PMag Issue (final diagnosis - bad spark plug)

[krw5927]

Same here. 113 Pmag, ran rough. Changed plugs, still rough. Sent unit and plug wires in for testing, they said all was fine. Reinstalled, still rough. Sent back again, replaced the board for $$$$. Immediately sold the unit and haven't looked back since.

[dweyant]

So here is what I've tried to far.

1 - Replaced all 8 plugs with new ones.
2 - Checked timing on both mags
3 - Checked resistance of plug wires on #2 cylinder (.5 ohms)
4 - Made sure all of the spark plug wires are properly seated

Any other suggestions?

I'm thinking next step is to pull the mags and send them back for service?

-Dan

[dweyant]

One other thing, that may or may not be related.

On the two flights that I've done since I got the plane back from paint, my headset is breaking squelch. Not all of the time, but enough to be annoying. Not sure if/how it could be related, but thought it was worth mentioning.

-Dan

[Ironflight]

Originally Posted by dweyant

So here is what I've tried to far.

1 - Replaced all 8 plugs with new ones.
2 - Checked timing on both mags
3 - Checked resistance of plug wires on #2 cylinder (.5 ohms)
4 - Made sure all of the spark plug wires are properly seated

Any other suggestions?

I'm thinking next step is to pull the mags and send them back for service?

-Dan

You might check those plug wires again - the P-Mag manual calls for 180 Ohms per foot of plug wire - so if you really only have .5 ohms on each of the cylinder #2 wires, you?ve got something anomalous going on.

[N520TX]

Check those wires again. Your comment about "my headset is breaking squelch" is exactly what happened to me a couple yrs back. One of my plug wires had just decided it had done enough work. The resistance ohm'd out higher than expected. I replaced that one wire and all was quiet again. I then replaced all 4 ... then the other 4 this past annual. They had about 600 hrs of operation on them.

[lr172]

Originally Posted by dweyant

One other thing, that may or may not be related.

On the two flights that I've done since I got the plane back from paint, my headset is breaking squelch. Not all of the time, but enough to be annoying. Not sure if/how it could be related, but thought it was worth mentioning.

-Dan

That is symptomatic of a bad ignition wire or plug, amongst other things. Make sure that your plug wires are fully seated on the Pmag. I have seen several posts here, where they have backed off. There is not positive lock and they can creep off.

Larry

[pilotkms]

i have dual Pmags i bought in the early stages of my build (no warranty), but had only 50 hours of run time on them. during runup one of them dropped 200rpm rather than the normal 75 to 100 rpm. i changed the plugs just because but i didnt check the wires as i didnt think they would go bad in just 50 hours. talked with Brad and he had me check the EGTs. normal for mine was 1000 for each cylinder. when i switched to 1 mag #3 dropped to 900. i swapped the plug wires with #3 & #4 at the coil and now #4 dropped to 900. this indicated to me that the coil was bad and i was operating on 7 plugs not 8. confirmed this with Brad, and ordered 2 new coils, 1 to install and 1 for the shelf, at $110 each. PLUS shipping of course. seemed reasonable to me. i like spares, and Brad's service was excellent. got them 2 days later and had it installed in about an hour, and im no A&P. EGTs now normal for all 4 cylinders, both Pmags. if i never need the spare i'll be selling it here at a discount. so try the wire swap on the same bank of plugs (see the manual) and see if yours does the same.

[rapid_ascent]

Relating to Paul's resistance comment could your meter be on the Kohm scale implying 500 ohms not 0.5 ohms?

[dweyant]

Tried a few more things this morning.

Replaced the coil on the left mag. Engine still runs rough, and now the EGT,s on#3 drop off as soon as I run on just the left mag.

Is it time to send them back to EMag and have them look them over?

-Dan

[tim2542]

Keep in mind this is a wasted spark system, one coil fires two plugs so if it were a coil problem you?d most likely see in on both cylinders served by a coil, 1&2 and 3&4 are your companion cylinders and will share a coil.
I?d study your EGT?s more closely and see if you can pin it down to a cylinder or pair of cylinders, then move plugs and or leads around until you pin it down or eliminate these high tension parts.
Good luck
Tim Andres