Dual PMags: RPM drop during left/right mag check

[Tankerpilot75]

I just completed addressing several squawks (nothing FWF) and went to do a check flight after bringing the aircraft home. Both PMags dropped 200 RPM doing pre takeoff mag check at around 1850 rpm. Since I had recently upgraded my old GRT EIS motherboard to accommodate the need for greater Tach rpm sensitivity due to electronic ignition and because I was only going to orbit the field - I accepted the higher drop to see what happens in flight.

First flight every thing looked normal (CHTs, EGTs, Oil Pressure and Oil temperatures). Takeoff/climb to 3,500 feet felt normal. After three trip around the airport, I landed and taxied back to the ramp. Did another mag check. Once again there was a 200 rpm drop - both sides.

I again took off and started climbing to 5,500 feet. Airplane felt sluggish in climb. Monitoring engine data saw cylinders 2,3 &4 normal (2&3 CHTs between 380 to 395, #4 around 415 with EGTs all around 1190. Number 1 cylinder’s CHT however was dropping while its EGT closely aligned with the three other EGTs. I returned, landed and while taxiing to my hangar #1 cylinder CHT began to rise back towards 300 degrees. Another mag check - same 200 rpm drop with another mag check.

I would normally think I had a #1 CHT probe issue or cylinder spark failure issue but with the excessive mag check rpm drop on both sides it seems likely something else. The PMags were just installed on my rebuilt engine in March and ran great on the trip back to OKC from OSH. (Had a prop strike at Airventure last year). I only have eight and ahalf hours on the engine since inspect/rebuild and it ran smooth on the trip home.

Called EMag and talked to the service technician about the issue. He suggested I go through the troubleshooting guide to better identify the problem. I will do this next week with the help of an experienced PMag owner but in passing I did ask the tech what he thought was likely the problem. He said “spark plug failure.”

My questions:
1. Has anyone else experienced a similar situation?
2. The lower rpm drop on the mag check was on both sides. Can a single plug failure cause both sides to read low on a run up mag check?
3. If a #1 cylinder’s plug failed and caused the dropping/declining CHT wouldn’t it’s EGT also drop?

Brain trust please explain.

 

[Avanza]

Plug failure

If one plug fails, you get incomplete combustion in the cylinder. That may lead to lower CHT and a higher EGT if the unburned fuel is burned in the exhaust.
I'm not familiar with P-mag so I can't comment on the rpm drop indicated.
I would swith plugs with an other cylinder and se if the offending indication moves to the other cylinder.

Good luck

 

[Ironflight]

It coudl be as simple as the plug wire not making solid contact with one plug. The automotive plug boots have a tendency to trap air, and the inexperienced can think they have seated the plug wire “clip” on the plug, but really only made contact with it, and vibration, pressure changes, etc can make it have intermittent contact. Go around to all 8 plugs and make sure that the wires are positively clipped on to the plug - its an easy check….

 

[Walt]

Why do people decide to take off with known issues, "hoping" that whatever is wrong will somehow miraculously fix itself?

 

[Tankerpilot75]

Why do people decide to take off with known issues, "hoping" that whatever is wrong will somehow miraculously fix itself?

Walt, I wanted to look at CHTs, EGTs, RPM and MP all under load. I respect your opinion and concern but I felt it was safe. I never left the area of the airport and stayed within gliding distance. Your opinion differs and that’s okay.

 

[John Tierney]

When checking the spark plug wire connections, verify whether the spark plugs have screw on terminal ends. If they are screw on sometimes they come loose and can cause spark issues. I try to buy the solid terminal end spark plugs.

 

[Tankerpilot75]

When checking the spark plug wire connections, verify whether the spark plugs have screw on terminal ends. If they are screw on sometimes they come loose and can cause spark issues. I try to buy the solid terminal end spark plugs.

They are the solid end plugs. Thanks for your input.

 

[Walt]

Walt, I wanted to look at CHTs, EGTs, RPM and MP all under load. I respect your opinion and concern but I felt it was safe. I never left the area of the airport and stayed within gliding distance. Your opinion differs and that’s okay.

