Ignition Noise

I need some help with an odd issue. I am getting ignition RFI, not on my com radio(it is quiet), but on my transponder. The ignition noise can be seen in the form of constant replies from my transponder(light never goes off when engine is running). It does not seem to be an issue for ATC - they never complain(long XC under Flight Following), but it does basically render my Trafficscope worthless. When the transponder constantly replies, the TS reports a target at 0.5 miles and same alt, constantly.

My Setup
O320 dual EI auto plugs BR8ES
MSD ignition wires
TDR-950 Transponder
Trafficscope VRX

This is the second time I have seen this. The first time, I replaced the ignition wires and the problem went away. Now 100 hrs later I am seeing the same thing. I did try moving the antenna back further on the fuse to no avail.

I was told replacing the plugs might solve it as the resistors might have gone bad. I'll risk the $12.59 to replace the plugs. Replacing the wires is a bit more $$ and a bigger hassle.

Any other thoughts? What might cause the wires to fail(leak RFI)? Is a notch filter available for transponders? Is reply sensitivity adjustable on transponders? My engine runs fine, com radio sounds great.........

Thanks in Advance -

Pete, check the hi-tension wire terminals at the spark plugs. I am running dual P-Mags and have noticed that when a spark plug wire is not firmly clipped to the ferrule on the plug or if the ferrule is not fully tight on the end of the plug ignition noise will result. You may have to squeeze the clip on the end of the wire to get it to seat with clamping pressure on the plug ferrule. Any looseness in these connections will cause some arching wich will create electrical noise. With all the connections tight, I get no noise at all.

Martin Sutter
building and flying RV,s since 1988

Noise

Have you tried switching brands? On our Rotax (912S) we did away with the NGKs are replaced them with Auto Lites. Noise was an issue, and still is, but reduced. The plugs were changed due to poor performance (fouled easily and would not recover) Lasted only 35 hrs The Auto Lites have more than 400 and still going. Noise has not disappeared, but still noticeably quieter than the NGKs. Your number should be interchanged with a 4063. It is a resistor plug, and various versions of same heat range.
Though noise was not an issue with our Arrow, the Auto Lites, did last longer and engine performance is more consistant. Bosch is another alternative.
TT
RV10

Thanks

I will look into both of these options and report back