View Single Post
flightlead404 flightlead404 is offline
Registered User
Join Date: May 2015
Posts: 798
The vacuum solenoid-valve (37 in the diagram, aka Change Over Valve aka thermo time switch) is plumbed thusly:
-Nipple underneath the electrical connector to the throttle body
-Nipple opposite the electrical connector vents to atmosphere
-Nipple on top at 90 degrees to the distributor

Blue RHS line on the distro pot is the Retard Line, and goes to the vacuum solenoid Thermo Time Switch (TTS)/change over valve mounted on the LHS of the BOV housing, and thence to the front port on the throttle body which is ABOVE the butterfly valve. This one has vacuum on it at idle. When the engine is at temperature, boost pressure retards the timing to avoid detonation. The TTS disables vacuum retard during warm up which raises idle speed and is part of the cold start routine that lasts about a minute.

I've read this many times btw, and it makes me realize this emissions control/cold start aid is potentially dangerous as it prevents ignition retard on boost when the engine is not up to temp. Admittedly, you'd probably have to hit boost leaving your driveway as it come up to temp real quick but still....
Old 09-15-2017, 06:36 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)