

    by » 2 years ago

    Thank you, sir.

    A. I have the manuals - all FIVE for the 912/914. Have kept them current since 2014. Wouldn't turn a wrench on anything if i didn't. [Need an OH manual for a P&W R-985? Parts manual? How about a Wright 1820?] My usual for these runs more to the hose replacement, carb float check/carb ops check,  carb balance, or pulling the gearbox to send it out.

    B. I appreciate the insight into testing across the two plug wires. Hopefully I can get SOME value to show up.

    C. I tested across the pin as described - FAIL [discontinuity] ---- which is why i was suspecting a bad coil.  I will re-test, see if I can confirm, then chase for failed connections before we order parts.

    And, you are correct - I don't see these often enough to stock parts. Hate to tell owner he needs to buy parts - which will have been defective from factory - on the guess that pull-and-plug will fix it.... especially with those modules at $900+ each. Need to keep people safe, but handing an owner a big bill doesn't help accomplish that.

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