My point is this was an unnecessary risk, you already knew something was wrong before you took off, no need for anymore data than that.

 

[gear1]

200 rpm drop on P-mag check

With electronic ignition the test is almost as much a mixture check as an ignition health check as the P-either works or it doesn't work. The fact that you are getting the same rpm drop with either P-Mag off indicates that both are fine, and the spark plugs are fine. You should get an EGT increase when either P-Mag is turned off, and at about the same amount of increase.
If you are doing your p-Mag checks at full rich, try leaning for max rpm, starting at about 1700 rpm. Leaning will increase the rpm to 1800 to 1850 rpm. After leaning check the P-mags in the normal manner; i would wager that your rpm drop will be less than 50!

 

[Richard Connell]

With electronic ignition the test is almost as much a mixture check as an ignition health check as the P-either works or it doesn't work. The fact that you are getting the same rpm drop with either P-Mag off indicates that both are fine, and the spark plugs are fine. You should get an EGT increase when either P-Mag is turned off, and at about the same amount of increase.
If you are doing your p-Mag checks at full rich, try leaning for max rpm, starting at about 1700 rpm. Leaning will increase the rpm to 1800 to 1850 rpm. After leaning check the P-mags in the normal manner; i would wager that your rpm drop will be less than 50!

Indeed. On my rv7 one light speed, one Pmag, the indication I was looking for at mag check was EGT rise. Minimal to no RPM drop at all.
If I had any RPM drop something was up. Usually fouled plug, but once was swapped leads at the coils after an annual.

 

[Tankerpilot75]

If you are doing your p-Mag checks at full rich, try leaning for max rpm, starting at about 1700 rpm. Leaning will increase the rpm to 1800 to 1850 rpm. After leaning check the P-mags in the normal manner; i would wager that your rpm drop will be less than 50!

Thanks, this is a great idea!

Since I’m still in the break-in process I’ve been running really rich for just about everything. My trip back to OKC was 24/24 with FF at 12 gal/hr to ensure CHTs were kept as low as possible (Popular Grove guidelines). I did check the top spark plug on #1 after parking in the hangar and it looked clean but didn’t want to pull the bottom without help (new three blade prop makes removing bottom cowling harder).

Tuesday I plan to remove and replace all the plugs (tech recommendation) and follow the EMag Troubleshooting Guide to identify the best solution. A friend with PMag experience is going to assist. Nice thing about replacing these plugs is they’re inexpensive.

If rpm drop after plug replacement and following the troubleshooting guide returns to the 50 - 80 rpm drop I expected then I’ll definitely follow the procedure you’ve recommended. Electronic ignition is new to me and I’m seeing some subtle differences in engine operation and performance.

 

[Walt]

Check timing while you’re at it, CHT’s are awfully high, Suggest retarding 5 or 10 deg from ‘0’. You want to keep it cool during break-in.
Adjust idle mixture.

 

[Tankerpilot75]

Walt,

Since PMags are timed at TDC (not 25 BTDC), what you’re suggesting (timing 1 to 6 degrees after TDC) is in accordance with the EMag manual’s retardation suggestion. It will minimize gear play, help prevent a reverse start, and allow for a less aggressive operating range. I think the rings are close to being seated based on stabilizing oil consumption but I’ve been warned not to run LOP until there is at least 25 hours on the engine. Keep it rich and cool.

It further warns that low mass propellers such as my MT can decelerate rapidly during start as it passes through TDC with combustion potentially causing the prop to catch and spin backwards. Again another reason for timing 1 - 6 degrees after TDC.

Lots of things to think about with this change from Slick magnetos to PMags. I guess run lean on the ground and rich from takeoff to landing.

 

[rv8ch]

Jim, if you don't have one, I'd also recommend getting an EICommander or EngineBridge to see what your pmags are doing. It also makes it very easy to set the timing slightly differently.

Are you comfortable that the little MP hoses are connected right? I've read of cases where they fall off...

