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  #1  
Old 07-19-2022, 06:50 PM
bruceh's Avatar
bruceh bruceh is offline
 
Join Date: Mar 2008
Location: Ramona, CA
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Default One of my P-Mags lost its timing

A bit of background:
My RV-9A has dual P-mags. Airplane is approaching 1000 hours of trouble free electronic ignition usage.
I did my condition inspection last month (June 2022) which involves inspecting the bearings on the P-mags for "excessive play". Mine both had what I would call excessive play (one had a lot, the other was minimal, but still was moving around the axis of the bearing).
I sent both of them back to E-mag for the flat-rate checkup. Got them back, installed them as usual - set the timing, reset the proper advance curve, and all was well again.
I flew about an hour and had no issues, then before another local flight I had a
mag-check failure and the internal generator was also not powering the ignition properly below 1000 RPMS. Plug wires were checked and had good resistance readings. Sparkplugs are new NGK BR8ES. The EGT's/CHT's didn't point to any particular cylinder going cold, just ran really rough and dropped from 1700 RPM to 1200-1400 RPM during the mag check.
I checked the connections, wires and timing which all looked good.
I did some more run ups and was unable to get the internal generator test to pass. I pulled both P-mags off and swapped them. Retimed again and then did more run ups. This time the problem moved sides, so I knew it was definitely the one P-mag.
I sent this off to E-mag again, and they confirmed there was an electronic issue. They swapped out the internals and sent it back at no charge (great service by the way). I reinstalled this P-mag and went through all of the usual timing steps. I went flying on Saturday and everything was working great again. No issues with the mag check or the internal generator tests.
Today I flew up to Corona to pick up some items from Aircraft Spruce. The departure run up was perfect with no issues. I landed, got my will-call order and had some breakfast at the Cafe, I then fired up the airplane for the short trip home.
The engine failed the mag check. When I selected the Left P-mag (this one is not the one that was recently re-repaired), the engine would back fire and quit if just left on the left side. I got the airplane over to the maintenance shop on the field and took off the cowling. I was able to talk with Brad at E-mag and he gave me a number of suggestions. The first one was to confirm that the timing was still set.
I borrowed a mirror (and also used my cellphone camera to video the LED on the Left P-mag) to see if the LED at TDC was Green like the other P-mag. It was steady Red all the way through 720 degrees of prop rotation.
I set the timing on the left P-mag and it went back to being in sync with the other P-mag. Both LED's flash green at TDC.
Very strange!
I did another run up and mag check and all was good again. I reinstalled the cowling and did another extensive set up run ups before departing back to Ramona. No issues in the flight home.
Now I'm trying to figure out what could have caused this problem. Reading other threads on P-mags losing timing call out some potential culprits. I'm running the most current Firmware version #41, so it should have the latest fix for losing timing on powering up during the engine running. I don't use a trickle charger, so that isn't pulsing any of the electronics. I have blast tubes on the P-mags and have not had any overheating issues in the past (but it has been hot lately here). The EIC display showed both P-mags in sync and advanced at the same curve. I'm running the recommended timing for my IO-320 and I've confirmed that both P-mags have the same timing curves set.
Oshkosh awaits and I'm wondering if I can depend on these to get me there and back without issues.
What else should I investigate?
Brad suggested bypassing the EIC and just putting in the jumper for the A curve timing. He also suggested testing without the ground wire from the key switch in place to see if there might be a grounding issue inside the key switch that might be disabling the P-mag.
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  #2  
Old 07-19-2022, 07:24 PM
pa38112 pa38112 is offline
 
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The last two suggestions both sound like good suggestions to me.

Is the problematic p-mag the same one that had to be sent back twice?

Are you sure the mag did not rotate slightly on the accessory housing?
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  #3  
Old 07-19-2022, 07:30 PM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by bruceh View Post
SNIPÖ
Brad suggested bypassing the EIC and just putting in the jumper for the A curve timing.
This.
Carl
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  #4  
Old 07-19-2022, 07:37 PM
KatanaPilot KatanaPilot is offline
 
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Location: Locust Grove, GA
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Default

I have had several problems with my pMags similar to yours. The EIC has been invaluable in showing timing divergences.

