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P-Mag question. Possible misfire?

lostpilot28

lostpilot28

Well Known Member
I flew to Reno this weekend and back...nice easy flight. This is the second time I've flown down there. For the most part, the engine runs very smooth. But occasionally the engine will skip a beat. It happens very fast, and it's imperceptable if you're not paying attention.

I don't believe it's either of the P-mags. If I had to guess, I'd think it was the auto spark plugs. They've got 86 hours on them now, and I've never cleaned them or anything.

Anyone have any ideas?
 
Sonny, since auto plugs are so cheap why not put 8 new ones in. If the problem goes away....solved. Clean the old ones, put them on a tester and keep the good ones as spares.

If not, I would take a look at the harness perhaps.

PS It raises a question I have never received a practical answer to. I am a bit leery of taking my auto plugs out to look at them because I can neither replace/anneal the washers. Any practical solutions....anyone?
 
Curious what you are running for plugs. I just switch from the BR8ES to the BR8EIX Iridiums. Much more $$, but I figured still a whole lot cheaper than aviation plugs.

FWIW I seem to hear every engine I fly behind miss a beat now and then. Since I had a failure on takeoff my ears are always tuned to the sounds of 4 well timed cylinders.

As far as annealing your washers, are you talking about annealing the spark plug washer or the adapter washer? The spark plug washer doesn't need to be annealed and the adapter washers can be annealed easily with a torch and some coolant.
 
Tony,

What was the result of the switch to the more expensive plugs? Any change in CHTs? Just curious.

Ken
 
RV8R999 said:
Tony,

What was the result of the switch to the more expensive plugs? Any change in CHTs? Just curious.

Ken
Click to expand...

I installed the plugs and haven't flown on them yet. I hope to fly this morning or tomorrow and will report. I also tested my leads and (180ohms/ft) and they seem to be good.

My cheap plugs were fine. I have had one cyl (#3) that the CHT runs cooler and has a higher EGT and I wanted to eliminate the plugs as a culprit.
 
apkp777 said:
As far as annealing your washers, are you talking about annealing the spark plug washer or the adapter washer? The spark plug washer doesn't need to be annealed and the adapter washers can be annealed easily with a torch and some coolant.
Click to expand...

I have been trying to leave the adapters in and just take the auto plugs in/out to reduce the wear & tear on the engine threads. But you have a good point.
 
I flew today with the BR8EIX Iridium plugs. I would definitely say that the engine ran very smooth. Normally when I approach peak EGT, the engine stumbles uncomfortably. Today I was surprised that it was not nearly as noticeable. Unfortunately however the change did nothing for my Low CHT high EGT problem on #3.
 
missing

If this is just an occasional hiccup, consider the possibility of a valve sticking. this will occur on engines closer to tbo.
 
NDrv8r said:
If this is just an occasional hiccup, consider the possibility of a valve sticking. this will occur on engines closer to tbo.
Click to expand...

It is an occasional miss...pretty random, actually. Although at one point yesterday it happened within 10 seconds of each other. I hope it's not a sticking valve...my engine has 86 hours on it since new!
 
Temps

apkp777 said:
I have had one cyl (#3) that the CHT runs cooler and has a higher EGT
Click to expand...

Tony
Low cht, high egt sounds like energy leaving the cylinder rather than be used in the cylinder.

If this is a new development a wobble test would probably be a wise (aka the morning sickness test )

If it is normal temps, then can you do a gami lean test ? Doesn't matter if you have carb since the test is still useful for defining the fuel distribution. Maybe you are already familiar with the test, if not google is your friend :)
 
nomocom said:
Tony
Low cht, high egt sounds like energy leaving the cylinder rather than be used in the cylinder.

If this is a new development a wobble test would probably be a wise (aka the morning sickness test )

If it is normal temps, then can you do a gami lean test ? Doesn't matter if you have carb since the test is still useful for defining the fuel distribution. Maybe you are already familiar with the test, if not google is your friend :)
Click to expand...

Thanks Stan,

I am not familiar with the Gami lean test, I will look into that. This issue has been present since hour 1. I suppose it's possible that it could be a valve issue. That is on the bottom of my troubleshooting list and one of the only things left to check. I agree the indications are that the cylinder is not running as efficiently as the others.

I should probably start a new thread, although it is possibly (though unlikely) a P-mag mis-fire.
 
lostpilot28 said:
It is an occasional miss...pretty random, actually. Although at one point yesterday it happened within 10 seconds of each other. I hope it's not a sticking valve...my engine has 86 hours on it since new!
Click to expand...

Did you check your P-mag harness? You should have 180ohms/FT and when you wiggle and twist the wire there should be no change. It is possible that you nicked a wire when assembling the harness and are getting some occasional arcing.
 
Any practical solutions/ Plug removal

Steve Sampson said:
Sonny, since auto plugs are so cheap why not put 8 new ones in. If the problem goes away....solved. Clean the old ones, put them on a tester and keep the good ones as spares.

If not, I would take a look at the harness perhaps.

PS It raises a question I have never received a practical answer to. I am a bit leery of taking my auto plugs out to look at them because I can neither replace/anneal the washers. Any practical solutions....anyone?
Click to expand...

Here a VA link to an earlier G3i post on inserts and auto plug removal. http://www.vansairforce.com/community/showthread.php?t=49350&highlight=g3i

See ya @ LOE
Thomas S.
 
OK, just bought 8 new plugs. I didn't want to spring for the Iridium plugs, so I just went with the NGKs. I'll ohm out the wires this evening! Thanks for the help, fellas!
 
Hey Tony, I ohmed one of my plug wires and it came out to almost exactly 180 ohms per foot. It was 3 feet long...maybe a couple inches. It read 554 ohms.

Is the 180 ohms per foot a "maximum" value, or just what it's supposed to be?
 
Sonny,
I believe that 180 OHM is the approx resistance of the leads. I am sure it could be off be a few OHMS either way and still be fine. I think a nick would show up as a dramatic change.

I have made another flight and am convinced that the Iridium plugs are much smoother than the cheaper BR8ES. I have been able to run LOP for the first time and I attribute that to the plugs. I don't know if it would help but I think the plugs are a good choice.
 
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