The Missing Miss

Where to begin?

Today started at Bob Carter's day job at Wildlife Materials. I had purchased a bag of diodes from our local Radio Shack and Bob said he could install them in the EC3. I figured I would drop off the unit and he would install them in a day or two. I was happy to see Bob put them in them right off the bat and I was out of there in 15 minutes!

You know on Sesame Street where they play "One Of These Things Is Not Like The Other"? Let's see if you can spot the two diodes. You can click on the photos to make them larger. Here is the before photo of the EC3.

And here is the after:

I'll give you a hint. R69 & R72.

The idea behind the switching diode is to condition the signal so it can be better read by the ECU. This is a fix if the signal coming from the sensors isn't behaving. Mine was certainly not behaving. In fact, it was downright rude.

For some reason, which I don't understand, as the RPMs increase, the amplitude of the waveform varies all over the place and that confuses the EC3. We have tried everything we could think of to flatten it out, but no luck. That includes stiffening up the brackets, fooling with the gaps, etc. ad nauseam.

For one final test today, I completely disconnected the backup sensor from all the ship's wiring, just to see how it looked on it's own. Here is the result. Notice how well behaved the wave is in the idle ranges, but it seems to go crazy as the engine speeds up.

While we were fooling around, I stuck another AN3 bolt joining the trigger bracket and the angle iron brace, attempting again to reduce vibration.

Perfect conditions for a flight test. Today is was 98 F in the hangar and the official temp on the ramp was 94 F. Even though it was a long taxi in the heat, I took no chances with the mods to the ECU and used our 5,500' runway. By the time I got to the departure end, the oil was already up to 135 F.

Takeoff is always strong, since the trouble doesn't happen at lower RPMs. Takeoff normal and I shallowed the climb to 800 FPM to keep the cylinder temps down. Because of clouds I only climbed to about 4,000', but the OAT was still 79 F and my density altitude was about 6,500'.

Leveled out, put the pedal to the metal and here we go. The RPMs climbed to about 2,800 and I turned off the mag, electronic ignition only. The engine remained smooth.

Went faster and tried it again. The engine remained smooth. Holy s**t, this might work.

Went faster yet and saw the tach bounce off 3,100 RPM. Haven't see the engine go that fast in a month of Sundays. Switched off the mag. The engine was still smooth!

Talk about elated... I kept flipping the ignition selection switch, trying to get a failure and there was none. We finally got it beat! Unbelievable!

Well actually, the root cause is still there, the misbehaving waveform. Tracy Crook's mod is a fix for a deeper problem and I still want to fix it, but at least I know I can race.

I let Sandy know right away and my second call was to Craig Catto who informed me that he was going to start making my new prop today! Certainly icing on the cake.

And best yet, when I got home, my grandaughter made fish tacos for dinner.