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Old 11-08-2021, 02:41 AM
Gahunter Gahunter is offline
Join Date: Sep 2009
Location: Lake Jackson, TX
Posts: 3
Smile Rotax 912ULS Ignition Noise

I recently bought this brand new (<30 hours) RV-12 with the 912-ULS. It has this rather weird ignition noise with incoming transmissions only. Whenever the aircraft is pointed at or flying towards a transmission source, air to air, ground to air (ASOS for instance), there is a rather loud ignition noise the sometimes drowns out the transmission. Turn the aircraft 180 degrees and the noise is gone. Transmissions received from 90 degrees seem to be OK too.

I have tested and ruled out headset issues (BOSE A20's, radio installation and coax wiring issues previously discussed. The ignition modules are properly secured, shielded and grounded. Switching between A & B ignition makes a very very slight difference when B is off. This indicates, it is ignition related. It varies with engine speed, and the directionality of this problem also indicates it has to do with the engine when it gets between the source and the antenna behind the pilot seat on the belly per plans. An alternator issue usually produces a whine rather than this static type ignition noise reminiscent of the noise we would get with aftermarket stereos in automobiles from 60's with spark plugs without resistors.

SO - Has anyone else experienced this ? Has anyone ever experienced a bad set of spark plugs or wires ?
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Old 11-08-2021, 07:29 AM
bobg56 bobg56 is offline
Join Date: Nov 2018
Location: Peachtree City, GA
Posts: 204

The wires coming from the shut off switches are shielded wires and are grounded to a clamp on the ignition module clamp, as I understand it thats the only place, (not at the switches as well), I'd make sure thats intact.
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Old 11-08-2021, 10:24 AM
Gahunter Gahunter is offline
Join Date: Sep 2009
Location: Lake Jackson, TX
Posts: 3
Thumbs up

Thanks for that input. Iíll look into today.
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Old 11-10-2021, 03:41 AM
Gahunter Gahunter is offline
Join Date: Sep 2009
Location: Lake Jackson, TX
Posts: 3

Problem solved. I pulled all the spark plugs and found that the two lower front (cylinders 1&2) plugs had been damaged from what appears to be some sort of handling or shipping issue. The terminal on top of the spark plugs were bent approximately 30 degrees. For that to occur, there had to have be sufficient force to cause other non-visible issues with the plug. Mind you, this happened with the rubber plug wire cap in place. Plus, the plug wire cap on #1 bottom had been knocked loose from the internal terminal connector such that the rubber boot and tie-wrap was the only thing holding it in place. No more ignition noise.
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