CONDITION POSSIBLE CAUSES CORRECTION
ENGINE STALLS OR
ROUGH IDLE
1. Carbon buildup on throttle plate. 1. Remove throttle body and de-carbon.
2. Engine idle speed too low. 2. Check Idle Air Control circuit. Refer to
the appropriate Diagnostic Information for
IAC motor testing.
3. Worn or incorrectly gapped spark
plugs.
3. Replace spark plugs or set gap.
4. Faulty or crossed ignition cables. 4. Check for correct firing order or replace
ignition cables as necessary.
5. Faulty coil(s). 5. Test and replace as necessary.
6. Intake manifold vacuum leak. 6. Inspect intake manifold gasket and vac-
uum hoses. Replace as necessary.
ENGINE MISSES ON
ACCELERATION
1. Worn or incorrectly gapped spark
plugs.
1. Replace spark plugs or set gap.
2. Faulty ignition cables. 2. Replace ignition cables as necessary.
3. Dirt or water in fuel system. 3. Clean system and replace fuel filter.
4. Burned, warped, or pitted valves. 4. Install new or reface valves as neces-
sary.
5. Faulty coil(s). 5. Test and replace as necessary.
ENGINE DIAGNOSIS - MECHANICAL
CONDITION POSSIBLE CAUSES CORRECTION
NOISY VALVES 1. High or low oil level in crank-
case.
1. Check for correct oil level. Adjust oil
level by draining or adding as needed.
2. Thin or diluted oil. 2. Change oil and filter.
3. Low oil pressure. 3. Check engine oil level. If OK, perform
oil pressure test. (Refer to 9 - ENGINE/
LUBRICATION - DIAGNOSIS AND TEST-
ING).
4. Dirt in tappets/lash adjusters. 4. Clean/replace hydraulic tappets/lash
adjusters.
5. Bent push rod(s). 5. Replace push rod(s) as necessary.
6. Worn rocker arms. 6. Replace worn rocker arms and inspect
oil supply to rocker arms.
7. Worn tappets/lash adjusters. 7. Replace hydraulic tappets/hydraulic lash
adjusters.
8. Worn valve guides. 8. Ream and install new valves with over-
size stems.
9. Excessive runout of valve seats
on valve faces.
9. Grind valve seats and valves.
ZB ENGINE 9 - 5
ENGINE - 8.3L (Continued)
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