Brad has also suggested disconnecting the EIC, which I will not do.

I ended up buying a new pMag which solved my problems.

I have a lot more confidence in the accuracy of the EIC than I do in the reliability of the pMags.
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  #5  
Old 07-19-2022, 08:05 PM
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bruceh bruceh is offline
 
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Quote:
Originally Posted by pa38112 View Post
Is the problematic p-mag the same one that had to be sent back twice?

Are you sure the mag did not rotate slightly on the accessory housing?
No, it is the other P-mag, but it is in the same location (left side). I put them back in the same positions after the first service, then swapped them so now the one that was sent back twice is in the right side.

No slippage that I could tell. They are on tight.
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  #6  
Old 07-19-2022, 11:31 PM
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rv8ch rv8ch is offline
 
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Is there any chance that the 12v power could have been applied while the mags are grounded, accidentally putting the mags into setup mode? According to the manual, solid RED means that the device is in setup mode.

This is why I have a completely separate switch to apply 12v to the mags when I want to move to setup mode.

Quote:
Originally Posted by https://emagair.com/wp-content/uploads/2017/08/Manual-LC114v28.pdf
If the p-lead was grounded PRIOR to power up and REMAINS grounded, the ignition will light the LED steady RED or steady GREEN (after the step 2 color burst). The color will depend on engine position relative to the ignition index. If the p-lead was not grounded, the LED will go dark after the color burst. Setting timing and the rules for setup mode are discussed in more detail in the manual.
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  #7  
Old 07-20-2022, 10:03 PM
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bruceh bruceh is offline
 
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I took off the cowling today to replace my failing EGT probe on Cylinder #4. The failing probe was my reason for flying up to Corona and Aircraft Spruce to pick up a new one.

I checked the timing again with both P-mags flashing the Green LED at TDC.
I Ohm'ed out the key switch and everything there checked out.

Cowl back on, I did several more run ups successfully, then went around the pattern here several times with no issues. The engine is running good and is smooth. The EIC shows a solid 2.0 on the divergence and everything I could see with the data was as expected. Back on the ground I did another start and run up sequence with no issues. I have no other reason to think there is anything that has actually failed with the P-mag.

I guess Oshkosh is on for me! I'll be taking plenty of tools and if needed E-mag will be there to help do any maintenance.
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  #8  
Old 07-21-2022, 08:49 AM
rapid_ascent rapid_ascent is offline
 
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Bruce, Iím curious what your PMAG power switch configuration is referring back to Mickeys question. Iíve been thinking about my plan to have normally on switches which would be momentarily turned off for testing the generator. I recently saw the referenced paragraph in the install manual.
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  #9  
Old 07-21-2022, 09:24 AM
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Walt Walt is offline
 
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Quote:
Originally Posted by rapid_ascent View Post
Bruce, Iím curious what your PMAG power switch configuration is referring back to Mickeys question. Iíve been thinking about my plan to have normally on switches which would be momentarily turned off for testing the generator. I recently saw the referenced paragraph in the install manual.
Best be careful with PMAGS and 9.6 unless you change the programming to limit advance.
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  #10  
Old 07-21-2022, 10:10 AM
Bavafa Bavafa is offline
 
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Location: Sacramento, CA
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Quote:
Originally Posted by Walt View Post
Best be careful with PMAGS and 9.6 unless you change the programming to limit advance.
Walt,
I believe I am baffled by this response to the question? What is "9.6" and programming limit to the advance has to do with the type of power switch?

Quote:
Bruce, Iím curious what your PMAG power switch configuration is referring back to Mickeys question. Iíve been thinking about my plan to have normally on switches which would be momentarily turned off for testing the generator. I recently saw the referenced paragraph in the install manual
I don't mean to speak for Bruce but I am in favor of the type of switch that one can actively/easily kill the power to the PMAG. This of course can be accomplished if there is a pullable CB with the type of switch you are installing.
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