I get radio interference when the ignition wire is connected to the sparkplug, and when I unplug the spark plug wire from the spark plug it goes away. What do you think would cause this since the ground is supposed to be in the spark plug wire?

Don't want to sound like a smart ***** but yes the interference would go away with the plug lead disconnected. The engine wouldn't run .... therefore, no interference.

Seriously though, this sounds like a common problem. Are you sure you are pushing the plug lead far enough onto the plug? If you are using the common Rcexl ignition or something similar that uses a metal plug cap, all of the hex part of the plug should be covered when the cap is pushed on far enough.

Everytime the magnet passes the hall sensor I get a glitch on the plane. The elevator and rudder twitches. But when I unplug the plug wire and turn the engine over and the magnet passes the sensor it doesn't glitch. Could the metal on the metal shroud of the plug wire touch the fins on the head and cause interference? thanks

The metal shield of the spark plug cap touching the fins of the head would have no effect on the interference.

Maybe the post below had something to do with the problem.<hr />BEWARE! I just found out that you should not connect your engine kill switch to the power lead on the ignition, but it should be connected to the hall sensor lead from the ignition. I tried connecting to the power lead and all the wiring got red hot in a few seconds, fortunately I unhooked the battery in time before it all melted down.

If the braided metal of the sparkplug wire touches the fins, it will wear a hole in the shielding braid and you may get interference.

The cap/ braiding must be grounded to the engine or you will get interference. That's the ground for the module. A buddy took the ring off the cap where it's an interference fit on the base of the plug and got all kind of glitches. I soldered a wire to the braid and grounded it to the motor. No more interference. Just for a test, put an aligator clip jumper wire from the braid to the motor and see what you get.

If the plug cap is pushed all the way onto the plug, it HAS to make good electrical contact. This also completes the return path for the spark voltage to ground. The whole system is shielded and there should be very little RF energy escaping to cause radio interference. There should also be NO NEED for any additional ground connections. Just that simple.

Protect the shielding on the plug lead with spiral wrap or split lomb or something similar. But protect it at all cost from damage. If it rubs on anything it will wear through in short order causing damage to the plug lead.

Looking at gas engines at the swap meets, The braiding on the sparkplug wire most often has a damaged place on it that could leak RF.

As I said, the guy took the wire ring off the bottom of the plug cap so their was no longer a good ground. the bottom of the plug cap just flopped around on the plug. causing an arc. That's where the interference comes from. The added on wire serves the same purpose. It grounds the shielded wire.

Damaged wire is tolerable. It's the fact that it's not grounded where the problem lies.

Why wasn't it grounded, if it's making good contact with the metal spark plug cap shell it's grounded.

For the third time, there was no wire ring on the bottom of the plug cap to hold it tight to the plug. The guy took the ring off and flung it. Its purpose is to get a good ground. Motors like the Quadras use a carbon plug wire and a resistor plug to stop interference but you"ll notice they have to have a wire to ground the ign. module to the motor. The braided wire and metal plug cap serve as ground for the module, as long as the cap is on tight and has the ring to secure it to the plug base.

I would have just put a small hose clamp on the plug cap.

Yep, seen that done before too and works well.

I use tiewraps. This keeps the shells together. I do need some leverage to get the caps off, but they stay tightly put.

I had the same problem with aileron servos, but only noticed it when the engine was running. Ended up redesigning the way I had the electronics set up in the plane. moved all RX , servo wiring as far away as possible from engine electronics. problem solved