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.
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/CAUSES
To trouble shoot following symptoms, refer to appropriate number under PROBABLE CAUSES.
| Symptom | Check Probable Causes |
|---|---|
| ENGINE LACKS POWER | No. 1, 3, 4, 6-11 and 16-20 |
| BLACK SMOKE | No. 2-4, 6-11 and 16-20 |
| BLUE SMOKE | No. 2, 6-8, 13-15 and 17-20 |
| EXCESSIVE OIL CONSUMPTION | No. 2, 6-8, 13-15 and 17-20 |
| NOISY OPERATION | No. 1-8, 11-12 and 19-20 |
| CYCLIC SOUND FROM TURBOCHARGER | No. 2, 19 and 20 |
| OIL LEAK AT TURBINE SEAL | No. 13-15 and 17-20 |
| OIL LEAK AT COMPRESSOR SEAL | No. 2, 8-11, 13-15 and 17-20 |
| (1) See PROBABLE CAUSES table. | |
| (1) | See PROBABLE CAUSES table. |
SYMPTOM TO PROBABLE CAUSES (1)
| Cause No. | Cause |
|---|---|
| 1 | Clogged air filter element. |
| 2 | Obstructed air intake duct to turbo compressor. |
| 3 | Obstructed air outlet duct from compressor to intake manifold. |
| 4 | Obstructed intake manifold. |
| 5 | Air leak in duct from air cleaner to compressor. |
| 6 | Air leak in duct from compressor to intake manifold. |
| 7 | Air leak at intake manifold-to-engine joint. |
| 8 | Obstruction in exhaust manifold. |
| 9 | Obstruction in exhaust system. |
| 10 | Gas leak in exhaust manifold-to-engine joint. |
| 11 | Gas leak in turbine inlet-to-exhaust manifold joint. |
| 12 | Gas leak in ducts after turbine outlet. |
| 13 | Obstructed turbocharger oil drain line. |
| 14 | Obstructed engine crankcase ventilation. |
| 15 | Turbocharger center housing sludged or coked. |
| 16 | Engine camshaft timing incorrect. |
| 17 | Worn engine piston rings or liners (blow-by). |
| 18 | Internal engine problems (valves, pistons). |
| 19 | Dirt caked on compressor wheel and/or diffused vanes. |
| 20 | Damaged turbocharger. |
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.