> Perhaps something freewheeling for the hydraulics
> or something?
>
> Just wondering as I am always curious! :-)
The noise in modern diesels is almost always the injector
solenoids. All of the systems I've seen turns each injector
on at the appropriate times (near the top of the compression
stroke). The injector control in my Ford products controls
engine oil pressure that drives a shuttle. The other side of
the shuttle has the fuel. The engine oil pressure pushes the
shuttle to inject the fuel.
Since the system has to have precise and pretty short
control times. A V8 4 cycle engine might turn nearly 3000
RPM, and that would be two crank revolutions for each power
stroke. Each injector has a maximum of 25 very short
precisely timed pulses per second.
Since the open time is so very short the manufacturer cannot
suffer with back-pulse suppression. The result is the open
circuit voltages are very high, and have sharp spikes.
Now there are certainly other things, like fuel pumps, that
make noise. My Ford trucks and a friend's Audi have exactly
the same problems.
http://www.w8ji.com/rf_noise_powerstroke_diesel.htm
73 Tom
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