Riviera V6-231 3.8L Turbo VIN 3 4-bbl (1982)
MODELS AFFECTED:
1981-82 3.8L, V-6
An occasional light spark knock while accelerating or driving up hills should be no cause for concern. Under this mode, light spark knock indicates that
the greatest fuel economy is being achieved.
Two other conditions where the engine might spark knock, but would be considered normal are:
A.
At idle with a quick throttle opening; 2 or 3 cylinders may knock until the ECM re-adjusts timing.
B.
During medium throttle opening, when throttle is rapidly closed; 2 or 3 cylinders may knock until the ECM re-adjusts timing.
Engine spark knock, other than described above, is abnormal and can be corrected. Normally, three things cause an engine to spark knock.
1.
Fuel octane rating below requirements.
2.
Incorrect ignition timing.
3.
Lean fuel mixture; incorrect EGR operation.
Although it is not common, an abnormally high compression ratio can cause the engine to spark knock at wide open throttle. This spark knock may also
be heard under light throttle. Spark knock under these conditions is generally caused by excessive carbon build-up on the piston or cylinder head. A can
of GM Top Engine Cleaner or equivalent, when properly used, should correct spark knock caused by carbon build-up. If the condition returns, determine
what is causing the excessive carbon build-up. Leaking intake valve stem seals should not be overlooked.
FUEL
This engine is designed to operate on a fuel with, and octane rating of 87; anything less can cause engine spark knock. (See Owner's Manual for an
explanation of octane rating and high altitude octane rating).
IGNITION TIMING
Excessively advanced ignition timing can cause a ping or spark knock condition. This knock is the result of premature combustion of the air fuel mixture
working against the rotation of the engine.
ITEMS WHICH CAN AFFECT IGNITION TIMING AND CAUSE SPARK KNOCK
1.
Base ignition timing too far advanced.
2.
Abnormally high engine operatihg temperature.
3.
Check for proper operation of:
^
Coolant Sensor
^
Map Sensor
^
Baro Sensor
4.
Check for correct distributor wave washer.
5.
Unshielded EST wiring must be routed at least one inch from any spark wire.
ITEMS WHICH MAY CAUSE A LEAN FUEL MIXTURE
EGR System:
1.
The EGR system is designed to introduce exhaust gases through the intake manifold into the engine cylinders. These exhaust gases lower the
combustion temperatures which in turn reduce oxides of nitrogen to an acceptable level. Therefore, improper EGR system operation can cause a
lean air fuel mixture which permits excessively high combustion temperatures to develop. The excessively high combustion temperatures result in
the igniting of the lean air fuel mixture prior to spark plug firing, causing the engine to ping or spark knock.
Check for:
^
Proper operation of EGR control solenoid.
^
Proper operation of EGR cutout relay.
Stall testing the engine with foot on brake pedal will cause EGR cutout relay to energize and cutout EGR, causing engine to spark knock. This is a
normal condition.
