CONDITION POSSIBLE CAUSE CORRECTION
ENGINE MISSES ON
ACCELERATION1. Dirty or incorrectly gapped spark
plugs.1. Clean spark plugs and set gap.
Refer to Group 8D, Ignition System.
2. Contamination in Fuel System. 2. Clean fuel system and replace
fuel filter.
3. Burned, warped, or pitted valves. 3. Replace valves.
4. Faulty coil(s). 4. Test and replace as necessary.
Refer to Group 8D, Ignition System.
ENGINE MISSES AT HIGH SPEED 1. Dirty or incorrect spark plug gap. 1. Clean spark plugs and set gap.
Refer to Group 8D, Ignition System.
2. Faulty coil(s). 2. Test and replace as necessary.
Refer to Group 8D, Ignition System.
3. Dirty fuel injector(s). Test and replace as necessary.
Refer to Group 14, Fuel System.
4. Contamination in fuel system. 4. Clean system and replace fuel
filter.
ENGINE DIAGNOSISÐMECHANICAL
CONDITION POSSIBLE CAUSES CORRECTION
NOISY VALVES 1. High or low oil level in
crankcase.1. Check and correct engine oil
level.
2. Thin or diluted oil. 2. Change oil to correct viscosity.
3. Low oil pressure. 3. Check and correct engine oil
level.
4. Dirt in tappets/lash adjusters. 4. Replace rocker arm/hydraulic
lash adjuster assembly.
5. Worn rocker arms. 5. Inspect oil supply to rocker arms.
6. Worn tappets/lash adjusters. 6. Install new rocker arm/hydraulic
lash adjuster assembly.
7. Worn valve guides. 7. Ream guides and install new
valves with oversize stems.
8. Excessive runout of valve seats
on valve faces.8. Grind valve seats and valves.
9. Missing adjuster pivot. 9. Replace rocker arm/hydraulic
lash adjuster assembly.
CONNECTING ROD NOISE 1. Insufficient oil supply. 1. Check engine oil level.
2. Low oil pressure. 2. Check engine oil level. Inspect oil
pump relief valve and spring.
3. Thin or diluted oil. 3. Change oil to correct viscosity.
4. Excessive bearing clearance. 4. Measure bearings for correct
clearance. Repair as necessary.
5. Connecting rod journal
out-of-round.5. Replace crankshaft or grind
surface.
6. Misaligned connecting rods. 6. Replace bent connecting rods.
9 - 12 ENGINEPL
DIAGNOSIS AND TESTING (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
OIL CONSUMPTION OR SPARK
PLUGS FOULED1. PCV system malfunction. 1. Check system and repair as
necessary. Refer to Group 25,
Emission Control Systems.
2. Worn, scuffed or broken rings. 2. Hone cylinder bores. Install new
rings.
3. Carbon in oil ring slots. 3. Install new rings.
4. Rings fitted too tightly in grooves. 4. Remove rings and check
grooves. If groove is not proper
width, replace piston.
5. Worn valve guide(s). 5. Ream guide(s) and replace
valve(s) with oversize valve(s) and
seal(s).
6. Valve stem seal(s) worn or
damaged.6. Replace seal(s).
9 - 14 ENGINEPL
DIAGNOSIS AND TESTING (Continued)
