Checking the Basics and Visual Inspection

CHECKING THE BASICS

All troubleshooting must begin by inspection of basic items of engine operation. Some faults can be undetectable by the self-diagnostic systems of the engine control module and in some cases can actually interfere with the self-diagnosis and diagnostic trouble code memory operation.

Since diagnostic trouble codes are cleared whenever the engine control module or the battery is disconnected, all fault codes should be read prior to any vehicle power interruption or troubleshooting. Remember a diagnostic trouble code points to the involved system, not necessarily the component.

It is recommended the following items ALWAYS be checked:

- Engine Vacuum: Minimum 13 inches of mercury, idling, in neutral.
- Ignition Timing: To specifications.
- Valve Timing: To specifications.
- Engine Compression: To specifications.
- Exhaust System: Must be free of restriction.
- Engine PCV System: Must flow freely.
- Torque Converter Stall Speed: To specifications.
- Power Brake Booster: No internal vacuum leaks.
- Fuel Contamination: High alcohol or water content.
- Fuel Injectors: Rough idle can be caused by a loose connector.
- Technical Service Bulletins: Any that may apply to vehicle.
- Engine Secondary Ignition Check: Any abnormal scope pattern.

Any one or more of these items can give a driveability related problem. They cannot be overlooked as possible causes.

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

BATTERY STATE OF CHARGE
- A battery in a state of partial discharge can have a dramatic effect on the engine control module and related components.

FUSE INTEGRITY
- Fuses are employed to prevent possible damage to electrical components and wiring harnesses. The fuses and their connections must be without dynamic resistance. Dynamic resistance can only be checked using the voltage drop method of testing.

POSITIVE BATTERY CONNECTIONS
- All Positive battery (+) connections must be clean, tight, and free of corrosion for trouble-free electronic system operation.

NEGATIVE BATTERY CONNECTIONS
- As all electrical circuits are a circle, all battery negative (-) 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 Positive side of the electrical system, the ground side should be checked dynamically using the voltage drop technique.

GROUND STRAPS
- Braided metal cables attached to the engine or transmission which appear overheated or discolored indicate the need to thoroughly test all ground connections.

POWER SUPPLY RELAYS
- The system relay as well as it's connector can be a source of intermittent operation which will not set a Diagnostic Trouble Code.

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

IGNITION 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, grease and corrosion.

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

SPARK PLUGS
- If out of specification, spark plugs can significantly impair engine performance.
- Spark plug type, condition and gap must verified according to specification.

AIR/FUEL RATIO
- Injector spray pattern quality.
- Presence of unmetered air leaks.
- Evaporative purge system.
- Excessive engine oil dilution.
- Substandard fuel or unapproved additives.
- Carbon build-up.

TESTING EQUIPMENT
- High quality testing equipment is essential if accurate results are expected.
- The use of faulty equipment will result in erroneous test results.
- Use only suitable test leads, terminals and probe tips.