breedon@ucdhep.ucdavis.edu writes:
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>With the latest discussion regarding the benefits, moral and otherwise, of
a
>properly operating EGR valve, I thought I would interject a question I
have
>posted before and never received a satisfactory answer: What is the
purpose of
>the vacuum hose connection off the EGR valve which leads to what appears
to be
>a small connector or switch associated with the choke linkage at the base
>of the rear carb on a '74 TR6 engine? This flows through one port of a
>Y connector to the top of the EGR valve; the other port of the Y leads to
a
>fuel trap then to a connection at the top of the same carb.
>My guess is that the lower connection is meant to disable the vacuum draw
from
>the upper connection to the EGR valve when the choke is pulled. Or am I
>mistaken and this is how the throttle linkage reduces the effect of the
>EGR valve at full throttle (and it just happens to be next to the choke
>mechanism)?
Yup. This valve dumps the vacuum to disable the EGR valve when the
choke knob is full out - something you rarely do in Cal ;-).
>I am asking because in my drawn-out attempt to pass CA smog, during the
last
>pre-test I took (and failed) the mechanic said was EGR valve was not
>operating. The vacuum connection to the choke (and/or throttle) mechanism
>at the time was not secure, having been faultily replaced by a previous
>smog mechanic. I am hoping that this was the cause of my problem and that
>the valve itself if OK.
If I were you I would eliminate all that and connect the EGR line directly
to the carb port. Living in California you probably use the choke
sparingly if at all and this additional control is academic. Those of
us in the snow belt don't have that luxury.
>BTW, how does one tell if one's EGR valve is working?
If you reach up underneath the diaphragm housing, between the spokes, you
can
feel the underside of the diaphragm. Start you engine. At idle there is
no vacuum on the diaphragm and the valve is closed. Rev the engine and you
should be able to feel the diaphragm raise about 0.1 inches. Mine does.
>Thank you in advance for any advice, Richard
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The operation of the EGR is pretty straight forward. Vacuum is used
to open the valve. The more vacuum (caused by a throttle that is more
closed) the more it opens. At idle this would cause a problem so the
vacuum source is a special port that only provides vacuum when the
throttle is open.
Good luck on passing emissions testing.
Dave
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