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You're pretty much on it
Posted by JEM (more from JEM) on Wed, 17 May 2006 21:09:30
In Reply to: Re: Testing strategy, Ted Kitch, Wed, 17 May 2006 16:39:46
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When we say "TCS" we really ought to be saying "ETS" since it's the electronic throttle system that's really the irritant.
The electrically-operated valve on the firewall switches on and off the vacuum to the ETS vacuum safety system. Normally it should be on, but if the ETS brainbox thinks there's something mismatched between throttle position and pedal-potentiometer position it'll shut it off and vent the ETS vacuum system to atmosphere.
The red-and-white check valve is supposed to prevent positive manifold pressure (turbo boost) from getting to the ETS vacuum system. When the turbo is making boost the ETS vacuum system is isolated by the valve and has to hold whatever vacuum it has.
The whole purpose of all this is that there's a bellows in the throttle body that controls the linkage for the limp-home throttle cable. Under normal operating conditions the vacuum sucks up that bellows and keeps the cable from engaging. No vacuum = cable linkage drops into place = limp-home.
Interesting, isn't it, that the safety system that's supposed to engage in the case of an ETS failure is in fact the cause of most ETS failures?
posted by 198.144.20...
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