Checks
| Actions
|
DEFINITION: Fuel ignites in the intake manifold, or in the exhaust
system, making loud popping noise.
|
Preliminary Checks
|
| • | Refer to
Symptoms
,
Important Preliminary Checks Before Starting. |
| • | Check the PCM grounds for being clean, tight and in their proper
locations. |
|
Fuel System
|
| • | Check for a restricted fuel filter. |
| • | Check that each injector harness is connected to the correct injector/cylinder
according to the firing order. Relocate injector harnesses as necessary. |
|
Sensor/System
|
| • | Check the EGR valve for being loose or for a faulty gasket. Check
the EGR valve for being open all the time. |
| • | Check the air intake system and crankcase for air leaks. |
| • | Check the crankcase ventilation valve for proper operation. Place
a finger over the inlet hole in the valve end several times. The valve should
snap back. If not, replace valve. |
| • | Check for proper speedometer calibration. Connect Signal Generator
(J 33431-B) to the VSS electrical connector. With the ignition on and
the tester on, monitor the speedometer. The speedometer should indicate
the speed being generated. |
| • | Using a scan tool, monitor TP sensor voltage. The TP sensor voltage
should be less then 0.9 volts at rest. If the TP sensor voltage is greater
than 0.9 volt, inspect the throttle body and accelerator cables for binding. |
| • | Using a scan tool, monitor KS system for excessive spark retard
activity. |
|
Ignition System
| Remove the spark plugs and check for the following:
| | An improper spark plug gap will cause a driveability problem. The spark
plug gapping should be done using a wire gauge gap tool (J 41319). |
If spark plugs are gas or oil fouled, the cause of the fouling must
be determined before replacing the spark plugs.
Check the plugs/coils for signs of arcing, cracks or carbon tracking.
| • | Check for loose ignition control module grounds. |
| • | Check the spark plugs for proper heat range. |
|
Engine Cooling System
|
| • | Check the engine coolant level for being low. |
| • | Check the engine thermostat for proper operation or for the wrong
heat range. Refer to
Thermostat Diagnosis
in Engine Cooling. |
|
Engine Mechanical
| Check for the following conditions:
| • | Excessive oil in combustion chamber may indicate leaking valve
seals. Refer to Oil Consumption Diagnosis
. |
| • | Low cylinder compression. Refer to Engine Compression Test
. |
| • | Incorrect basic engine parts. Inspect the following: |
Refer to Base Engine Misfire Diagnosis
.
|
Additional Checks
|
| • | Visually / physically check: Vacuum hoses for splits, kinks, and
proper connections and routing as shown on Vehicle Emission Control Information
label. |
| • | Check for improper harness routing. An engine miss condition
can be caused by Electromagnetic Interference (EMI) on some engine controls
circuits. Use the scan tool to check for erratic sensor values or excessive
changes in indicated RPM with little change in actual engine RPM. This
may indicate EMI is present. If a problem exists, check for improper routing
of the harness near high voltage components (Ignition Components) or high
current components (alternator, motors, solenoids etc.). |
| • | Check the charging system. a bad diode in the alternator can
allow AC noise to enter the electrical system. This may affect the engine
controls system operation. Refer to
Charging System Check
. |
| • | Check the Trans Range switch circuit and be sure the scan tool
indicates vehicle is in drive with gear selector in drive or overdrive. |
|
