Electronic Ignition System Diagnosis
Diagnostic Instructions
Circuit/System Description
This ignition system uses individual Ignition Coil assemblies
for each cylinder. The engine control module (ECM) controls the
spark events by transmitting the timing pulses on the ignition
control circuits to the individual ignition coil assemblies in
firing order sequence. Each ignition coil has the following
circuits:
| • |
An ignition voltage
circuit |
| • |
An ignition control
circuit |
Diagnostic Aids
| • |
This test procedure requires
that the vehicle battery has passed a load test and is completely
charged. |
| • |
There is an adequate supply of
fuel in the fuel tank. |
| • |
When disconnecting electrical
connectors or removing fuses and relays from a fuse block, always
inspect both mating electrical terminals for corrosion and terminal
tightness. |
| • |
Use the EL 35616-E
Terminal Test Kit for any test that requires probing the
underbonnet fuse block terminals, component wire harness terminals,
or the ECM wire harness terminals. |
| • |
A slight to moderate
resistance in the ignition voltage circuit can cause a misfire
condition or a crank/no start concern. |
| • |
Extended engine cranking time,
will foul the spark plugs with excessive fuel and cause a crank/no
start condition. |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Electronic Ignition System Description
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Special Tools
| • |
EL 26792 HEI
Spark Tester |
| • |
EL 35616-E
Terminal Test Kit |
For equivalent regional tools, refer to
Special Tools for scan tool information
Circuit/System Verification
Note: Verify that the
engine is in good mechanical condition before continuing with this
diagnostic.
Observe the engine controls schematic for the ignition
module/coils, and review the ignition system specifications to
verify the following concerns:
| • |
The ignition modules/coils are
correctly wired and connected. |
| • |
The proper spark plug gap and
torque. |
| • |
The proper Ω values for
the spark plug wires. |
Circuit/System Testing
| 1. |
Turn OFF the ignition.
|
|
Note: If the ignition
fuse F3UA is open, it will be necessary to test the spliced
ignition circuits and the components for a short to ground.
|
| 2. |
Inspect the fuse that supplies
ignition voltage to the ignition module/coils. |
| ⇒ |
If fuse F3UA is open, test all ignition voltage
circuits to the T8 Ignition Coil for a short to ground. |
| 3. |
Disconnect the T8 Ignition
Coil connector. |
| 4. |
Replace the open fuse F3UA
with a new fuse. |
| 5. |
Ignition ON, engine
OFF. |
| 6. |
Reconnect T8 Ignition Coil
connector. |
| ⇒ |
If the fuse F3UA opens when connecting the T8
Ignition Coil, then replace the T8 Ignition Coil. |
| 7. |
Ignition OFF, disconnect the
T8 Ignition Coil electrical connector. |
| 8. |
Ignition ON, verify that a
test lamp illuminates between the ignition voltage circuit terminal
A and ground. |
| ⇒ |
If the test lamp does not illuminate test the T8
Ignition Coil Ignition Voltage Circuit for an open/high resistance
or a short to ground. |
| 9. |
Verify that a test lamp
illuminates between the T8 Ignition Coil Ground Circuit terminal B
and B+. |
| ⇒ |
If the test lamp does not illuminate, test the T8
Ignition Coil Ground Circuit for an open/high resistance. |
| 10. |
Exchange the affected T8
Ignition Coil assembly with a known good assembly. |
|
Note: An open/high
resistance on the low reference circuit to the ignition control
module may cause a misfire.
|
| 11. |
Start and idle the engine.
Observe the misfire counters on the scan tool. |
| ⇒ |
If the misfire or crank/no start is resolved,
replace the T8 Ignition Coil/module assembly. |
| ⇒ |
If the misfire does not transfer with the suspect
T8 Ignition Coil, measure the resistance of the ignition control
circuit. The ignition control circuit should measure less than 5
Ω. If the circuit tests normal, replace the K20 Engine
Control Module. |
Component Testing
Static Test
| • |
Use the spark plug inspection
procedure to verify the integrity of the spark plugs. Replace the
spark plug if necessary. |
|
Note: An erratic or
weak spark is considered a no spark condition.
|
| • |
Use the EL 26792
HEI Spark Tester to verify the output of the T8 Ignition
Coil. If no spark is detected across the gap of the spark plug
tester, replace the T8 Ignition Coil assembly. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
|
