Well, we were going to fly to Utah this weekend, but didn’t. The plan was to leave late Friday afternoon for a two hour flight to St George and then fly to Salt Lake on Saturday. The weather forecast earlier in the week was questionable so everything was ‘tentative.’ Flight plans were filed and a briefing was done online Friday morning that looked promising so I packed a bag and took it to work with me.
By late afternoon we were at the hangar, pre-flight was completed, and we loaded up the plane. After parking the cars in the hangar and locking it up we climbed in, started up, and taxied out to the run-up area. I set the throttle at 1,700 rpm’s, set the engine monitor to normalize mode to watch the EGT’s (Exhaust Gas Temperatures) more closely, and started the mag check. Switching to the right mag, it looked good. I switched to the left and the #2 cylinder was dead, not just weak, but dead. I switched back to both mags and we taxied back to the hangar…
One of the many great things about having the engine monitor is that it shows you exactly which cylinder is the problem, and which plug. I pulled the cowling cheek off to take a look at the offending plug and found that the plug wire was loose. I grabbed a couple wrenches, snugged the wire back down, put the cowling cheek back on and we started up and taxied back to the run-up area. My son asked “What if it doesn’t work?” I was confident I had found the problem and told him “It will.”
Same procedure, right mag was good, left mag… dead #2 cylinder… Rats… Oh well, back to the hangar we go. This time I pulled the plug to take a look. I would have pulled it the first time but thought the loose wire was the culprit. I had just flown three days prior on a return to service flight after having the prop re-sealed and it had run fine then. When I pulled the plug I found that there was buildup on one of the ground electrodes that connected to the center electrode and had the plug shorted out. Well, we weren’t flying to Utah that day…
I hopped in the car and fought my way through Friday SoCal traffic to arrive at Aircraft Spruce 7 minutes before they closed to pick up a new plug. I also bought a spare to keep in my tool box, just in case. Thankfully this happened while I was at my home airport and not on the road. At least in the future if it happens I will have the tools with me and a spare plug to change it on the road.
I decided that while I was replacing that plug I would pull the other seven to clean and gap them, just in case there was some buildup on any others. Saturday morning I pulled all the plugs, and none of them had any buildup on the electrodes but all had too large a gap and needed to be adjusted.
Before cleaning 
After cleaning
With all the plugs cleaned, gapped properly, rotated to new cylinders, and reinstalled it was time to taxi to the run-up area and ‘hopefully’ go for a short flight. Throttle set to 1,700, engine monitor set to normalize, right mag check, left mag check, everything looked great. After finishing the run-up I talked to ground and was cleared to taxi to runway 24 via Alpha.
It was just a short flight East over Yorba Linda and the engine ran great, nice and smooth! It was a little bumpy but the sky was beautiful and it was nice to be flying.
As I turned off the runway the tower called me up.
Tower: “Mooney 878, state taxi intentions, and just to let you know at about 1 mile final your transponder dropped out.”
Me: “Request taxi back to the south-east hangars.”
Tower: ” Taxi via Alpha.”
Me: “Taxi via Alpha, and was it just the Mode C that dropped or the whole transponder?”
Tower: “I lost everything, I didn’t even have your primary.”
Me: “Thanks, 878.”
One thing fixed, and another to be looked at…