I have also personally experienced spark plug wires that were bad. This showed up in my headset as very strong static. Best plugs I've used are the solid tip $1.75 NGK BR8ES from Rock Auto.

 

[Tankerpilot75]

I have also personally experienced spark plug wires that were bad. This showed up in my headset as very strong static. Best plugs I've used are the solid tip $1.75 NGK BR8ES from Rock Auto.

That is what’s in there right now. BTW, they’re now $4.59 a plug here in OKC.

 

[lr172]

A large RPM drop, assuming no individual cyl stops firing (observe EGT rise on all 4), generally points to excessive ignition timing advance. If both create a 200 RPM drop, then both are likely too far advanced. Also explains the higher CHTs and low EGTs and sluggish performance. 1190 is quite low for EGT at full power unless filthy rich. It is not bad plugs. They either spark or they don't and you will know when they don't during a mag check (EGT falls off and engine gets rough)

Step one should be to re-time pmags. Then check for blockage in vacuum tubes for Pmags.

 

[Carl Froehlich]

Walt,

Since PMags are timed at TDC (not 25 BTDC), what you’re suggesting (timing 1 to 6 degrees after TDC) is in accordance with the EMag manual’s retardation suggestion. It will minimize gear play, help prevent a reverse start, and allow for a less aggressive operating range. I think the rings are close to being seated based on stabilizing oil consumption but I’ve been warned not to run LOP until there is at least 25 hours on the engine. Keep it rich and cool.

It further warns that low mass propellers such as my MT can decelerate rapidly during start as it passes through TDC with combustion potentially causing the prop to catch and spin backwards. Again another reason for timing 1 - 6 degrees after TDC.

Lots of things to think about with this change from Slick magnetos to PMags. I guess run lean on the ground and rich from takeoff to landing.

Jim,

- What engine are you running - angle head or parallel valve?
- Standard compression?
- Do you have the pMag jumpers in?
- Are you confident of your timing process?

I would assume at 25 hours you need not be running constantly overly rich. Also consider LOP drops CHTs, not increases them.

Carl

 

[Tankerpilot75]

Jim,

- What engine are you running - angle head or parallel valve?
- Standard compression?
- Do you have the pMag jumpers in?
- Are you confident of your timing process?

I would assume at 25 hours you need not be running constantly overly rich. Also consider LOP drops CHTs, not increases them.

Carl

Parallel valve, standard compression, PMag jumper in, no I’m not confident in my timing process which is why I had Myers Aviation do the PMag install and why I’m having a friend help me with the troubleshooting. However I can and have studied the installation manual and troubleshooting guides in detail and am just regurgitating what I’ve read.

I agree LOP should give cooler CHTs however when breaking in new rings it’s better to use fuel to keep temperatures low until break in is complete - or so I’ve been told.

 

[Carl Froehlich]

Parallel valve, standard compression, PMag jumper in, no I’m not confident in my timing process which is why I had Myers Aviation do the PMag install and why I’m having a friend help me with the troubleshooting. However I can and have studied the installation manual and troubleshooting guides in detail and am just regurgitating what I’ve read.

I would not do anything until verification of timing. Don’t assume any shop remembers to not time these like a mag.

Carl

 

[bruceh]

I don't know what else I can add to this thread, but on my dual P-mags I never see much more than an 80 RPM drop.
Do the easy stuff first. Turn on the power and you should be able to see the Green LED light up when you are at (or very near) TDC on each P-mag. Both should light up in synch with each other. Otherwise you have a timing divergence, which could make a larger mag drop.
Check the resistance of the plug wires. Check the plug connectors are seated properly. Check the plugs. Check the wiring (jumper in, ground and power) to the P-mags.

 

[flyvans.com]

we have dual pmags and never see more than 110rpm drop (L & R identical)
on a TMX-IO-360

for the first 500hours we were running one PMAG on the A curve and otherwise at defaults (due to wanting to be able to read the serial data) and one traditional mag with the standard 25° timing / aviation plugs etc... When we ordered the engine, Pmags were quite new and went through some of their early teething problems/growing pains, so wasn't comfortable to go "all in" at the time. What suprises me, in retrospect, the A-curve without any tweaking, should actually have cause more temperature etc... issues due to aggressive timing advance, yet this was never a problem.

