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tgrady10

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I have a new-to-me RV-4 that I did not build. I tried to pick up flight following on a post MX flight after my recent conditional, but was unreadable by ATC. After chatting with someone at the home airport and a bit of testing, it was determined that transmissions were fine at idle, but mostly static at high RPM. This was confirmed in the air, as I can throttle down and talk to ATC.

The plane has an AEIO-320 with dual P-Mags. Radio is a Flightline FL-760. I also have an old PM1000 intercom that I found to be INOP as I began the process of troubleshooting the COMM issue. I emailed PS and they do not believe that would cause the TX issues. I have a used PM1000II coming to replace the old unit though.

The relation to RPM has me thinking ignition. I sent an email to Hartzell about the P-Mags, but have not heard back. I did find the FAQ on the old P-Mag website and it mentioned spark plug wires not being seated as a potential cause. I pressed on all the wires and found one wire on the spark plug side that clicked once when pressed, and one wire on the P-Mag side that clicked twice when I pushed it in. I fired up the engine and tested the radio on the ground. It was still sending a fair bit of static at 1800 RPM when running up and transmitting on the ground. Have not had a chance to try pickup up flight following at cruise RPM though.

Does anyone have suggestions for troubleshooting steps, or past experience with anything similar?
 
Bad wires would also be my first suspect. I believe the wire kits supplied with the pmags are of marginal quality. Pull each wire off each coil terminal and each plug looking for pitting or wear from arcing. If that is the issue, you can use pliers to squeeze down the terminal arms a bit for a tighter fit. If not, the issue could be a poor connection where the terminal crimps on the wire. Many folks assembling them don’t fully understand how they work and create poor connections.
 
Another simple check is if your automotive spark plugs have the screw on caps - are those caps secure/tight. I've heard rumors that loose caps can also create radio noise. Not verified but seems plausible.
 
IMG_3210.jpegIMG_3209.jpegI think but cannot confirm that the radio was clean before maintenance. The previous owner and ferry pilot reported no issues, but I only had two way communications while at idle since taking possession in fall.

I did take off the cowl today and looked at plug wires. I found one that I think shows signs of arcing on the P-Mag side. Pictures attached. I did not have anything on hand to clean the corrosion though.
 
tgrady10 said:
View attachment 119599View attachment 119600I think but cannot confirm that the radio was clean before maintenance. The previous owner and ferry pilot reported no issues, but I only had two way communications while at idle since taking possession in fall.

I did take off the cowl today and looked at plug wires. I found one that I think shows signs of arcing on the P-Mag side. Pictures attached. I did not have anything on hand to clean the corrosion though.
Click to expand...
Looks like a lot of oxidation. Difficult to tell if there is an arcing evidence, but lake of shiny metal is not good.
 
A set of new plugs with solid tips (not screw on) and a set of new wires is a relatively cheap and easy place to start. Double check all of the P-Mag wire connections while you're there.
 
From the pictures I see:
Scorching on cables
Corrosion
Wrong fasteners
etc..

What other sins are lurking in this airframe?

A buyer of a used car wouldn’t accept it if any of these existed, why do airplanes get a pass?!

Someone is going to get hurt, fiscally and/or physically if “we” don’t do a better job here.

Honestly - it’s time to name & shame the person(s) who did the pre-purchase inspection, and then the previous owner(s), operator(s), builder(s).
 
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