New radio showing engine interference

[Timbuick]

Just fitted a new Kenwood CD/radio player using the OEM wiring. When running, there is interference that rises and falls with rpm. Didn't happen with OEM radio, any ideas?
The only wire I didnt utilise is the brown wire that fits along with the orange live feed that plugs inthe back of the oem unit.

 

[TurboBuRick]

Sounds like the head unit has a bad ground. Try relocating it to a different spot.

 

[Timbuick]

OK, I used the OEM wiring for earth. Should i just run a straight earth from anywhere on the head unit to a solid earth?

 

[TurboBuRick]

Yes. Just keep in mind, the shorter the better when grounding stereo equiptment.

GL

 

[Timbuick]

Thanks , will do.

 

[Timbuick]

OK, I ran a short (5") earth from the unit to a new earth and no change. Would i be advised to remove the current OEM factory earth and just run the black earth wire from the unit wiring plug to a solid local earth?

 

[Timbuick]

I think I may have found it

Points 2 & 5 in the link below.

Noise Prevention

will try again later.

 

[Timbuick]

Nope didn't work. Ran a single earth from head unit to chassis, disconnected factory loom earth. No change. Radio still buzzes:frown:

 

[TurboBuRick]

Other causes could be bad spark plug wires or a bad alternator.

Are you running any amps?

 

[Timbuick]

No extras, just a simple head unit exchange from the OEM unit. Plug leads are recent and ohm out well and also 'cured' a misfire I had. Alternator seems fine. I can leave the car two weeks and she fires right up. Shows 13.5v at idle.

I'll check the earth from the battrey next in case it's a touch loose. The noise only occurs with the radio, not when playing CDs.

 

[grocerygetter]

that means its an ignition problem more than likely.

 

[newtownhood]

What kind of plugs and wires are you running? Just because a wire is "good" doesn't mean it's shielded properly. Stock coil pack system? MSD boxes always create horrible engine noise. This might sound silly, but you're running a stock hood, right? Stock 94+ Mustangs with plastic hoods used to get horrible engine noise, so ford put a shielded mat that would actually get hooked to the body for ground. Since your hood is metal, maybe you could try just adding a braided ground wire from the hood to the body? I'm a kenwood dealer and I haven't experienced that issue before in any of the cars I've installed them in. You're just running the headunit without amplifiers, correct?

 

[Turbo Loyd]

Shows 13.5v at idle.

Might want to check out the alternator like TurboBuRick already advised. It should be putting out 14.3 to 14.7 volts at idle after start up. When mine read that low it was typically one of the diodes in the bridge that was bad. This could cause electrical noise. Seems like the diode by the output connector is subject to failure if that connection is slightly corroded or loose.

The diode bridge is easy to replace for less than $50 as a DIY project.

I have a VDO tach in the TR that gives strange readings when one of the diodes is bad, in the alternator.

 

[Timbuick]

Ok guys, thanks for input. The car is running OEM style wires and coilpack. Hood is steel. I'll check the alt connector as I fitted a hotwire recently. I think it may be the alternator. That said, the car charges perfectly and I can start the car after two weeks without use and the battrey is always fresh.
Previously had this Kenwood unit (no amp) in a '69 Mercury Cougar without any interference.

 

[sykegn]

try cutting the ground and let the unit ground through the antenna. i have seen this work before because of a ground loop. you can also try a small coil or cap on the ignition lead and batt lead. btw are you using an external amp?

 

[Turbo Loyd]

That said, the car charges perfectly and I can start the car after two weeks without use and the battrey is always fresh.

The TR when the VDO gages were erratic always seemed OK, but the power windows were not so quick, as when they are running at 14+ volts. One of the three windings in the stator will be very inefficient.

 

[Timbuick]

No external amp.
The power windows are awful. It can take 10 minutes with repeated attempts to get the passenger window up. I need to take a closer look at the alternator readings on my scanmaster.
I'll do a check today and report back.I have ordered a cheap noise suppressor, but i know this is just a band aid.

 

[Timbuick]

OK. all connections tight, radio cannot work with aerial as ground only.
Alt readings are 13.5 - 14.0 with car warmed up.

 

[TurboBuRick]

The alternator can charge fine and still have a noisy output.

As a test, you could take the belt off and run the motor without it. This would tell you beyond a doubt if it's alternator causing the noise.

 

[newtownhood]

the inline noise supressor should help. Just make sure you hook it to the red switched wire and not the yellow. Does the car have a power antenna? If so, make sure the braided ground from it is hooked up in the inner fender or it's not corroded. That will induct noise too. Try connecting a ground wire to the case of the radio and see if it makes any difference too.