Engine Surging at Partial Load
07.1T91091 Engine Surging at Partial Load Engine 602.962 9/91Cause:
Engine surge is caused by erratic boost pressure changes, created by fluctuating vacuum signal to boost control valve vacuum actuator or waste gate control vacuum actuator.
Remedy:
^ Check that injection pump rack position sensor plug connector (L7) is tightly fastened.
^ Test Engine Overload Protection system.
^ Check adjustment of boost control valve vacuum actuator (S.I. MBNA 07.1/17a, May '91, page 2). If the previous test and adjustment measures have not corrected the condition, continue with the following test steps:
1. Using a Y-connector, connect a vacuum/pressure gauge to the intake air pressure line from the intake manifold to the intake air pressure sensor (B5/1).
2. Drive vehicle under partial load (boost control valve actuated).
3. The reading on the vacuum/pressure gauge should drop between 0 mbar (ambient pressure) and approx. 150 mbar vacuum.
4. Observe vacuum gauge needle. It should move according to load change only.
5. Oscillation of the needle with the engine at partial load indicates a faulty vacuum transducer (Y31/2) for the boost control valve vacuum actuator or vacuum transducer for the waste gate control (Y31/3), either of which will cause engine surging under certain conditions.
6. Using a Y-connector, connect vacuum/pressure gauge to the vacuum line between vacuum transducer Y31/2) and the boost control valve vacuum actuator. Violent oscillation of the needle between 0 and 100 - 300 mbar with the engine at partial load indicates a faulty vacuum transducer Y31/2).
If test is negative and step 7.
7. Using a Y-connector, connect vacuum/pressure gauge to the vacuum line between vacuum transducer (Y31/3) and the waste gate control vacuum actuator on the turbocharger. Violent oscillation of the needle between 0 and 100 - 300 mbar with the engine at partial load indicates a faulty vacuum transducer (Y31/3).