Then, when we reached the 500h overhaul point of the mag, we replaced the Mag with a second PMAG. And initially had configured both PMags on the A-curve (without jumper in) so that RS232 readout would still be available.
Engine was still running fine, however not as smoothly as before and at in average, higher temps.
After talking to Brad at Emagair extensively, trying various configurations via serial programming/EICAD, still on the A-curve, finally decided to call it quits and just put in the Jumpers / went with both PMAGs to the B-curve (hence no more serial monitoring possible), and "clocked" it with the prop 1° after TDC. Ever since have been very happy with operation and temps. Maybe a tiny bit more fuel flow than before, other factors being equal, but at an irrelevant magnitude.

One big disadvantage via the serial programming / A-curve route is the fact that the serial programming is not as straight forward (software compatibility, software bugs, usb-to-serial adapter issues, wiring etc...) and the fact that any kind of maintenance later on, replacement etc... will need to make sure that the correct settings are reintroduced, otherwise you may run into issues. It wasn't available at the time, but if one would want to run the A-curve for some reason, the EIcommander and similar devices are definitely a good idea.

Performance wise, the B-curve is still plenty better than the traditional Mags and we have hardly seen a difference to the situation before with the mix of Pmag and Mag. Maybe a tiny bit higher fuel flow and marginally higher temps for the same speeds now, compared to before.

 

[Tankerpilot75]

PMag Issue Update

Yesterday my friend Dan and I went through the troubleshooting process following the EMag guide. Left PMag spark seemed weaker when doing pull through - but wasn’t totally sure we were getting a good ground on bottom plugs because of space/wire limitations. When it came time to validate and reset the timing the left PMag would not enter setup mode. The LED indicator light stayed steady red no matter how hard we blew or (alternative method) squeezed the tube. Right PMag behaved as expected with strong spark.

Pulled PMag and will send back to EMag for warranty evaluation/repair. Could be a case of infant mortality - only 10 hours on engine/PMags since rebuild/PMag installation. It happens! Will keep folks updated.

 

[Tankerpilot75]

Issue resolved

Pulled left PMag after following trouble shooting guide and mailed it USPS last Wednesday. They received it Friday morning at 9:34 am according to the signed receipt. They repaired the PMag and immediately sent it back via overnight UPS. Received it Saturday morning! Wow, that’s fast service!

I’m told the problem was a tight bearing which was replaced. Why a tight bearing would cause my problem entering setup mode - who knows but today I reinstalled the PMag, it smoothly went into setup mode without any issues and I was able to retime the PMag - this time around 2 degrees past TDC.. Sure is tight back there!

Brad was fantastic to work with and helped me better understand how these things work and what a “wasted spark system” is, how they operate, its advantages, and the timing flexibility they offer. Still have an issue with what appears to be a CHT probe on one cylinder but at least that was easier to diagnose. Gotta love EMag Ignitions, Inc.

 

[mike newall]

I first met Brad way, way back at Sun n Fun when he was selling E-Mags. I said they looked great, but our LAA wouldn't accept them as a dual install if they needed power. That is when he said he was developing the P-Mag.

Our 7 was in build and had a new ECI engine with LASAR. We heard that the writing was on the wall for that system and we became the second in the UK to install dual P-Mags and we first flew in 2010.

We were required to monitor and report any problems, but there were none.

Some teething problems were reported on here, but Brad seemed to pride himself in swift turnround and still does.

We had a slight misfire on departure 3 years ago, couldn't replicate it, mags had done 600 hours. Spoke to Brad and he said send them for inspection and check. Even though we are in the UK, the turnround was about a week ! Biggest problem I had was convincing customs that they were mine and already duty paid !

I have enjoyed helping Brad out on his stand at Sun n Fun a few times for the odd half hour. Always good to be able to give an actual user report - although I normally said - give him 16 numbers and an expiration date first and then we will tell you all the good stuff !

Great company