Spark Plug Service - DaimlerChrysler LH New Yorker 1994 Electronic Service Manual

8D - 12 IGNITION SYSTEMS
TESTING—ALL ENGINES
When testing cables for punctures and cracks with
an oscilloscope, follow the instructions of the equip-
ment manufacturers.
CAUTION: Do not leave any one spark plug cable
disconnected any longer than necessary during test
or possible heat damage to catalytic converter will
occur. Total test time must not exceed ten minutes.
If an oscilloscope is not available, test cables as
follows:
(1) With the engine not running, connect one end of
a test probe (i.e. a piece of wire with insulated alliga-
tor clips on each end) to a good ground, other end free
for probing.
WARNING: THE DIRECT IGNITION SYSTEM GENER-
ATES APPROXIMATELY 40,000 VOLTS. PERSONAL
INJURY COULD RESULT FROM CONTACT WITH
THIS SYSTEM.
(2) With engine running, move test probe along
entire length of all cables (approximately 0 to 1/8 inch
gap). If punctures or cracks are present there will be
a noticeable spark jump from the faulty area to the
probe. Cracked, leaking or faulty cables should be
replaced.
(3) Use an ohmmeter to check cables for opens,
loose terminals or high resistance.
(a) Remove cable from spark plug.
(b) Remove cable from the coil tower.
(c) Connect the ohmmeter between spark plug
end terminal and the coil end terminal. Resistance
should be within tolerance shown in the cable resis-
tance chart. If resistance is not within tolerance,
replace cable assembly. Test all spark plug cables in
same manner.
CABLE RESISTANCE CHART

SPARK PLUG SERVICE

When replacing the spark plug cables, route the
cables correctly and secure them in the appropriate
retainers. Failure to route the cables properly can
cause the radio to reproduce ignition noise, cross igni-
tion of the spark plugs or short circuit the cables to
ground.
Never wire brush spark plugs. The spark plug
insulator tip is harder than the bristles of wire
brushes. Bristles of wire brushes can leave a conduc-
tive, metallic film on the insulator which could lead to
conductive deposits. Conductive deposits can cause
spark plug failure and engine misfire. Use a jewelers
file to remove deposits from the electrode gap. Use a
spark plug cleaning machine to clean spark plugs.
SPARK PLUG REMOVAL
Always remove the spark plug cable by grasping at
the spark plug boot, turning the boot 1/2 turn and
pulling straight back in a steady motion.
(1) Prior to removing the spark plug spray com-
pressed air around the spark plug hole and the area
around the spark plug.
(2) Remove the spark plug using a quality socket
with a rubber or foam insert.
(3) Inspect the spark plug condition. Refer to Spark
Plug Condition in this section.
SPARK PLUG GAP ADJUSTMENT
Check the spark plug gap with a gap gauge. If the
gap is not correct, adjust it by bending the ground
electrode (Fig. 7).
Fig. 7 Setting Spark Plug Gap—Typical
SPARK PLUG INSTALLATION
(1) To avoid cross threading, start the spark plug
into the cylinder head by hand.
(2) Tighten spark plugs to 28 N m (20 ft. lbs.)
torque.
(3) Install spark plug cables over spark plugs. On
3.5L engines, ensure the top of the spark plug insula-
tor seals the upper end of the spark plug tube.
SPARK PLUG TUBES—3.5L ENGINE
On 3.5L engines, the spark plugs thread into the
top of cylinders. Tubes isolate the spark plugs and
cables. For spark plug tube service, refer to Group 9,
Engines.