VISUAL INSPECTION
Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not pinched or cut. See VACUUM DIAGRAMS article in this section to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.
MECHANICAL INSPECTION
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate engine's oiling system. |
Diagnostic Aids
Water or foreign material in fuel can cause a no-start condition during freezing weather. Engine may start after 5-6 minutes in a heated shop. Problem may not reoccur until vehicle is parked overnight in freezing temperatures. Ensure connections are not contaminated, corroded or damaged.
Low fuel pressure can result in very lean air/fuel ratio. Fouled or damaged spark plugs will also cause "engine cranks but will not run" condition.
Scheme 1
Scheme 2
Fuel spray may exist at fuel injector, but it may not be enough to start engine. If both fuel injector and circuit are okay, fuel injector nozzle may be partly blocked.
Scheme 3
Scheme 4
Visually inspect wiring and connectors if intermittent problem exists.
Scheme 5
Scheme 6
CHART A-7B, FUEL SYS DIAGNOSIS (FUEL PRESSURE CHECK)
When ignition is turned on, ECM will turn on in-tank fuel pump. Fuel pump will stay on as long as engine is cranking or running and ECM is receiving reference pulses. If no reference pulses are received by ECM, ECM will shut off fuel pump about 3 seconds after ignition is turned on or when engine stops.
Fuel pump will deliver fuel to fuel rail and injectors, then to pressure regulator, where system pressure is controlled to about 23-31 psi (1.6-2.2 kg/cm 2 ) depending on engine operating conditions. Excess fuel is then returned to fuel tank.
Note. Test numbers refer to numbers on diagnostic chart.
- Checks if fuel system pressure is within specifications.
- Checks fuel feed pipe and hose for leaks.
- Checks for faulty fuel pump or leaky fuel filter.
- Checks for leaky fuel injector or throttle body or faulty fuel pressure regulator.
- Checks for restricted fuel feed pipe, restricted fuel filter and faulty fuel pressure regulator.
- Determines if a restricted fuel return line or faulty fuel pressure regulator exists.
Improper fuel system pressure can result in one of following conditions
- Engine cranks, but will not run.
- Engine cuts out, may feel like ignition problem.
- Poor fuel economy, loss of power.
- Hard starts.
