Notes

Before attempting to diagnosis a fuel system problem technicians should review the section concerning COMPUTERIZED ENGINE CONTROLS. There, the technician will gain an understanding of system operation and diagnostic methods. Fault code information contained therein will guide the technician to recognized problems eliminating wasted time and frustration.
Refer to the FLOW OF DIAGNOSIS, CHECKING THE BASICS, SYMBOLS and TOOLS sections for information concerning necessary tools, testing symbols, and an overall diagnostic approach for each problem.

COMPONENT TESTING gives detailed test procedures for individual components.

The COLD START TEST covers information concerning "cold" CIS-E system pressures and operation.

The FUEL PRESSURE AND DELIVERY VOLUME TEST covers information concerning fuel pumps pressure and CIS-E fuel delivery volume.

The FUEL SYSTEM PRESURE AND INTERNAL LEAKAGE TEST provides information concerning the condition of the fuel distributor, correct operation of the electro-hydraulic actuator, fuel pressure regulator, fuel pump check valve, and fuel accumulator.

The FUEL QUANTITY COMPARISON TEST checks the ability of the fuel distributor to provide uniform fuel volume to each fuel injector.

The DIAGNOSIS BY SYMPTOM provides a list of possible causes for various problems that may be experienced.

Testing Schematic:

TEST CONNECTION EXAMPLE

In this example the Mercedes Benz Socket Box is being used to run a voltage test on the CIS-E system. "N3" in the upper section of the box refers to the CIS-E control unit; the symbol in the middle of the box refers to the Mercedes Benz Socket Box; the voltage symbol at the bottom of the box refers to the connection between socket "5" and "14" of the socket box.

NOTE: If the Mercedes Benz Socket Box is not available carefully backprobe control unit harness connectors. Refer to CHASSIS AND ELECTRICAL DIAGRAMS for specific electrical diagrams.