Help with inflight mag check results

[Flying again!]

I have an RV-10 with an O-540 and 2 Slick Mags (6351 and 6350). I just had them reconditioned at AIS. During the first flight after reinstalled and timed I did an inflight mag check (23”/2300 rpm). The Left Mag was smooth with EGT rises in all cylinders. The Right Mag ran very rough to the point I went back to both, reduced power to ~18”/2150 rpm and switched back to right mag and saw cy 1 EGT was down over 200 deg.

Cylinder 1 Right Mag fires the bottom plug. I removed the plug and checked the gap, resistance and cleaned it. In the tester with pressure it fired fine. I installed this plug in the top and put the top plug in the bottom so if the problem moved to the Left Mag then it would show there was something wrong with the plug.

On the next flight the Right Mag Ran smoothly with EGT rise across the board as shown in the tables below. However, the Left mag now ran rough but not isolated to #1 cylinder, 3 cylinders had a drop in EGT and 3 had a rise.
The plugs are Tempest UREM40Es with ~100 hours on them and all cleaned and gapped at the condition inspection ~3 hours ago.



The timing was checked and it had not changed. I wanted to make sure the internal timing had not changed due to a failure with the impulse coupling etc.

Now what? I bought a new plug to replace the original suspect plug but doubt that would cause the rough running and affect the other cylinders. It is puzzling that the Left mag ran fine on its own the previous flight and the Right mag had a misfire on #1 cyl and after swapping top and bottom plugs, Right runs fine and left has issues with 3 of the cylinders.

Any Ideas??

Forgot to add that the mag check on the ground is good with about a 70 rpm drop at 1700 rpm with Left and Right mags. The issue is with inflight mag check.

Thanks – TJ

[lr172]

Originally Posted by Flying again!

I have an RV-10 with an O-540 and 2 Slick Mags (6351 and 6350). I just had them reconditioned at AIS. During the first flight after reinstalled and timed I did an inflight mag check (23”/2300 rpm). The Left Mag was smooth with EGT rises in all cylinders. The Right Mag ran very rough to the point I went back to both, reduced power to ~18”/2150 rpm and switched back to right mag and saw cy 1 EGT was down over 200 deg.

Cylinder 1 Right Mag fires the bottom plug. I removed the plug and checked the gap, resistance and cleaned it. In the tester with pressure it fired fine. I installed this plug in the top and put the top plug in the bottom so if the problem moved to the Left Mag then it would show there was something wrong with the plug.

On the next flight the Right Mag Ran smoothly with EGT rise across the board as shown in the tables below. However, the Left mag now ran rough but not isolated to #1 cylinder, 3 cylinders had a drop in EGT and 3 had a rise.
The plugs are Tempest UREM40Es with ~100 hours on them and all cleaned and gapped at the condition inspection ~3 hours ago.



The timing was checked and it had not changed. I wanted to make sure the internal timing had not changed due to a failure with the impulse coupling etc.

Now what? I bought a new plug to replace the original suspect plug but doubt that would cause the rough running and affect the other cylinders. It is puzzling that the Left mag ran fine on its own the previous flight and the Right mag had a misfire on #1 cyl and after swapping top and bottom plugs, Right runs fine and left has issues with 3 of the cylinders.

Any Ideas??

Forgot to add that the mag check on the ground is good with about a 70 rpm drop at 1700 rpm with Left and Right mags. The issue is with inflight mag check.

Thanks – TJ

Suggest more testing. Quite logical that problem followed plug on #1. Replace it; Something of a smoking gun there. Illogical that swapping #1 plug created problems with two other plugs on a mag that previously tested fine, unless there is a wiring problem, where the bad plug is causing the spark to jump to a different wire. I would want more testing. My next step would be to put an ohm meter on the plug leads. High resistance can cause spark jumping across wires. Also would check resistance of all 12 plugs. 1K is optimum.

Need more info on the chart. Not sure what the delta is from.

