Date: Mon, 9 Oct 95 15:56:55 PDT
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Dave Kautz <dkautz@hpsidms1.sid.hp.com>
Subject: Missing from Bentley
This message is likely to be of interest only to folks owning mid-70s
breadloaves or to techno-geeks who have their emission equipment still
hooked up...the rest of you can prevent the onset of nausea by pressing
the delete key now.
As those of you who read EVERY SINGLE POST may remember that the guilt
of environmental destruction was weighing heavily on me a week or two
ago resulting in the awakening from hibernation of my EGR valve. As I
mentioned at the time, this resulted in a mid-range stumble that was
particularly annoying when the engine was cold.
I found myself mumbling that there is no way that the engineers at VW
would have shipped something that ran like this and that there must
be something wrong. The other evening I gathered my stack of service
manuals and read everything I could find on the EGR system.
In one of the diagrams in Haynes, which has some errors otherwise, I
found a reference to an extra vacuum line used on California spec.
carbureted engines which have a two stage EGR valve instead of the
"plain jane" model used in the other 49 states. Bentley, and I re-read
it carefully, makes NO mention of this.
Now I have always wondered why I had an extra tube sticking out of the
right hand carb and it suddenly became clear to me how this thing was
supposed to be plumbed up.
So here's how it goes, if you've got the same setup: The vacuum line from
the brake booster circuit goes to the single fitting on the right hand
side of the EGR solenoid control valve. The "extra" vacuum advance tube on
the right hand carburetor gets connected to the lower tube on the left side
of the EGR solenoid. The upper tube on the left side of the EGR solenoid
goes to the EGR valve.
I think it's okay to use the vacuum advance port on the left hand carb
for the EGR <it's a lot closer> and the one on the right for the distributor
if you want - I tried it both ways and it seemed to work the same.
And yes, this does get rid of the stumble. I suspect that the stumble was
caused by the abrupt change in manifold vacuum when the EGR was suddenly
fully opened to it's second stage position by the microswitch on the
throttle linkage. With it plumbed correctly it is opened slightly,
to the first stage, by the vacuum from the throttle plate
resulting in a smoother transition to second stage when triggered by
the microswitch.
I realize that this all sounds very complicated and confusing. If anyone
would like more clarification, send me some email at dkautz@hpsidms1.sid.
hp.com and I'll try for a better explanation or a diagram.
Regards,
Dave