SYMPTOMS (GASOLINE)
Note. See SYMPTOMS (DIESEL) if necessary.
Symptom Definition
Engine cranks okay, but does not start for a long time. Engine eventually starts and may run okay or die immediately.
Engine starts okay but dies after brief idle, as soon as any load is placed on engine (such as turning on air conditioner or engaging transmission) or on initial drive-away.
Momentary lack of response when accelerator is pushed down. Can occur at any vehicle speed. Usually occurs after a stop.
Engine power varies under steady throttle or cruise. Feels like vehicle speeds up and slows down even though accelerator pedal position remains constant.
Engine delivers less power than expected. Little or no increase in speed when accelerator is pushed down.
Fuel ignites in intake manifold or in exhaust system, making a loud popping noise.
Cuts out, misses is defined as a steady pulsation or jerking following engine speed, usually more pronounced as engine load increases. Exhaust may have a steady spitting sound at idle or low speed. Perform careful visual inspection as described in BASIC TESTING article in this section.
Engine runs unevenly at idle. If bad enough, vehicle will shake. Idle RPM may vary. Engine idles at incorrect RPM.
Engine starts but will not run at idle. Engine runs if accelerator is held at part throttle.
Fuel economy, as measured by an actual road test, is noticeably lower than expected. Current fuel economy is noticeably lower than previous fuel economy.
Engine continues to run (but very rough) after ignition is turned off. If engine runs smoothly, check ignition switch.
A mild to severe ping, usually worse during acceleration. Engine makes sharp metallic knocks which change with degree of acceleration.
Vehicle fails emission test. Vehicle may also emit "rotten egg" smell (hydrogen sulfide) from exhaust pipe.
SYMPTOMS
To trouble shoot following symptoms, refer to appropriate number under PROBABLE CAUSES.
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplication of circuit or component failure in order to identify fault. These procedures may lead to computer recording a fault code which may help diagnosis.
If problem vehicle does not produce fault codes, use a DVOM to monitor voltage or resistance values while attempting to reproduce conditions which will create an intermittent fault. A change in status on DVOM indicates a fault has been located.
When using a voltmeter to pinpoint faults, monitor voltage reading with ignition on or vehicle running. A change in status on voltmeter while performing test procedure indicates area of fault. See TEST PROCEDURES under INTERMITTENTS.
When using an ohmmeter to detect problems in circuit, monitor circuit resistance (ohms) with ignition switch in OFF position or with battery disconnected. A change in ohmmeter reading while performing test procedure indicates area of fault. See TEST PROCEDURES under INTERMITTENTS.
SERVICE ENGINE SOON light comes on but does not stay on. A stored code may or may not exist.