Sport Pilot Talk

roger lee

Hi All,

Thinking ahead.

I'll give this scenario and see if someone can tell me what the problem is and where to look to solve it. I'll give it a day or two for answers then I'll give the answer to the problem. I was called with this problem the other day and it was solved in about 3 minutes.

You start your engine and go fly and everything seems normal. When you land and turn off the key the engine keeps running at a very slow rpm and it looks and sounds like it is running on one mag. What's wrong and where might you look to find the problem?

p.s.
Don't over think it and start at the most obvious potential solution.

Jim Stewart · Joined: 12 Oct 2006 Posts: 259

Broken P-lead or bad mag switch.

cerwindel · Joined: 01 May 2011 Posts: 13 Location: Tracy, Ca

Switch that controls the key broken? Perhaps stuck halfway even though the switch turns off?

Happened to me on a Cessna not that long ago, damn switch busted, key was useless..

C

roger lee · Posted: Mon May 09, 2011 10:08 am Post subject: Problem resolution

Here is the answer to this particular problem. It was a broken white ground wire going into one of the ignition module pin connectors. There is one white ground wire that goes into each plastic pin block and it is in a corner hole on the pin block. I always say something is finger tight, but wrench loose and the same goes for wiring. So unless you grab each wire and look at it from start to finish it may be broken or pinched or chafed against some metal or hanging by a thread causing a poor connection, ect...
Here is the clue that made me tell him where to look first. The plane ran fine at all rpms. Only when he turned the key off it did not want to shut down completely. He said it sounded like it was running on only one ignition module (mag) and of course at a reduced rpm. So it sounded as if one mag was shutting down, but the other was not. So the very first thought should be if one is shutting down why isn’t the other. When you turn the key off it should ground out. So for me the first thing to check before bouncing all over looking with no logical direction was to look at both ground wires since they are easily accessible and usually easy to visualize. While I was talking to this gentleman on the phone telling him which wires to look at he was grabbing one of the white wires and it came out of the plastic pin block at the ignition model broken. He said he just barely tugged it and it was out. This is the ignition ground wire. It was broken up inside the pin block where it was crimped. By replacing the crimp on the end of the wire he was ready in short order. Yes there could have been another problem somewhere else, but the idea here is to start in the most logical and easiest area to inspect first.
I guess the moral of the story is to develop good diagnostic skills and then teach yourself to start at point “A” then to “B” and so on. You need to know where the starting point is and where the most logical problem area is and start from there. Eliminate all the easy most logical points first then you can tear into more hard to reach or costly areas. This approach will save you time, money and aspirin for the headaches.

I hope this story helps someone that may have the same type of engine shut down issue with a starting point for your resolution.