Removing Emissions Vacuum

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When disabling the EGR (exhaust gas recirculation) and ARV (air recirculation valve) on the W123, vacuum components related to emissions operation can also be removed. This has the advantage of significantly enhancing vacuum operation by eliminating leak sources and cleans the engine compartment. This guide is specifically written for all 1985 model year (Federal and California 617.95x motors) 300D and 300SD vehicles. Note that this guide is strictly for vacuum troubleshooting, and should not be construed as advice for long-term removal of emission equipment.

Project Box
Part Number(s):
Part Cost: $4
Best Place to buy: Typical places
Cost to Have it done in a shop: $
Difficulty Level: 1
Frequency: As needed
Tools needed: None
Special tools needed: None

Vacuum Diagram

This diagram provides a useful start to understanding the necessary procedure.

1985 617 VacuumDiagram FED CalElimi.jpg

Original setup

This image shows the original vacuum tubing:

  • A: These are the vent out lines from the pressure converter. These connect to an air filter, which will then go through the firewall.
  • B: This is a white/blue vacuum line from the switch over valve going to a four way connector. That four way also has a line from the vacuum transducer, a line from the main vacuum pump, and a line to another four way (holding yellow dashpot, green vacuum line, and brown vacuum line).
  • C: This is a white/brown line from the EGR going to a three way connector. One connection on the three way goes to the main vacuum pump and the other goes to a small three way, one branch which goes to the transmission dashpot.



The following steps outline the process necessary. All items in bold are new parts you will need.

  1. Disconnect the white/brown line from the three way connector.
    1. Cut a piece of vacuum hose to approximately 4 inches.
    2. Connect the main vacuum line to the line going to the small three way connector using a 4inch vacuum hose
  2. Disconnect the white/blue line from the four way connector.
    1. Disconnect all remaining connections and remove the four way connector.
    2. Hook up all vacuum lines, except of course the white/blue, to a new three way connector
  3. Disconnect the vent lines from the air filter
    1. Since these are outgoing lines, it is not necessary to cap them.
  4. Disconnect the electrical connection from the pressure converter
  5. Disconnect the electrical connection from the switchover valve

The image below shows the new connections in place, and you can still see the two disconnected vacuum lines in the foreground.