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Old 03-25-2012, 02:19 PM
KayS KayS is offline
Join Date: Jul 2009
Location: huntsville/alabama
Posts: 130
Default p-mag ignition wire resistance

Hi All,

i fabricated one ignition wire for my p-mag today. i did it like the manual told me and everything was looking good. but then i measured a resistance between the two coils at about 0,5 kilo ohms. i expected something near zero. do i miss here something?

Kay Stecklum
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Old 03-25-2012, 04:48 PM
lostpilot28's Avatar
lostpilot28 lostpilot28 is offline
Join Date: Nov 2006
Location: Boise, ID
Posts: 1,095

From the P-mag installation manual - "Each lead should produce approximately 180 ohms of resistance per foot of plug wire".

How long is the wire you made? If it's 2-1/2 feet long, then 500 ohms would be good. I'm assuming you mean .5 k-ohms, BTW.
Sonny W
Boise, Idaho
RV-7A Flying!
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Old 03-25-2012, 04:52 PM
KayS KayS is offline
Join Date: Jul 2009
Location: huntsville/alabama
Posts: 130

ups... seems that i didn't read that whole manual. mine is about 2 feet long... that explains everything. thank you.

Kay Stecklum
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Old 03-25-2012, 10:04 PM
rwtalbot rwtalbot is offline
Join Date: Feb 2006
Location: Sydney, Australia
Posts: 230
Default Check them every year!

As a suggestion, write down the figures for each lead and check them every year at annual. The leads can get moisture inside and corrode over time. I wiggle the ends of each lead with the multimeter attached to look for any looseness.

This year I had two leads fail (3rd annual and just over 300 hours TT). I had noticed a very slight intermittent miss at idle. Two new leads later and the engine now starts really well - I had not noticed any degradation. The miss is gone too.

Interestingly, the failed leads were both upper plugs. I fly a fair bit of IFR and they have definitely had some water in the front. Corrosion was evident. I am investigating methods of obtaining a slightly better plug lead or use of a dielectric grease.


RV 7A - Flying
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