Larry

[BobTurner]

I think your ‘note added’ is a key clue. Difference between in flight and run up check is the volume of air moving thru the cowling. I’d be looking at your harness, where air induced movement may have created internal breaks or shorts.

[PerfTech]

... I saw this thread, and thought this may be a good place to post this potential issue
before it happens to someone in the air. Some ignitions, electronic, and computer
based, (as in some automotive type ECUs) Will throw out one random spark when
switched on. As a rule this usually isn't a big problem, but under certain conditions
it can be. If the throttle is in idle position it is less likely to happen, but if it is much
above idle the fuel system is feeding fuel and unburned air into the engine and loading
up the muffler and exhaust system with this volatile mixture. If your ignition is one that
throes this random spark, it can ignite this mixture inside the muffler, in essence making
your muffler into a bomb, and potentially putting you and your aircraft in harms way.
You may wish to investigate this further if you are not using magnetos, or have an
aftermarket system installed. A good practice is to try any action of this type on the
ground a couple of times, prior to doing it while airborne. This scenario is fresh in my
mind, as it recently happened at my home airport to a fellow with his RV-10. This
resulted in some considerable damages to his aircraft, muffler, lower cowl, and a
small fire. Needless to say it would have been frightening at best were he airborne.
Stay Safe, Allan--

[Flying again!]

Originally Posted by lr172

Suggest more testing. Quite logical that problem followed plug on #1. Replace it; Something of a smoking gun there. Illogical that swapping #1 plug created problems with two other plugs on a mag that previously tested fine, unless there is a wiring problem, where the bad plug is causing the spark to jump to a different wire. I would want more testing. My next step would be to put an ohm meter on the plug leads. High resistance can cause spark jumping across wires. Also would check resistance of all 12 plugs. 1K is optimum.

Need more info on the chart. Not sure what the delta is from.

Larry

Thanks for the comments. The delta is the difference between the CHT/EGT of each cylinder from the value when both mags are on versus the value for either Left or Right mag alone. So for cylinder 1 on right mag the EGT is 50 deg higher than running with both mags and 9 deg lower when running on left mag.

[Flying again!]

I replaced the suspect plug and am waiting for the weather to improve so I can fly and see if that helps.

If the problem is the harness, I don’t understand why the left mag ran smoothly during the previous flight. Nothing in the harness was touched or changed.

I’ll post the results of the next flight, hope both mags run smoothly.

[rv8ch]

Originally Posted by Flying again!

I replaced the suspect plug and am waiting for the weather to improve so I can fly and see if that helps.

If the problem is the harness, I don’t understand why the left mag ran smoothly during the previous flight. Nothing in the harness was touched or changed.

I’ll post the results of the next flight, hope both mags run smoothly.

I had a harness problem - and it was very difficult to track down. Slight movement of the cable would cause it. After finding it and fixing it I'm really amazed at the increase in smoothness.

I would not discount the harness.

[lr172]

Originally Posted by Flying again!

If the problem is the harness, I don’t understand why the left mag ran smoothly during the previous flight. Nothing in the harness was touched or changed.

Nor do I, hence the recommendation for more testing. Intermittent problems like this are tough to track down and usually more testing is required for a pattern to emerge.

Larry

[clam]

This doesn't help you troubleshoot per se, but it is an inexpensive and nice replacement anyway ... I was trying to troubleshoot some ignition issues and it was recommended to me to try carbon core wires (Taylor # 60651 from Summit Racing) and double check harness security. I did both by just replacing the wires. Inexpensive, easy job that gave me new wires and the issue went away. Maybe I got lucky.

[Flying again!]

I replaced the “suspect” plug with a new one (top plug on number 1) and went flying. With that one change all cylinders had an increase in EGT instead of only 3 cylinders last when on the left mag.

The first table is the previous flight where the engine was very rough on left mag.

The 2nd table is after replacing the top plug on #1 cyl. The right mag was perfectly smooth running. The left was slightly rougher but no missing or bad vibration.

The next thing I may do is change the wires as clam suggested. At this point it is running good enough on the left mag.

TJ