CAPICATORS FOR 308

If its that bad I would suspect poor or non existent ground connection on the antenna and/or open circuit antenna connection. This might account for why you've had it with both old and new radios fitted. Check these and the ground connection of the unit to the chassis before doing anything else. Also check the bonding connection from the block to the vehicle chassis.

Is the noise rev related? Is it a whine (alternator) or pulses (ignition)?

Do you get the noise on the radio reception only or (assuming you have it) when you play a CD etc?

I have a glass fibre bodied 308GTB and, with the antenna up, I get great noise free reception on 200kHz and 500 - 1200 kHz, no problem. Noisy as hell and no signal with the antenna down though!

 

I'm not sure where the engine block to chassis ground is but look for a thick starter type cable somewhere between the engine/ transmission and the cghassis. Chances are this is not the problem if the car cranks ok as it carries the starter motor current in most vehicles.

I assume we're talking about a steel bodied car with original distributor/coil ignition and FM radio with antenna on the rear right hand wing.

I still think the most likely cause is a poor ground at the base of the antenna. If you can get to it, you could try tightening or wiggling (that's a technical term) the base with everything running and see if the noise changes, gets worse or goes away. If the base clamp and/or the body is locally rusty all you can do is take out the antenna and clean up the clamp and body metal where the clamp is supposed to make contact.

If you have a multimeter, before you take it apart you could try disconnecting the antenna from the back of the radio and check the resistance from the outer of the antenna plug to where the radio is grounded to the chassis. It should be zero Ohms or very close i.e. no more than a couple of Ohms. Also check the resistance between the inner and outer connections on the same connector. This should be open circuit (infinity). Lastly you can measure the resistance from the antenna rod to the inner of the cable at the radio end. This should be zero Ohms (short circuit). If any of these tests give the wrong result you have either a faulty cable or ground connection somewhere.

Another good candidate is the spark plug in-line suppresser resistors (plug extenders) which are either black or red and sit under the rubber bungs on the plugs. These can go high, low, open, short or intermittent with age and could be the source of the problem. In the UK they're about £6 ($10) each and will also screw up the engine performance if they're faulty, causing misfiring, particularly on load. Again, check them with your multimeter. I believe if they're black they should be zero Ohms, or thereabouts and about 1.5k to 2k Ohms if they're the red ones. I'm not absolutely sure which way around this should be so hopefully someone will pop up and correct me if I'm wrong on this point, or check the archives. Either way, a good check is to see that they're all about the same. If they're over about 2k Ohms, chuck them away! While you're at it check the plug gaps if they've not been done recently.

If all of these tests buzz out ok you'll need to identify the source of the noise and to detirmine whether its a clicking or whining. Both will change in frequency and probably intensity with revs if its engine electrics causing the problem.

The last possibility is that there are a number of suppresser capacitors (your original question!) on the alternator 2.2uF, on each coil (I have two coils on mine) 0.5uF and on the fuel pump, also 0.5uF. If the noise starts as soon as you turn on the ignition and before you crank the engine the pump suppresser is a good candidate. This would also be more constant with engine revs.

Good luck.
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