Dodge RAM TRUCK 1500 1995 Service Manual page 393

8D - 20 IGNITION SYSTEMS
BR
Check the high-tension cable connections for good
contact at the ignition coil, distributor cap towers
and spark plugs. Terminals should be fully seated.
The terminals and spark plug covers should be in
good condition. Terminals should fit tightly to the ig­
nition coil, distributor cap and spark plugs. The
spark plug cover (boot) of the cable should fit tight
around the spark plug insulator. Loose cable connec­
tions can cause corrosion and increase resistance, re­
sulting in shorter cable service life.
Clean the high tension cables with a cloth moist­
ened with a nonflammable solvent and wipe dry.
Check for brittle or cracked insulation.
When testing secondary cables for damage with an
oscilloscope, follow the instructions of the equipment
manufacturer. Note that 8.0L V-10 engines equipped
with distributor-less ignition will display opposite po­
larity spikes for paired cylinders.
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. If the cable and spark plug are
in good condition, the engine rpm should drop and
the engine will run poorly. If engine rpm does not
drop, the cable and/or spark plug may not be operat­
ing properly and should be replaced. Also check en­
gine 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. If 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.
3.9L/5.2L/5.9L Engines: Use an ohmmeter to test
for open circuits, excessive resistance or loose termi­
nals. Remove the distributor cap from the distributor.
Do not remove cables from cap. Remove cable
from spark plug. Connect ohmmeter to spark plug
terminal end of cable and to corresponding electrode
in distributor cap. Resistance should be 250 to 1000
Ohms per inch of cable. If not, remove cable from dis­
tributor cap tower and connect ohmmeter to the ter­
minal ends of cable. If resistance is not within
specifications as found in the Spark Plug Cable Re­
sistance chart, replace the cable. Test all spark plug
cables in this manner.
SHARK PLUG CABLE RESISTANCE
MINIMUM
250 Ohms Per Inch
1000 Ohms Per Inch
3000 Ohms Per Foot 12,000 Ohms Per Foot
J908D-43
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. If 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.
For removal and installation of spark plug cables,
refer to Spark Plug Secondary Cables in the Compo­
nent Removal/Installation section.
OXYGEN SENSOR (02S) TESTS
For an operational description, diagnosis and re­
moval or installation of the 02S, refer to Group 14,
Fuel Systems in this manual.
0N-B0ARD DIAGNOSTICS
mm CERTAIN IGNITION SYSTEM
COMPONENTS
The powertrain control module (PCM) performs an
On-Board Diagnostic (OBD) check for certain ignition
system components on all vehicles. This is done by
setting a diagnostic trouble code (DTC).
A DTC can be obtained in two different ways. One
of the ways is by connecting the DRB scan tool to the
data link connector. This connector is located in the
engine compartment (Fig. 34). Refer to the appropri­
ate Powertrain Diagnostic Procedures service manual
for operation of the DRB scan tool. The other way is
to cycle the ignition key and observe the malfunction
indicator lamp (MIL). The MIL lamp is displayed on
the instrument panel as the CHECK ENGINE lamp
(Fig. 35). This lamp will flash a numeric code. If a
numeric code number 11 (for the crankshaft position
sensor), 42 (for the ASD relay), or 43 (for the ignition
coil, V-10 engine only) is observed, a problem has
been found in the ignition system.
Note that the CHECK ENGINE lamp will illumi­
nate initially for approximately two seconds each
time the ignition key is turned to the ON position.
This is done for a bulb test.