Checks
| Actions
|
DEFINITION:
Fuel ignites in the intake manifold, or in the exhaust system, making loud
popping noise.
|
Preliminary Checks
|
| • | Search for any bulletins. |
| • | Verify that the powertrain control module (PCM) grounds are clean,
tight, and in the correct locations. |
|
Fuel System
|
| • | Check for a restricted fuel filter. |
| • | Verify that each fuel injector harness is connected to the correct
injector and cylinder according to the firing order. Relocate any fuel injector
harnesses as necessary. |
|
Sensor and System
|
| • | Check the exhaust gas recirculation (EGR) valve for being loose
and for a faulty gasket. Check the EGR valve for being open all the time. |
| • | Check the air intake system and the crankcase for air leaks. |
| • | Check the crankcase ventilation valve for correct operation. Place
a finger over the inlet hole in the valve end several times. The valve should
snap back. If not, replace the valve. |
| • | Check for the correct speedometer calibration. Connect the J 33431-C
signal generator to
the vehicle speed sensor (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 the throttle position (TP) sensor voltage.
The TP sensor voltage should be less than 0.9 volt at rest. If the
TP sensor voltage is more than 0.9 volt, inspect the throttle body
and the accelerator cables for binding. |
| • | Using a scan tool, monitor the knock sensor (KS) system for any
excessive spark retard activity. |
|
Ignition System
| Remove the spark plugs and
check for the following conditions:
| | An improper spark plug gap will cause a driveability problem. The spark
plug gapping should be done with a wire gauge gap tool . |
If the spark plugs are gas or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs.
Check the plugs and the coils for signs of arcing, cracks, or carbon
tracking.
| • | Check for any loose ignition control module grounds. |
| • | Check the spark plugs for the correct heat range. |
|
Engine Cooling System
|
| • | Check for a low engine coolant level. |
|
Engine Mechanical
| Check for the following
conditions:
| • | Any excessive oil in the combustion chambers may indicate leaking
valve seals. Refer to
Oil Consumption Diagnosis
in Engine Mechanical. |
| • | Any incorrect basic engine parts--Inspect the following parts: |
Refer to
Symptoms - Engine Mechanical
in Engine Mechanical.
|
Additional Checks
|
| • | Visually and physically check the vacuum hoses for splits, kinks,
and the correct connections and routing as shown on the Vehicle Emission Control
Information label. |
| • | Check the exhaust system for a restriction. Refer to
Restricted Exhaust
in Engine Exhaust. |
| • | Check for any 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 any erratic sensor values or
excessive changes in the indicated RPM with little change in the actual
engine RPM. This may indicate EMI is present. If a problem exists, check
for an improper routing of the harness near high voltage components
or the high current components. |
| • | Check the charging system. A bad diode in the alternator can
allow A/C noise to enter the electrical system. This may affect the engine
controls system operation. Refer to
Diagnostic Starting Point - Engine Electrical
in Engine Electrical. |
| • | Check the transaxle range switch circuit and be sure the scan
tool indicates the vehicle is in drive with the gear selector in Drive or
in Overdrive. |
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