5.0l
/ 305 cid / 5.7l / 350 cid ENGINES
SERVICE MANUAL NUMBER 24
Piston Failures
Pre-Ignition
Pre-ignition is abnormal fuel ignition caused by combustion chamber hot spots. Control of
the start of ignition is lost, as combustion pressure rises too early, causing power loss and
rough running. The upward motion on the piston is opposed by the pressure rise. This can
result in extensive damage to the internal parts from the high increase in combustion cham-
ber temperature.
72424
Pre-Ignition Damage
a
b
c
d
72314
a - Ignited By Hot Deposits
b - Regular Ignition Spark
c - Ignites Remaining Fuel
d - Flame Front Collide
PRE-IGNITION CAUSES
1.
Hot spots in the combustion chamber from glowing deposits (due to the use of improper
oils and/or fuels).
2.
3.
Overheated spark plug electrodes (improper heat range or defective plug).
Any other protuberance in the combustion chamber, such as an overhanging piece of
gasket, an improperly seated valve or any other inadequately cooled section of material
that could serve as a source for pre-ignition problems.
NOTE: Engine failures that result from the foregoing conditions are beyond the control of
Mercury MerCruiser. No warranty will apply to failures that occur under these conditions.
Index
Page 3A-16
90-861327--1 OCTOBER 1999
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 305 CID, Mercury MerCruiser 350 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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