[RFI] Diesel "ignition" noise (actually injector solenoids?)

[Morse, Earl (E.A.)]

Rick,

It is a common problem on late model diesels.

With the use of high pressure injectors it takes a 100V pulse to actually fire the injector.  There is also some back EMF from the solenoids as the pulse ends and the solenoid opens.  Unfortunately the diodes to clamp the back EMF are usually located in the Injector Driver Module (IDM) where they protect the IDM from the back EMF transient.  By that time the couple feet of wire connecting the two has radiated the emission.

Place the clamping diodes at the injectors, shield the wires, and round the edges of the pulse that fires the solenoid and the problem should subside.  Not recommended for appliance operators/drivers or vehicles in warranty.

Earl
N8SS

Message: 2
Date: Sun, 20 Jun 2004 19:03:57 -0700
From: "Richard (Rick) Karlquist (N6RK)" <richard at karlquist.com>
Subject: [RFI] Diesel "ignition" noise (actually injector solenoids?)
To: <rfi at contesting.com>
Message-ID: <MGEKKFGEAIKJOOPJPGIKOEEFEEAA.richard at karlquist.com>
Content-Type: text/plain;	charset="iso-8859-1"

I rented a diesel truck over the weekend to move a
tower and noticed that the (apparently factory installed)
Delco AM/FM radio was useless on weak signals due to what
sounded like ignition noise.  The noise went away
if I took my foot of the throttle, leading me to
believe that it was caused by fuel injector solenoids
or something like that.  The noise was bad on both AM and
FM, making me wonder if it was via the 12V supply as
opposed to RF.  Is this a common diesel problem or
just typical GM incompetance.

I used to have a diesel VW and it produced no noise
whatsoever on the HF bands.

Rick N6RK