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80 - 2
IGNITION SYSTEMS
•
I f necessary, refer to the appropriate engine f i r i n g
d i a g r a m (Fig. 2 or Fig. 3).
Fig. 2 Engine Firing Order—3.9L
J908D-49
Fig. 3 Engine Firing Order—5.2L and 5.9L
DISTRIBUTOR ROTOR
Replace t h e rotor i f i t is cracked or i f the s p r i n g
t e r m i n a l does not have proper tension (Fig. 4).
A black silicone varnish covers the t i p of the rotor
electrode ( i n previous
years silicone
grease was
used).
The coating
is used
t o suppress
electro-
magnetic r a d i a t i o n . The coating w i l l d a r k e n w i t h age
and have a n ash l i k e appearance. T h e ash f o r m a t i o n
is n o r m a l and does affect engine performance.
SPARK PLUG CABLES
Spark Plug cables are sometimes referred to as sec-
ondary i g n i t i o n wires. The wires transfer electrical
current from t h e distributor t o i n d i v i d u a l spark
plugs a t each cylinder. The spark p l u g cables are o f
nonmetallic construction and have a b u i l t i n resis-
tance. The cables provide suppression o f radio fre-
quency emissions from the i g n i t i o n system.
INSUFFICIENT
SPRING
TENSION
CORRODED
EVIDENCE OF
PHYSICAL
CONTACT
W
I
T
H
C
A
P
J908D-48
Fig. 4 Distributor Rotor Inspection—Typical
Check the high-tension cable connections for good
contact a t t h e i g n i t i o n coil, d i s t r i b u t o r cap towers
and spark plugs. T e r m i n a l s should be f u l l y seated.
The t e r m i n a l s and covers should be i n good condi-
t i o n . T e r m i n a l s should f i t t i g h t l y t o the i g n i t i o n coil,
d i s t r i b u t o r cap, and spark plugs. T h e cover (boot) o f
t h e cable should f i t t i g h t a r o u n d the coil tower, dis-
t r i b u t o r tower and spark p l u g insulator. Loose cable
connections can cause corrosion and increase resis-
tance r e s u l t i n g i n shorter cable service life. To m a i n -
t a i n proper sealing a t t h e t e r m i n a l connections, t h e
connections should n o t be broken unless they are
damaged or testing indicates t h a t h i g h resistance, a n
open c i r c u i t , or other damage.
Clean h i g h tension cables w i t h a cloth moistened
w i t h a nonflammable solvent and wipe dry. Check
for b r i t t l e or cracked i n s u l a t i o n .
W h e n testing secondary cables for damage w i t h a n
oscilloscope, follow the i n s t r u c t i o n s o f the equipment
manufacturer.
I f a n oscilloscope is not available, spark p l u g cables
may be tested as follows:
W i t h the engine r u n n i n g , remove spark p l u g cable
f r o m spark p l u g (one a t a t i m e ) and hold next to en-
gine ground. I f the cable a n d spark p l u g are i n good
condition, the engine R P M w i l l drop and engine per-
formance w i l l decrease. I f engine R P M does not drop
the cable and/or spark p l u g is not operating properly
and should be replaced.
CAUTION: Do not leave any one spark plug cable
disconnected for longer than necessary during test-
ing or possible heat damage to the catalytic con-
verter may occur. Total test time must not exceed
ten minutes.
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