Secondary Ignition Troubleshooting

[Onex77]

Last Saturday while getting ready to fly down to the Florida Sonex Flyin my secondary ignition failed during my run up ignition check.(500RPM drop) Needless to say I was disappointed but taxied back to hanger to troubleshoot the problem. I pulled the bottom plugs all looked great except #2 bottom, little carbon not much so I installed new plug and give it a try. Run up was great problem solved. Cowled Onex back up and taxied out. Did another run up and secondary failed again :? So I taxied back to hanger again. Replaced #2 plug wire just for the heck of it. Still no good. Started reading how to check the coils out (3ohm across the screw term) and check coil towers ohm reading 15k ohm, both seem good. This only leaves the trigger modules. Next I pulled all the bottom plugs and grounded them to see if the plugs would spark while pulling prop though by hand with 12v to the coils, no joy. So I connected my meter from (grd - org wire on coil) to see if I could see a change as the magnet passed the trigger modules. The #1&3 trigger voltage pulsed every time the magnet passed the trigger module. The # 2&4 trigger module didn't, the meter would only drop about 1 volt to 11volts. So looks like the trigger module is the problem. On Monday I order a new trigger module and replaced this past Friday, Aerovee running like a top :D Sorry for the long story just hope this might help someone down the road if they have to troubleshoot the secondary ignition system.

[MichaelFarley56]

Great story Brent and thanks for sharing. I had a similar issue recently in terms of "symptoms" and when I checked one of my secondary ignition coils from main tower to tower, I got 0 ohms. Screw to screw ohms were fine but I still had a bad coil. A quick replacement and I also was back in business!

This is good stuff to know for people that may have a similar situation. Thanks again for sharing!

[rencurry]

Brent,

We have finally tracked our secondary ignition problem down to the trigger as well. We have replaced the left coil first and now the lower trigger trying to solve the problem. However, there was still no improvement.

The confirming test today was when we checked the voltage on the trigger wire on both triggers. The lower trigger we replaced showed no voltage drop as we pulled the prop through, but the upper trigger had the proper voltage drop.

We checked the ground path and the 12 volt supply, both OK. The only thing we are not sure of is how far the trigger should be from the rotor. Not surprisingly, there is no Sonex spec that we could find (and we called them) on how far to place the trigger from the rotor.

Right now, we have the trigger installed 0.020" from the rotor, but it still isn't working. We noticed that the old trigger and the upper trigger that is working, are scored from being right up against the rotor.

How far is your new trigger from the rotor?

[RodgerC]

I had an upper trigger die after a total life of around 1.5hours...I suspect they are a bit of a "consumable" item, so I bought a spare with the replacement to save myself the postage to Australia, the next time one gives up.

[Onex77]

I don't believe the trigger gap is important. The main thing is that the rotor doesn't hit the trigger unit. You could have another bad trigger unit. Not sure how old your engine is, Make sure you have the new rotor with larger magnet. The rotor magnet triggers the module and sends 12v pulse to fire the coil. I can measure my trigger gap and get back with you but 0.020 sounds right.

[rencurry]

Brent

Thanks for your comment. I just read your post, so I haven't been to the airplane to check on the rotor, but the rotor must be OK since everything was working fine before and we get a voltage drop with the upper trigger.

If your trigger gaps are 0.020 inches, then our trigger must be bad. We'll move it closer to the rotor, since that is the only remaining thing we can do, but I would like to know what your gaps are for future reference. You will be the missing Sonex spec!!

--Ren

[kmwoody]

Ren

Don't be so sure the magnet is not bad. Long story short, I went through two new triggers, a new coil and hours of troubleshooting and testing before I finally ordered a new magnet. I didn't order a magnet (rotor) because "everything was working fine before". When testing the new magnet against the old magnet, against a refridgerator, the old one fell from the fridge and the new one had to be pulled off the fridge.

Also I thoroughly enjoy replacing all the expensive parts first and the cheapest last.

Ken W

[rencurry]

Ken,

Thanks for your comment. It sounds like we are following the same expensive path.

One wrinkle for us is contact with the rotor/magnet. Here is part of an email from my partner

"So we are at this point ..as the Rotor/Magnet rotates it pushes the trigger away leaving a large gap. The little screws that hold the trigger in place are just too small to take the side push from the Rotor/Magnet. There is a design flaw or bad build in the system. Perhaps, the prior owners ground down the the upper and lower triggers before installation ? to make the flawed design work, albeit temporarily until it breaks again."

Has anyone else run into this?

--Ren

[Loiret39]

hello all,
I have the same problem with my secondary ignition, and i want to change the magnet, but i didn't find is reference on the aerovee catalog!
Do you have this reference?
Regards
André

[SNX1508]

From Sonex tech support in July 2016..... "A new magnet cap is part number ACV-F01-21".

Terry L. Cooper
SNX #1508 Tail Wheel
AeroVee #0736
N296SX
Aircraft build = 2005 hours, and was completed in October 2016
http://www.mykitlog.com/SNX1508
FAA Inspected & Airworthiness Certificate issued 11/4/2016
Currently training in a Citabria for tail wheel experience, then onto a LSA for ASEL endorsement on my Sport Pilot cert.