XR4Ti Archived Tech Articles

    What is Trailer Hitching? - A contribution by Dr. Keith Delahoussaye that sums up trailer hitching, the problems it can cause and why, and what you can do to solve it.

Post Date:    Tue, 23 Oct 2001
Subject:      Re: Bypass Valve and vacuum leak fixed!
List:         imon@lists.merkurowners.org

>Please define "trailer hitching"!

Ever tow a really heavy load on a trailer, and lift the pedal while driving
a steady state??  The trailer alternately pushes and pulls back on the
hitch, jerking the tow car around.  With a loose load, and some wear on the
hitch, it can REALLY make things interesting . . .

Lifting the throttle on a turbocharged vehicle at decent RPM and boost can
create a similar effect.  Snapping the throttle shut forms a pressure wave
that can rebound off the throttle plate so hard, it will lift it open
slightly, relieving the pressure, letting them drop, and so on.  Also, that
reversion wave smashes in to the impeller wheel, sometimes with enough force
to bend the vanes, and has been found to bend the throttle plate.

Longer charge air paths, like air/air front-mount intercoolers, seem to make
trailer hitching worse.  The BOV/BV's stops this by opening when vacuum is
sensed behind the throttle body.  This relieves the pressure (to atmosphere
in a blow-off valve, and back into the pre-turbo air system on a bypass
valve), allowing the turbo to remain spinning at speed.   Instant boost on
the reapplication of the throttle.  No damage or wear to the turbo.

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Published by Chris Anglin.