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  #11  
Old 06-07-2021, 11:39 PM
PCHunt PCHunt is online now
 
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Bought two today, I'll follow up in a day or so.

Thanks!
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  #12  
Old 06-08-2021, 07:07 AM
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Bill.Peyton Bill.Peyton is offline
 
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Don't get distracted by trying to mask an issue. If one mag does not exhibit this issue and the other does, and it did not do this before, then it is probably something with the mag and associated wiring and hardware. If you have exhausted all the external issues, then pull the mag and have it inspected. BTW, check your engine to air frame ground strap.
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  #13  
Old 06-13-2021, 11:17 PM
PCHunt PCHunt is online now
 
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Updating progress:

For Bill.Peyton, the noise got noticeably worse with the P-lead disconnected at the mag.

For bjdecker: Great Idea, thanks! I tested the center conducter on 4 leads on the bad mag, and 3 leads were at about 2 ohms, and steady. The 4th lead was 42 ohms, then when I intentionally moved the lead around, the resistance jumped all over the place! I have made up a new lead and installed it.

An Avionics Tech at my airport (NZAR) suggested that I test the shield on each lead as well, by taking the lead off the spark plug, then see if the shield goes to ground. Again 3 were OK, one was open. It turned out that the ferrule holding the lead into the mag cap had come loose. I trimmed the spark plug lead, and reassembled with a new ferrule.

So, two issues found, but due to weather, haven't been able to do a flight test.

Thanks for the great suggestions.........
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  #14  
Old 06-14-2021, 07:14 AM
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Bill.Peyton Bill.Peyton is offline
 
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The fact that the noise increases when the p lead is totally disconnected is could be an indication of an engine grounding issue.



BTW, the p lead should be a shielded wire. The shield should be grounded at BOTH ends, the mag and the switch. The p lead shield should not be grounded to the central aircraft ground bus.



You should verify that your engine has an independent ground strap to the airframe and the connections are clean and proper.


It does sound like you may have found your issue with a broken shield on one of your ignition wires..
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  #15  
Old 06-14-2021, 07:24 AM
PCHunt PCHunt is online now
 
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Hi Bill, I respectfully disagree about grounding the P-Lead shield at both ends. Everything I can read on the issue, including Mr. Nuckolls, says that the shield should be grounded only on one end, usually the Magneto end.

I have checked my engine ground cable, which goes from the engine to the airframe, and it appears and tests good.

If my test flight still shows a problem, I will ground both ends of the P-Lead shield, but IMHO, that's not the problem.

Testing will tell the tale.

BTW, what is the logic for not grounding the shields to the aircraft central ground? My shields are grounded only at one place, on the magneto, at the screw provided for the purpose.
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Last edited by PCHunt : 06-14-2021 at 07:33 AM. Reason: Add info
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  #16  
Old 06-14-2021, 07:46 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by PCHunt View Post
Hi Bill, I respectfully disagree about grounding the P-Lead shield at both ends. Everything I can read on the issue, including Mr. Nuckolls, says that the shield should be grounded only on one end, usually the Magneto end.

I have checked my engine ground cable, which goes from the engine to the airframe, and it appears and tests good.

If my test flight still shows a problem, I will ground both ends of the P-Lead shield, but IMHO, that's not the problem.

Testing will tell the tale.

BTW, what is the logic for not grounding the shields to the aircraft central ground? My shields are grounded only at one place, on the magneto, at the screw provided for the purpose.
The p lead is noisy and you want to use the shield to go directly back to the mag to self-cancel, when grounded. One end of shield should connect to the mag ground screw and the other to the other pole on the mag switch.

That is best practice and would be surprised if knuckles doesn’t recommend this.

Larry
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Last edited by lr172 : 06-14-2021 at 07:50 AM.
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  #17  
Old 06-14-2021, 08:05 AM
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rv8ch rv8ch is offline
 
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Quote:
Originally Posted by lr172 View Post
The p lead is noisy and you want to use the shield to go directly back to the mag to self-cancel, when grounded. One end of shield should connect to the mag ground screw and the other to the other pole on the mag switch.

That is best practice and would be surprised if knuckles doesnít recommend this.

Larry
He does recommend connecting the shield at both ends, but easy to misunderstand it the way it's written:

http://www.aeroelectric.com/articles...tchOptions.pdf

Quote:
Originally Posted by BobNuckolls
Note that I show shielded wire between the magnetos and the magneto switches. Spark plug wires and magneto p-lead wires are the ONLY wires in the airplane which are ALWAYS shielded. Further, p-lead shields should be grounded to the airframe/engine only at the engine end. The shield is used to provide a ground for the "GRD" terminals at the switch but no other connection to the shields should be made at the instrument panel end.
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Last edited by rv8ch : 06-14-2021 at 08:09 AM.
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  #18  
Old 06-14-2021, 08:06 AM
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bjdecker bjdecker is offline
 
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Attached, Aeroelectric drawing..:

The P-lead is a single conductor, shielded wire, and the shield should be grounded at "both ends" -- magneto, and the GRD pole on the keyswitch -OR- equivalent ground on ignition switch.
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  #19  
Old 06-14-2021, 08:35 AM
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rjcthree rjcthree is offline
 
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Default Completes the circuit, not grounding both ends

The diagram allows the grounding of the p lead back to the engine, what I believe to be the correct circuit path. Technically itís NOT grounded at both ends, there is no tie to the airframe ground at the switch side.
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  #20  
Old 06-14-2021, 08:47 AM
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bjdecker bjdecker is offline
 
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Quote:
Originally Posted by rjcthree View Post
The diagram allows the grounding of the p lead back to the engine, what I believe to be the correct circuit path. Technically it’s NOT grounded at both ends, there is no tie to the airframe ground at the switch side.
Of the two GRD terminals on the ACS keyswitch, the center GRD pin (the one with the STAR in the schematic) is attached to ground ALL the time.
The GRD terminal next to R terminal (Marked with an ASTERISK) is only connected to ground when the key is in the "START" position.
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2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.

Last edited by bjdecker : 06-14-2021 at 08:54 AM.
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