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Re: [ST] RS post-idle report



Barry

Sounds right except that the ECU doesn't touch the throttle butterflies
which is what the idle stepper thingy does instead.  It does measure
their position, but only you (via twist grip) and your mechanic (via
screw-stops) adjust/move them.

Um..  Taunton...  a bit far but I'll bear it in mind for retirement
<G>

Chris Harwood
00 RS

>>> barrycroft@xxxxxxxxxxx 12/10/2005 11:27:15 >>>

I'm glad Marc asked what a stepper motor was. Cos I didn't know either,
so I went and looked it up! It's an electric motor with a cunning
arrangement of magnets so it can rotate a fixed number of degrees then
stop, in a series of steps. They're used in home printers and fax
machines and stuff to control the paper precisely, but also commonly
used in fuelling systems, in the Triumph's case to control the air flow
by controlling how far open a bypass is. When the throttle is closed it
moves a tiny plunger in discrete steps to control the idle. I haven't
actually found precise details of Triumph's system, but on other
vehicles I've seen steppers move in anything up to 200 steps from fully
closed to fully open. And two things can go wrong mechanically: the O
rings sealing the plunger can leak (so air is passing even when closed),
or the plunger can get dirty and stick partly open. I think my problem
was the latter, since the symptoms were right - when the plunger sticks,
the ECU 
 *thinks*
 that it's fully closed even when it isn't, and tries (but fails) to
compensate by changing the number of steps open it tells the plunger to
be at, but also meanwhile adjusts the throttle butterflies, mixture,
timing etc. According to my job sheet the mechanic put in new seals AND
cleaned the plunger, so I can't tell which it was - but I can at least
tell that the mechanic knew what he was doing. That was Taylors in
Taunton for anyone local, a good shop.

 

Barry

2000 RS

		
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