AZOutlaw

Yes it was Bruce and I agree, he's great! I took the left mag to him yesterday and he tested it out. It appears we got a bad capacitor. He put it on a tester and we could see intermittent sparks. Not a lot but you could sure see a few drop out. He found an old capacitor in a drawer and put that on and it cleared things up. He didn't have a new part to match so I'll get it back next week and update the results.

Thanks guys, just a refresher. It's a brand new harness two weeks ago and it was tested, for good measure, last week. Mags were rebuilt this summer and only have 6 hours on them. I'm very familiar with burning off fouling and have done that numerous times. Timing has been checked and re-checked. Fuel injectors were removed and cleaned. I'm leaning towards the fact that my Magneto rebuild didn't get rebuilt properly. We pulled them out and sent them in when this started after first replacing the spark plugs. The problem was there before the rebuild and remains still.

Update: Bottom line, the problem still exists. We checked the timing and did think it was off a little so we adjusted that. Fired it up and first check had the same result. (-150 Left and -40 Right) We shut it down, discussed a few things and decided to try again. This time it was perfect, about a -35 mag drop on each side, or what it always did in the past. Took it up and all seemed good. In flight mag checks were equal and uneventful. Landed and did a check before shut down and got a -65 on the left. Went back a day later and got the same (-150 Left and -40 Right). Borrowed a different timing box, bumped them slightly and felt they were perfect, same result and this time the inflight test was bad on the left, like it was a week ago. Swapped bottom and top plugs thinking the issue might move to the other mag. It did not. Same result, but what is interesting is I did the second start up 30 seconds after shutting down as before, and got perfect mag drops again. This got me thinking heat and resistance was an issue. Pulled all the plugs and did a resistance test, twice, and got these readings. Seems that 5B is reading low and 3B is high but all the rest are really close. I found this online. "Champion Spark Plug Company’s Engineering Manual gives the nominal value for their resistor type of aviation spark plugs as 1000 - 1500 ohms" Anyone have real world experience on what is good and bad readings for a Champion plug?

Thank you and that's where we are headed. Just wondering if there is a better way to time a Mooney than with an antiquated sundial attached to the spinner? Surely technology has caught up to that too.

Here's some info I got today. The Left mag side is definitely hotter. I did the inflight mag check as well. At first I ran it out to LOP and it was in the high 1400's. When I did the Left check, everything immediately went off the scale. The ships single EGT gauge went way past redline so I quickly backed out of that. I went richer with the mixture and got a lower base EGT and ran the same check. The right side was smooth and normal. All EGTS rose some but nothing drastic and the engine was still smooth. The Left EGTs took off in different directions and the engine got rough. I had video and at the bottom is a screen shot just before the mag check, the second screen shot is 4 seconds after turning the key.

Everything leads to timing I guess. It started in JAN and we changed the plugs. We then sent the MAGS out for rebuild and after a lot of delays got them back and installed with the same result. After that is was the injector clean out and then yesterday, a new wiring harness. Waiting for the rain to clear out and then I plan to test it more today while watching EGT's closer.

Probably 8 hours on the plugs. 25 minutes on the wires and the clean injectors. 6 hours on the rebuilt mags. Plugs are Champion RHB32E, massive and yes, we checked resistance. I honestly can't remember if he checked them all though.

I have these and they both tell me the same thing.

Thank you Marc, I have a JPI EDM 800 but I can look at the EGT's closer tomorrow. I thought I would put bottom plugs on top too, and tops to bottom, and see if the problem switched to the R mag.....then it's a bad plug.

Thanks Hank, but I have brand new wiring as of today. I think they're good.

It started before the mags were serviced.

We've been chasing an uneven mag drop for a few months now on an Ovation with IO 550 G. On the run up, the Left mag will drop and 120 to 145 and Right seems to always be between 40 and 50. They both used to be in the 40 to 50 range, for years. We have replaced the spark plugs, rebuilt the magnetos, cleaned the injectors and replaced the ignition leads. We also did the annual during this and all compressions were good. Any thoughts on what to look at next? Ignition switch is best guess.

Problem solved. I was trading emails with Jason at CAV ice and after disconnecting the TKS lines to the switch, we still had a high pressure light. Jason said we could send it in for a rebuild so we went to figure out where to cut or disconnect the wiring. I was a little confusing as the wire diagram shows 2 wires, the switch has three. I'm going to assume the NO wire just dead ends in there somewhere. Long story but we pulled on one of the wires and it came right out. Pretty sure it was chewed up as I probably got a hitchhiking mouse sometime during my travels this summer. I bet that was one hell of a ride!! I connected the two ends and the light is off. Now just need to go back and solder together. Thanks for all the help and comments. A big thanks to CAV. They really are an exceptional resource!! Happy Flying, Sonny

It's been around awhile but I only buy the 2.5 Gal bottles so I don't have a big drum of it. I live in AZ and we rarely see ice!! I dumped in a new bottle the other day and ran a good portion of that out on the ground thinking that might be the case. The stuff in the tank has been in there a couple of years but it was down to about 3 gallons. I'll admit, I don't run it monthly as CAV suggests as I hate the clean up and the dripping in the hangar for the next 2 weeks. Anyone know what "Minimum Dispatch" refers to?

I have a continuous High Pressure light on the TKS panel. CAV Ice's recommendation is to change the filter, which we did, with the same result. I have tried the reset button and it does shut the light off occasionally, but not always. If it does go off, it comes back on soon. I've run a couple of gallons of fluid through the system recently as well. Any thoughts on what to check next? I'm guessing it's a bad pressure switch, but while I do have wiring diagrams for what seems to be all Ovations, I can't find anything that has the TKS wiring included.