[RFI] Spark plug noise

Eric Gustafson Eric Gustafson <n7cl@mmsi.com>
Fri, 7 Jul 2000 13:46:50 -0700

Hi Kelly,

You could always replan your trips so that they don't require
right turns ;-).

Actually, I have had this happen in a number of older cars.  The
cause was not the same in each case.  The four main things to
check are (not in order of probability):

1.  Good bonding between the radio case ground and the vehicle
    frame local to the radio.  Note this is not the same path as
    power ground in most cases.  This should be an actual short
    braid strap.

2.  Proper bonding strap connections between the engine block and
    vehicle frame and firewall.  You might want to check your
    motor and tranny mounts while you're at it.  They might be
    permitting too much travel.  But you'd likely have a forward
    vs reverse component to the problem if this was the cause.

3.  Proper bonding between firewall and fenderwell sheet metal

4.  Secure ground connection for the antenna feedline to the
    vehicle body at the antenna.  This includes antenna feedline
    shield integrity from the radio to the body sheet metal.  If
    this is the cause, and it is due to a loose antenna mount to
    the sheet metal, you can duplicate the problem sitting still
    at idle by gently forcing the antenna to the left or right.

The last one being the most likely cause, IMHO.

73,  Eric  N7CL

>Date: Fri, 07 Jul 2000 14:51:45 -0500
>From: kboswell@aetn.org (Kelly Boswell)
>Anybody heard of one like this;
>My 90 Nissan pick-up has spark-plug noise on the AM radio, but
>*ONLY* when turning right.
>1.) The sound is like your typical spark-plug noise.
>2.) Using a turn signal makes it worse.  Also, it doesn't take
>    much of turn for it to occur.  Merely enough right turn to
>    exit from an interstate will suffice. 
>3.) None of this happens when turning to the left.
>Thoughts, suggestions?
>Kelly, ka5mgl

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