pmag RPM drop

[William B.]

My IO 375 with auto plugs and leads, dual P mags, now with 36 hours.
During Mag check at 1750 rpm I get 100 rpm drop on one side and 50
on the other. Checking at Higher RPM 1850 the drop shows 80 rpm and 40 on the other. My understanding was there was to be very little mag drop with
these Pmags? Anybody with knowledge on this please comment.

[flyingriki]

Maybe Bill can check with the manufacturer and get back to us on this? I'd like to know also.
Never had any drop with the lightspeed, when it worked...

[miyu1975]

Do you have top and bottom plugs per pmag? My experience is that when bottom only I get more of a drop than top only. The bottom plugs tend to foul more. Also, be sure to lean out for ground ops. Running to rich while taxiing well foul the plugs quickly too.

[N941WR]

Originally Posted by miyu1975

Do you have top and bottom plugs per pmag? My experience is that when bottom only I get more of a drop than top only. The bottom plugs tend to foul more. Also, be sure to lean out for ground ops. Running to rich while taxiing well foul the plugs quickly too.

Ryan has some good advice.

Some mag drop is normal with the P-mags.

"flyingriki" comment regarding no mag drop on his LSI, when it worked, is probably a result of how the two different ignitions are designed. Remember, the P-mags use the cam gear to set the timing and we have found that there is about 1.5 degrees of gear lash (slop) in that setup.

Other things that could impact your mag drop is the plugs used (solid vs. threaded cap), how the wires are run (touching and engine mount), how you grounded the P-mags (engine case vs. forest of tabs), etc.

[William B.]

Thanks for the ideas, will check everything you mentioned.

[William B.]

I sent the question to EMAGAIR No response

.

Originally Posted by flyingriki

Maybe Bill can check with the manufacturer and get back to us on this? I'd like to know also.
Never had any drop with the lightspeed, when it worked...

[William B.]

I will switch tops for bottoms on each side and see if the issue follows.

Originally Posted by miyu1975

Do you have top and bottom plugs per pmag? My experience is that when bottom only I get more of a drop than top only. The bottom plugs tend to foul more. Also, be sure to lean out for ground ops. Running to rich while taxiing well foul the plugs quickly too.

[drill_and_buck]

Bill,
For a data point I have a TMXO360 with dual pmags. Each mag is wired to top and bottom.plugs I get 50-60 RMP drops on each mag at 1700 rpm

Mike

[dweyant]

Bill,

Did you ever get a response on this?

Thanks,

-Dan

[N941WR]

Originally Posted by G3i Ignition

Interesting on above "quotes"
So how far are the left and right P-mag ignitions out of sync. even on best set-up?
Spark plug terminal ends, really?

We found that even standard mags have up to ~1.5 degrees of slop in them. This can be made worse depending on how one sets the timing. (It is best to set the TDC on both P-mags at the same time. Don't ask me why but we have had customers report minor timing divergences when they are set individually.) It is nothing a pilot would ever notice but with the EICommander installed, it will pick up the difference.

Regarding the sparkplug ends; again, the EICommander has picked up a slight variation due to plugs with screw on caps.

In fact, the EICommander can tell me when my plugs are getting close to needing replacement.

To be clear, individually, you might never notice all these things, but toss in an EIC and you will "see" them. Heck, one customer kept getting Timing Divergence Alarms and once he moved the P-mag ground wires from the firewall to the engine case, they went away.