Checking the Basics

All Troubleshooting must begin by "Checking the Basics". Before attempting to diagnose or repair what might be wrong, the troubleshooting technician should look for obvious problems first.

Prior to any teardown, repair or component replacement, the following steps should always be considered.

COMPLAINT VERIFICATION
Whenever possible the repairing technician should personally verify the complaint. Having experienced the malfunction, the technician is less likely to try to repair non-existent faults.

MALFUNCTION VERIFICATION
Today's sophisticated automotive systems are easily misunderstood, which can lead to repairs that attempt to force a particular system to perform in a way that it was never intended to operate. Therefore, the troubleshooting technician should compare the system operation to the nominal system operation as described in the section Description and Operation. Furthermore, the technician is also encouraged to compare the problem vehicle system operation with a known good vehicle.

DIAGNOSTIC TROUBLE CODES
All Diagnostic Trouble Code (DTC) memories should be read and malfunctions corrected. Refer to Computers and Control Systems for trouble code retrieval. Testing and Inspection

PREVIOUS REPAIRS/MODIFICATIONS
The vehicle repair history can provide explanations to unusual complaints which seem to elude normal troubleshooting attempts. Incorrect components, unapproved repairs or modifications can have subtle influences on seemingly unrelated systems.

NOTE - Vehicles with a history of accident damage and repair may exhibit very unusual symptoms.

BATTERY STATE OF CHARGE
Batteries in a state of partial discharge can have a dramatic effect on DME control units and related components.

POSITIVE BATTERY CABLE INTEGRITY
All B+ connections must be in perfect condition for trouble-free electronic system operation. Refer to Electronic Diagrams for B+ interconnects.

FUSIBLE LINK INTEGRITY
Fusible links are employed to prevent possible damage to electrical components and wiring harnesses. These links and their connections must be without dynamic resistance. Dynamic resistance can only be checked using the voltage drop method of testing.

NEGATIVE GROUND CONNECTIONS
As all electrical circuits are a circle, all B- connections must also be checked and verified to be in perfect condition. A poor "common" ground point will cause seemingly unrelated systems to influence one another. High current systems which encounter a poor "common" ground can back feed through other electrical systems causing unusual operation and perhaps inexplicable component failure. As with the B+ side of the electrical system, the ground side should be checked dynamically using the voltage drop technique.

POWER TRAIN CABLE ATTACHMENTS
Metal cables attached to the engine or transmission which appear overheated and/or discolored indicate the need to thoroughly test all ground connections.

POWER SUPPLY RELAYS
Fuel pump and DME main relays as well as their plug connections can be a source of intermittent operation which will not set a fault in the DME fault memory.

CRANKSHAFT AND CAMSHAFT POSITION SENSOR
Monolithic sensors should be checked statically and dynamically. Physical mounting and condition of the sensor and segment wheel must be assured.

HIGH TENSION COIL AND SECONDARY COMPONENTS WIRING
The secondary ignition system should be checked visibly as well as with a suitable engine analyzer and scope. All components should be examined for tight connections and freedom from carbon tracking, moisture and corrosion.

FUEL DELIVERY/PRESSURE
Fuel delivery must begin at once when cranking and the pressure in the fuel system must be within specifications. Fuel pressure retention must be maintained between the fuel pump outlet and the pressure regulator after engine shutdown.

GENERAL ENGINE CONDITION
Verify that the engine meets minimum mechanical requirements. Low compression, vacuum leaks, worn valve train, restricted exhaust etc. must be corrected.

VALVE CLEARANCE AND SPARK PLUGS
These two service items, if out of specification, can significantly impair engine performance. Valve clearance adjustment procedures should be strictly observed. Spark plug type, condition and gap must verified according to specification.

AIR/FUEL RATIO
When troubleshooting idle quality or driveability complaints, it is necessary to consider the following:

^ INJECTOR SPRAY PATTERN
^ PRESENCE OF UNMETERED AIR LEAKS
^ EVAPORATIVE PURGE SYSTEM
^ RESTRICTED INTAKE SYSTEM
^ EXCESSIVE ENGINE OIL DILUTION
^ SUBSTANDARD FUEL OR UNAPPROVED ADDITIVES
^ CARBON BUILD-UP