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

To: "Morse, Earl (E.A.)" <emorse@ford.com>, <rfi@contesting.com>
Subject: Re: [RFI] Diesel "ignition" noise (actually injector solenoids?)
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Mon, 21 Jun 2004 13:02:25 -0400
List-post: <mailto:rfi@contesting.com>
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.>>>

In my 95 7.3L Power Stroke, the back pulse significantly
exceeded 1000 volts. That's more than "some" backpulse, hi
hi.

<<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.>>

The shields inside the Ford Diesel cables were grounded only
at one end. I grounded them at the solenoid ends to valve
cover bolts, and did other grounding to the vehicle. I was
always afraid to clamp the injector solenoids because any
back-pulse clamping would slow release times significantly.
As far as I could tell, NOTHING clamped the solenoids.

My brand new PSD appears to have the same problem.

73 Tom


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