Ignition RFI

[W3MPS]

Ok guys, here's a question for all of you. I've had a CB in my '92 Jeep Cherokee since 2009. No funny stuff, just a plain ol' CB. And I had no tx induced problems problems at all.

I put a new engine in in the summer of 2010. Now I am having all sorts of problems with the radio making the ignition go nuts when I try transmitting. And by nuts, I mean miss fires, popping, backfiring, and general bad juju for the motor.

So far, I have cleaned up all the chassis ground points, made sure nothing had been touching that shouldn't be, and bonded everything. The only thing that really changed was I had to splice on a new connector for the pick up coil for the distributor, and that part of the harness ended up being about 6 or so inches longer.

Where should I start troubleshooting at? Cleaning up the grounds decreased the severity of the problem, but did not eliminate them.

[N9FE]

For grins try putting some tin foil around the new splice by the distributor. Wierd a low wattage CB would do that though.

[W3MPS]

Who knows, maybe the splice made it near resonant on or around some harmonic or whatnot. That's my current theory, it's on tomorrow's to do list.

[N8YX]

Undo the splice and put a few slip-on ferrite beads along the conductors, then redo the connection. Use beads with an Ft of 20MHz or lower as a start. Then add a couple clamp-on (split) ferrite cores of the same mix to the main ECU harness.

[PA5COR]

Large enough clip on ferrites will clip over the cable without having to redo the splice.
Put a few next to eachother to amplify the rf choking.
Get your + and - Cables directly from the battery, ( fuses in BOTH) and also get some ferrite over those.

That should sort it, put some ferrite next to the transciever too, some rf might leak into the wiring in the car and reach the computer.
Find computer, check ground connections, and add ferrite there too.

Glad my van has only a stupid driver as computer ;)

[W3MPS]

Thanks guys. It looks like I have a nice project on my hands for next week. (Ahh, the fun of having to work weekends)

I had already done a direct run to the positive post with an auxiliary power bus, guess now I'll finally get around to running the ground bus to match.

And of course, I should know better. Adding or subtracting wire length is a great way to make things RF sensitive that you don't want to be.

[N5RLR]

Try a "twisted pair" of wires from the rig to the battery; offers some self-shielding properties.

[W1GUH]

'FE said...

Wierd a low wattage CB would do that though.

He's not talkin' about how many pills he's usin'. Just sayin' ;)

[W3MPS]

He's not talkin' about how many pills he's usin'. Just sayin' ;)

Nope, no Illudium Q-36 Explosive Space Modulator is in use.

[W1GUH]

Forty-roger on that, good buddy. Keep it between the ditches, y'hear?