Re: TFI Ground Question
The ignition coil does not 'HAVE' to be grounded.
If it is grounded, or next to the 'Ground Plane' (Large chunk of metal, like the engine block) it will not do dastardly things to your radio or computer equipment via the transmission of Electro-Magnetic interference (EM Noise).
If the high voltage side of the ignition system has a defect, you will find Radio Frequency interference (RF Noise).
If you flip your radio on, especially on the AM (Amplitude Modulation) band, and you hear your ignition, then you probably have a coil wire, cap, rotor, plug wire or plug problem.
Try a spot of dielectric grease on the rotor nose, and a little touch on each of the cap terminals and see if the noise stops...
If not, get a new cap and rotor WITH BRASS TERMINALS, and try a little dielectric grease on them when you install them.
(Everyone is amazed with that grease on the rotor nose trick!!)
As the ignition fires, it oxidizes the metal in the cap and rotor, and creates resistance.
A little grease helps keep the free arcing to a minimum, and greatly dissipates the noise source.
Connecting a Capacitor to the positive side of the ignition coil will help with ignition noise also.
The two basic types of ignition noise that appear in automotive electronics are easy to understand.
EM noise is the created by the forming and collapsing of the magnetic field inside the ignition coil.
A sheet metal shield (metal beer cans are always stylish!) over the ignition coil will block the EM noise for most sensitive equipment...
RF noise is created when large voltages try to get through a restriction.
Cheap plug wires, bad plugs, corroded or charred cap connections...
The noise created skyrockets when there is an air gap, like a break or loose connection in the coil or spark plug wires...
These are easy to diagnose with a cheap radio/ tape player....
Turn the radio on AM, and find a spot where there is no station.
Rev the engine, and see if you can hear the ignition in the radio.
If you can, then put in a tape with nothing recorded on it, or find a tape with a long silent spot at the end.
Switch over to the tape player, and see if you can still hear the ignition in the speakers.
If you can hear the ignition in the radio, and not the tape player, then the noise is RF or EM, and can usually be traced back to the ignition or the alternator.
If you can hear the 'ignition' while the tape player is on, then it's not RF or EM at all.
It's probably power interruption noise from something like an ignition module, ignition coil, or alternator. (Heavy Power Switching Noise, not high voltage noise)
It's not your Plug wires or distributor cap.
High voltage switching noise by taking your radio off the same line as the component making the noise...
And by using a capacitor on the power side of both components.
"I Have The Body Of A God... Buddha"