After months of fighting it looks like we got the problem fixed. Just like most similar problems, this one is actually quite simple and explains other issues I thought were unrelated.
After changing the ignition switch to eliminate the possibility of an internal ignition P lead short I went on a test flight. Doubting this was the problem, I decided that if the problem continued I would do several other in flight tests. I coordinated with the tower to stay over the approach end of the runway during the flight.
With all the ground tests completed and passed, I took off and climbed without issue to 1,500ft just as the tower had cleared me. A few minutes after reaching 1,500ft the engine started to run rough again. Knowing I was within easy gliding distance of the runway I got up the guts to do the “in-flight” single magneto check. I switched to left mag only and, as I expected, there was absolutely no change in the engine performance. It continued to run a bit rough. When I switched to right mag only, complete and absolute silence. THE ENGINE HAD QUIT!
With “pucker factor” at a maximum, I switched to both magnetos and the engine came back to life but still running a bit rough. With this new information I decided to land and as I descended, the engine started running smooth as silk again. Once on the ground I tried everything I could to reproduce the problem with no avail. The engine continued to run smooth. But now I know without a doubt I had a magneto problem.
I called Brad (E-Mags) who has been working with me on this problem from day one, and told him what happened on this flight. With this information he speculated both magnetos have separate problems, one problem masking the other. My left magneto has a problem causing it to run slightly rough. The right magneto compensates when it is working correctly and covers the problem. When the right magneto cuts off for that brief time frame, then the left magneto’s problem manifests itself until the right magneto comes back on line and the engine runs smooth again. I downloaded the data from my EMS and we could see it happening in perfect harmony with the symptoms. Brad told me to ship him both magnetos (making sure I identified which was which) and he would abuse them in his shop to figure out if this is what is actually happening.
In addition to explaining why the engine ran a bit rough only once in a while it explained two other situations which, until then, I thought were completely unrelated to the intermittent stumbling issue. 20/20 hindsight.
About a week after installing the magnetos (Oct 2013) I was going to take a short local flight when, while doing the engine run up, the RPM indications on my DYNON SkyView EMS dropped to zero even though the engine continued to run smoothly. No matter what I did the RPMs stayed at zero with the engine still running. I aborted the flight and checked the wiring. Finding nothing wrong I called DYNON and we realized I had configured the computer to read only from the right magneto. Since I had not installed the 33K resistor on the magneto tach sensor line we figured the computer had disconnected the signal which explained why I had no RPM indication even though the engine was still running smooth. We configured the computer to read from both magneto’s and have not had the problem since. With 20/20 hindsight this might have been when the right magneto computer board started having its intermittent problem but the left magneto, which was operating fine back then, compensated and covered the problem. BTW: With the Skyview EMS you do not install a 33K resistor with the E-Mags only the 5.1v diode on the tach line.
Then, back in January 2014, I was doing an engine run up prior to a flight when I felt the engine running different. I couldn’t pinpoint why, but it just felt different to me. But no matter what I did during the run up everything looked fine so I continued and had an uneventful flight. A few flights after this the intermittent roughness during cruise flight started. I am speculating that this is when the left magneto started acting up and I have been chasing two ghosts ever since. Again, hindsight is 20/20.
Brad received the mags but didn’t find any “smoking gun” when he tested them. However, since the right mag had stopped sending a tach signal before and had stopped operating in flight he decided to change the PC board in it. He also sent me a new wire harness for the left mag and told me to replace the spark plugs with new ones. The only thing Brad charged me for all of this work was shipping the mags back to me.
We installed the magnetos, the new wiring harness and replaced all the spark plugs on Saturday. I did multiple ground tests and everything passed with flying colors. By the time we had everything closed back up it was night so I decided to do the flight test on Monday.
For testing I made the flight with the left magneto on ship power but the right magneto on internal power only. This insured that if there were something wrong with my electrical system at least one magneto would not be affected. I climbed to 1,700ft and stayed over the approach end of the runway for 45 minutes. Everything went perfectly smooth. Not one hiccup, stumble or any other abnormality. I was one very happy camper when I landed.
Being the belt and suspenders kind of guy, I am still a bit apprehensive that the problem is fixed but it really looks like we got it. The next few flights will just be just hops around the pattern until I have flown about 5hrs without a stumble of any kind. Only then will I start going further away as I get more confident this has completely eliminated the problem.
I want to thank everyone here that has helped during these baffling times especially Bill (N941WR), Kahuna and Brad at E-Mags. Brad and I talked multiple times during the ordeal and he never tried to push the blame somewhere else just kept a logical troubleshooting sequence until he nailed the problem. His customer support is superb and I am glad I went with his magnetos.
RPM Surges
Linear Mode
