Component Tests and General Diagnostics

Before attempting to diagnose or repair what might be wrong, always look for the obvious problem. Some common problems that are associated with the emission control system are:

1. DIRTY, RESTRICTED OR MISSING AIR FILTER ELEMENT
Many of todays engines are designed to compensate for the restriction that a clean air filter element normally creates. A major deviation from the normal air flow (too much from a missing element or too little from a dirty element) can cause the engine to operate outside of the range that the emission control system is designed to compensate for.

2. VACUUM LEAKS
Minor vacuum leaks at any point in the intake system can cause a lean mixture. Always confirm that all vacuum hoses are installed properly, check for leaks at manifold, throttle chamber, ducting and injectors. Check any point between the air intake and the cylinder head for leakage. In addition to checking for vacuum leaks, inspect the ducting (if applicable) between the airflow metering device and the throttle plate. Unmetered air entering through any leaks in this area will cause a lean mixture similar to a vacuum leak.

3. RESTRICTED EXHAUST
A partially restricted exhaust system can cause the engine to run out of the acceptable range for emissions or in severe cases, not at all. An exhaust leak may be an indication of a restriction down stream of the leak.

4. SATURATED CHARCOAL CANISTER
A charcoal canister that is saturated with fuel can cause an overly rich air fuel mixture. This condition can cause the engine to operate outside of the range that the emission control and computer system is designed to compensate for.

5. FUEL DILUTED ENGINE OIL
If an engine has been operating with an overly rich air fuel mixture, the chances that the engine oil has been diluted are great. If the oil smells like fuel or the level is above normal, suspect this problem. This condition can cause the engine to run rich enough to be out of acceptable range for emissions.

6. DISCONNECTED OR LOOSE TERMINALS
Loose or poor connections can cause a fuel injector to not operate at all times. This can cause an engine miss (most noticeable at idle) and excessive HC emissions. Likewise terminal connections on emission control equipment or sensors can cause erratic operation or send an incorrect signal to the ECU. During visual inspection it is also advisable to look for any loosely connected, corroded or damaged wire terminals or connections. Additionally look for any pinched or frayed wiring.