car radio problem

[Lindsey Wolfer]

I have Motorola cp200 radios in my Van Diemen Fc zetec. Transmission from car (driver) to crew is clear when engine off, but engine on produces static-whine. Crew to driver is loud and clear. The voice is clear but as the engine revs the whine gets louder and higher pitch; almost like alternator whine. I had wiring harness, radio and antennae wire checked by Racing Electronics and its all ok. The only thing not checked are the helmet mic which they said is mil spec and rarely goes bad, and the PTT switch which is 8-10 years old. I tried another switch , also older-david clark- but same results. I don't think its the PTT switch ? unless the coiled wire has shielding break? It sounds like engine noise but the radio system uses shieded cable so it shouldn't be a problem? I have used this system for a few years , now, but didn't have the problem before.
Anyone have any ideas or similar problem?

[Rick Kean]

May be too many to list here, but it's a good way to prioritze the diagnostics.

Rick

[ghickman]

I'd check the following in this order:

Plug wires
Coil wires
Plugs

I don't know much about the Zetec powered FC but isn't the alternator driven by the axle? Do you get the static increase while the car is sitting motionless and while revs raised?

[Lindsey Wolfer]

yes, the alternator is on the rear axle. I get the whine increase just reving the engine while motionless.
I put a new coil pack and new wires last year; but they are replacement type by MSD, not Ford part
If the radio wiring harness are all shieded doesn't that prevent coil/plug/sp plug wire noise?

[ghickman]

Did this problem just come up our did you have it prior to the plug / coil wire change?

I'm a pilot and my experience with radio wire sheilding doesn't make them not prone to ignition noise.

If I had to guess it sure sounds like ignition noise. Check your coil and make sure it isn't cracked. Are you using resistor type plugs?

[Lindsey Wolfer]

Problem seems to be fixed. Racing Electronics experts recommended I install a ground wire between the engine and chassis. Its about 85% better.
Thanks to those who offered some help and to Racing Electronics.