Initial Inspection and Diagnostic Overview

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

1. NO FUEL IN TANK
Do not rely on the gauge or customer. Remove the gas cap and bounce or rock the vehicle and listen for fuel sloshing or if in doubt, add a few gallons.

2. A CLOGGED OR PARTIALLY RESTRICTED FUEL FILTER OR FUEL LINES
Several auto makers now use more than one filter. There is usually a screen on the fuel pick-up tube in the fuel tank that may also clog.

3. AN OPEN FUSE OR FUSE LINK
All electrical circuits are protected with a fuse or fuse link. Some fuses protect more circuits than may be listed on the fuse panel cover. Always check all fuses and fuse links.

4. BATTERY VOLTAGE
Electrical components used in the fuel system have a minimum voltage requirement to operate properly. If the cranking or operating voltage of the battery drops below 9.5 volts, some components may not operate properly.

5. DIRTY, RESTRICTED OR MISSING AIR FILTER ELEMENT
Many of todays engines are designed to compensate for amount of restriction that a clean air filter element normally creates. A minor 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 abnormally.

6. 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.

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

8. SATURATED CHARCOAL CANISTER
A charcoal canister that is saturated with fuel can cause an overly rich air fuel mixture. This may cause the computer system to malfunction.

9. FUEL DILUTED ENGINE OIL
If an engine has been operating in 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.

11. IMPROPER FUEL PRESSURE
High fuel pressure can cause excess fuel delivery, causing a rich air fuel mixture. Low fuel pressure can cause insufficient fuel delivery, causing a lean air fuel mixture.

12. DISCONNECTED OR LOOSE INJECTOR OR SOLENOID TERMINAL
A loose or poor connection 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.

13. CONTAMINATED OR WRONG FUEL
Dirty fuel. Water in fuel. Excessive alcohol content. Diesel fuel being used in a gasoline engine or visa versa. All of these can cause a variety of driveability problems.