Dodge ram truck 3500 1996 Service Manual page 396

8D 14 IGNITION SYSTEM
B R
D I A G N O S I S A N D T E S T I N G (Continued)
ENGINE COOLANT TEMPERATURE SENSOR
For an operational description, diagnosis and
removal/installation procedures, refer to Group 14,
Fuel System.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
For an operational description, diagnosis and
removal/installation procedures, refer to Group 14,
Fuel System.
SPARK PLUG CABLES
Check the spark plug cable connections for good
contact at the coil(s), distributor cap towers, and
spark plugs. Terminals should be fully seated. The
insulators should be in good condition and should fit
tightly on the coil, distributor and spark plugs. Spark
plug cables with insulators that are cracked or torn
must be replaced.
Clean high voltage ignition cables with a cloth
moistened with a non-flammable solvent. Wipe the
cables dry. Check for brittle or cracked insulation.
On 3.9L/5.2L/5.9L engines, spark plug cable heat
shields are pressed into the cylinder head to sur­
round each spark plug cable boot and spark plug
(Fig. 31). These shields protect the spark plug boots
from damage (due to intense engine heat generated
by the exhaust manifolds) and should not be
removed. After the spark plug cable has been
installed, the lip of the cable boot should have a
small air gap to the top of the heat shield (Fig. 31).
Fig. 31 Heat Shields—3.9U5.2U5.9L Engines
TESTING
When testing secondary cables for damage with an
oscilloscope, follow the instructions of the equipment
manufacturer.
If an oscilloscope is not available, spark plug cables
may be tested as follows:
CAUTION: Do not leave any one spark plug cable
disconnected for longer than necessary during test­
ing. This may cause possible heat damage to the
catalytic converter. Total test time must not exceed
ten minutes.
With the engine running, remove spark plug cable
from spark plug (one at a time) and hold next to a
good engine ground. I f the cable and spark plug are
in good condition, the engine rpm should drop and
the engine will run poorly. I f engine rpm does not
drop, the cable and/or spark plug may not be operat­
ing properly and should be replaced. Also check
engine cylinder compression.
With the engine not running, connect one end of a
test probe to a good ground. Start the engine and run
the other end of the test probe along the entire
length of all spark plug cables. I f cables are cracked
or punctured, there will be a noticeable spark jump
from the damaged area to the test probe. The cable
running from the ignition coil to the distributor cap
can be checked in the same manner. Cracked, dam­
aged or faulty cables should be replaced with resis­
tance type cable. This can be identified by the words
ELECTRONIC SUPPRESSION printed on the cable
jacket.
Use an ohmmeter to test for open circuits, exces­
sive resistance or loose terminals. I f equipped,
remove the distributor cap from the distributor. Do
not remove cables from cap. Remove cable from
spark plug. Connect ohmmeter to spark plug termi­
nal end of cable and to corresponding electrode in
distributor cap. Resistance should be 250 to 1000
Ohms per inch of cable. I f not, remove cable from dis­
tributor cap tower and connect ohmmeter to the ter­
minal ends of cable. I f resistance is not within
specifications as found in the Spark Plug Cable
Resistance chart, replace the cable. Test all spark
plug cables in this manner.
MINIMUM MAXIMUM
250 Ohms Per Inch
1000 Ohms Per Inch
3000 Ohms Per Foot
12,000 Ohms Per Foot
J908D-43
SPARK PLUG CABLE RESISTANCE
To test ignition coil-to-distributor cap cable, do not
remove the cable from the cap. Connect ohmmeter to
rotor button (center contact) of distributor cap and
terminal at ignition coil end of cable. I f resistance is
not within specifications as found in the Spark Plug
Cable Resistance chart, remove the cable from the
distributor cap. Connect the ohmmeter to the termi­
nal ends of the cable. If resistance is not within spec­
ifications as found in the Spark Plug Cable
Resistance chart, replace the cable. Inspect the igni­
tion coil tower for cracks, burns or corrosion.