Turbo System Test
- Connect vacuum gauge into vacuum line (white/purple/brown) between EGR valve and full-throttle switch-over valve. At idle, no vacuum should be present. Move throttle linkage until play in telescoping rod is eliminated. Vacuum should read 11.8-14.8 in. Hg.
- If vacuum is not correct, connect vacuum gauge between thermo/vacuum valve and idle switch-over valve. Vacuum reading should be 11.8-14.8 in. Hg at idle. Clamp vacuum line on thermo/vacuum valve side. Vacuum level should hold for at least 2 minutes. If not, replace idle switch-over valve.
- If vacuum remains constant, remove clamp and disconnect hose between the 2 switching valves. Actuate throttle linkage until idle switch-over valve is operated. Vacuum should drop. If not, replace idle switch-over valve.
- Reconnect hose between switch-over valves. Disconnect vacuum line (white/purple/brown) from idle switch-over valve, and disconnect vacuum line (white) from full-throttle switch-over valve. Connect a vacuum gauge between white/purple/brown line and full-throttle switch-over valve.
- Vacuum should read 11.8-14.8 in. Hg. Clamp vacuum line and check that valve holds vacuum for at least 2 minutes. If not, replace valve. If it holds vacuum, remove clamp and actuate valve with screw-driver tip. Vacuum reading should drop to zero.
- Reconnect all hoses. Actuate throttle linkage until idle switch-over valve is operated, then disconnect and reconnect vacuum line at EGR valve. If valve does not operate audibly, replace it.
- Connect vacuum gauge between EGR valve and full-throttle switch-over valve. Using throttle linkage, raise engine speed to 1000 RPM. Vacuum reading must be 9.5-10.3 in. Hg. If vacuum reading is incorrect, exchange orifice sizes to correct. If level cannot be obtained, replace vacuum modulating valve.
Courtesy of MERCEDES-BENZ USA