TROUBLESHOOTING 285
Test and Procedure
Results and Indications
Proceed
to
4.7—Examine the location of all the
plugs.
The following diagrams illustrate some of the
conditions that the location of plugs will reveal.
4.8
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Two adjacent plugs are fouled in a
6-cylinder engine, 4-cylinder
engine or either bank of a V-8.
This is probably due to a blown
head gasket between the two cyl-
inders
The two center plugs in a 6-cylinder engine
are fouled. Raw fuel may be "boiled" out of
the carburetor into the intake manifold after
the engine is shut-off. Stop-start driving can
also foul the center plugs, due to overly rich
mixture. Proper float level, a new float needle
and seat or use of an insulating spacer may
help this problem
An unbalanced carburetor is indi-
cated. Following the fuel flow on
this particular design shows that
the cylinders fed by the right-hand
barrel are fouled from overly rich
mixture, while the cylinders fed
by the left-hand barrel are normal
O O
o o
If the four rear plugs are overheated, a cool-
ing system problem is suggested. A thorough
cleaning of the cooling system may restore
coolant circulation and cure the problem
2
O
4
O
6
O
8
O
9
o
3
9
•
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Finding one plug overheated may
indicate an intake manifold leak
near the affected cylinder. If the
overheated plug is the second of
two adjacent, consecutively firing
plugs, it could be the result of ig-
nition cross-firing. Separating the
leads to these two plugs will elimi-
nate cross-fire
Occasionally, the two rear plugs in large,
lightly used V-8's will become oil fouled.
High oil consumption and smoky exhaust may
also be noticed. It is probably due to plugged
oil drain holes in the rear of the cylinder
head, causing oil to be sucked in around the
valve stems. This usually occurs in the rear
cylinders first, because the engine slants that
way
