gitmo234 Posted August 11, 2017 Report Share Posted August 11, 2017 Landing thread aside, I’ve got a new issue. Rough mag check, dramatic drop, followed by a backfire on my left mag. I lean it out, play with it for >5 but <10 minutes and it will check fine. Check again is hit or miss, lean again and it will check fine, at the same time my fuel flow analyzer sometimes takes a tap or two on the screen to come on. May or may not be related. im hoping it’s a bad plug and that’s it. I lean on the ground. Any thoughts? It does the same on a pre shutdown mag check Quote Link to comment Share on other sites More sharing options...
neilpilot Posted August 11, 2017 Report Share Posted August 11, 2017 Have you tried an in flight mag check? Quote Link to comment Share on other sites More sharing options...
jasona900 Posted August 11, 2017 Report Share Posted August 11, 2017 21 minutes ago, gitmo234 said: Landing thread aside, I’ve got a new issue. Rough mag check, dramatic drop, followed by a backfire on my left mag. I lean it out, play with it for >5 but <10 minutes and it will check fine. Check again is hit or miss, lean again and it will check fine, at the same time my fuel flow analyzer sometimes takes a tap or two on the screen to come on. May or may not be related. im hoping it’s a bad plug and that’s it. I lean on the ground. Any thoughts? It does the same on a pre shutdown mag check Any hints from the engine monitor? I had something similar very recently, and turned out to be a bad #3 plug (the lower one as expected). The engine monitor showed a low EGT on that cylinder when I did my run-up. Looking at the plug I pulled, there was a big glob of lead at the bottom of the plug. My plugs were old, and almost all of them failed the ohm test. I put 8 fine wires in, and it's been running smooth ever since. Quote Link to comment Share on other sites More sharing options...
Yetti Posted August 11, 2017 Report Share Posted August 11, 2017 Plugs - how many hours on Mag showing bad? Did you try clearing fouled plugs. Run high RPM and lean? Quote Link to comment Share on other sites More sharing options...
Yetti Posted August 11, 2017 Report Share Posted August 11, 2017 Do you lean aggressively on the ground? Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 11, 2017 Report Share Posted August 11, 2017 1) +1 on mag hours... 2) What plugs are in there? Champions? Got a tool to measure resistance? 3) leaning while on the ground... 4) +1 for engine monitor... what is it indicating? Got a screen shot? 5) Sounds like a plug isn't firing properly... PP thoughts only, but, I really like team problem solving.... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
gitmo234 Posted August 13, 2017 Author Report Share Posted August 13, 2017 Not meaning to go quiet on this. My schedule is just pretty crazy. I've gotten a few PMs from others too with what their problem is and how they handle it. My local shop recommended a ground test of full takeoff power for about 5 seconds or so and then re-try. If the mag check fails again its likely a mag problem. if it doesnt fail then its likely a plug. I'm going to dig in my logbooks for mag hours. I'm familiar enough with my engine monitor to speak about it but will snap a picture next time I'm running it up. #2 always seems to be a bit lower though. Quote Link to comment Share on other sites More sharing options...
Marauder Posted August 13, 2017 Report Share Posted August 13, 2017 Not meaning to go quiet on this. My schedule is just pretty crazy. I've gotten a few PMs from others too with what their problem is and how they handle it. My local shop recommended a ground test of full takeoff power for about 5 seconds or so and then re-try. If the mag check fails again its likely a mag problem. if it doesnt fail then its likely a plug. I'm going to dig in my logbooks for mag hours. I'm familiar enough with my engine monitor to speak about it but will snap a picture next time I'm running it up. #2 always seems to be a bit lower though. Is Roger working on it? If so, you're in good hands. Sent from my iPhone using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
gitmo234 Posted August 13, 2017 Author Report Share Posted August 13, 2017 Just now, Marauder said: Is Roger working on it? If so, you're in good hands. Sent from my iPhone using Tapatalk Pro He's going to take a look. He made the recommendation on trying the full power for a bit and then re-checking. he took care of my 172 as well 1 Quote Link to comment Share on other sites More sharing options...
gitmo234 Posted August 15, 2017 Author Report Share Posted August 15, 2017 Roger found it. I had an issue on/in my left magneto. It was a phone call during my commute so my terminology may be a bit fuzzy but it was something like "distributor block" on the left magneto was toast and the bushings were loose (likely cause of the block being bad or something). Should be all put back together tomorrow 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 16, 2017 Report Share Posted August 16, 2017 When doing mag service, know the goofy problems that surface... like re-used lock washers... don't work like new lock-washers... That can cause a certain looseness of the newly OH'd mag... PP thoughts only, an event that shows up every now and then... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
jetdriven Posted August 16, 2017 Report Share Posted August 16, 2017 Slick mags will melt the distributor rotor and it falls apart. Bendix mags can melt the distributor block bushing if it wasn't baked with oil in it at the 500hr inspection per the service manual. What kind of mags do you have. Quote Link to comment Share on other sites More sharing options...
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