Checking the Basics

All troubleshooting must begin by "CHECKING THE BASICS". Certain basic faults can be undetectable by the self-diagnostic system of the knock sensor control unit and in some cases can actually interfere with the self-checking and fault memory operation.

Low battery voltage, for example, can cause erroneous faults to set in control unit fault memories or can cause a system to go "Fail Safe" without setting a fault in memory. Also, testing procedures done on a running engine will cause malfunctions to be stored that were caused by a simulation or a disconnected circuit. On the other hand, system fault memories are cleared whenever the control unit or the battery is disconnected. Therefore, all fault memories should be read prior to any vehicle power interruption or troubleshooting. This will ensure that the technician can differentiate between actual malfunctions and "simulated malfunctions. Refer to COMPUTERIZED ENGINE CONTROLS for fault code retrieval (California only) and the corresponding testing procedures.
After testing is completed, the malfunction memory of the knock sensor control unit must be cleared.

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.

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

NOTE: Always inquire about accident history. Vehicles with a history of accident damage and repair, may be exhibit very unusual symptoms.

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.

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

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

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.

POWER SUPPLY RELAYS
Fuel pump and engine control 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.

FUEL DELIVERY AND 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.

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.

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
^ EXCESSIVE ENGINE OIL DILUTION
^ SUBSTANDARD FUEL OR UNAPPROVED ADDITIVES
^ CARBON BUILD-UP