Visual Check (Fuel Leak)
- Remove air cleaner assembly and check for any visibly obvious signs of fuel leaks around engine. For V8 engines, remove fuel pump relay (under hood near fuse panel). Bridge fuel pump relay connector pin sockets No. 7 and No. 8 with jumper wire to establish fuel pressure.
- For 4 and 6-cylinder engines, remove MAS unit from underhood component compartment area, near CIS-E control unit. To remove MAS unit, turn top knob from position No. 1 to position No. 0 and lift/pull MAS unit out of electrical socket connector. Using fused jumper wire, jumper pin socket No. 2 with battery voltage source to establish fuel pressure.
- Remove air intake duct or air cleaner assembly from airflow sensor and push sensor plate down manually. After slight amount of free travel, a uniform resistance should be felt throughout sensor plate travel. No binding should be felt when sensor plate is released. If returning upward movement of sensor plate is slow, feel for resistance of fuel distributor control piston returning against sensor plate lever arm. No binding should be felt, otherwise replace airflow sensor/fuel distributor assembly.
- Push airflow sensor plate completely down and briefly hold. No fuel should leak past control piston on underside of fuel distributor. Very slight fuel see page is acceptable for control piston lubrication purposes. If no obvious fuel leaks are found, go to next test.
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.