Checks
| Actions
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DEFINITION: Fuel ignites in the intake manifold, or in the exhaust
system, making loud popping noise.
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Preliminary Checks
|
| • | Refer to Important Preliminary Checks Before Starting in
Symptoms
. |
| • | Check PCM grounds for being clean, tight and in their proper locations. |
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Fuel
System
|
| • | Check for restricted fuel filter. |
| • | Check each injector harness is connected to the correct injector/cylinder
according to the firing order. Relocate injector harnesses as necessary. |
|
Sensor/System
|
| • | Check EGR for being loose or for a faulty gasket. Check EGR operation
for being open all the time. |
| • | Check Intake Air system and crankcase for air leaks. |
| • | Check Crankcase ventilation valve for proper operation. Place
finger over inlet hole in valve end several times. Valve should snap back.
If not, replace valve. |
| • | Check for proper calibration of speedometer. Connect Signal Generator
(J 33431-B) to VSS electrical connector. Ignition ON, tester ON and
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. |
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Ignition
System
|
| • | Check for proper ignition voltage output with spark tester J 26792.
Refer to
Restricted Exhaust
. |
| • | Check for an intermittent ignition system malfunction in the following
circuits: |
| - | Intermittent 4X circuit. |
| - | Intermittent 24X circuit. |
| - | Intermittent Ignition Control circuit. |
| - | Using the scan tools Snapshot feature may help locate an intermittent
ignition failure. Abnormal signals can cause a backfire on acceleration. |
Remove spark plugs and check for the following:
An improper spark plug gap will cause a driveability problem. Measure
and adjust the gap of the spark plugs. Refer to
Spark Plug Replacement
in Engine Electrical. If spark plugs are
gas or oil fouled, the cause of the fouling must be determined before
replacing the spark plugs.
Visually/Physically inspect Secondary ignition for the following:
| • | Ignition wires for cross firing. |
| • | Ignition wires arcing to ground. |
| • | Ignition wires for proper routing. |
| • | Ignition Coils for cracks or carbon tracking. |
| • | Wetting down the secondary ignition system with water from a spray
bottle may help locate damaged or deteriorated components. Look/listen for
arcing or misfiring as water is applied. |
| • | Check for loose ignition control module ground. |
|
Engine
Cooling System
|
| • | Check engine coolant level for being low. |
| • | Check engine thermostat for proper operation or for wrong heat
range. Refer to
Thermostat Diagnosis
in Engine Cooling. |
|
Engine
Mechanical
| Check engine mechanical:
| • | Sticking or leaking valves. |
| • | Excessive oil in combustion chamber-Leaking valve seals. |
| • | Low cylinder compression. |
For incorrect basic engine parts. Inspect the following:
|
Additional
Checks
|
| • | Visually (physically) check: Vacuum hoses for splits, kinks, and
proper connections and routing as shown on Vehicle Emission Control Information
label. |
| • | Check exhaust system for possible restriction. Check the following: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
| - | For possible plugged Three-Way catalytic converters by comparing
exhaust system back pressure on each side of engine. Refer to
Restricted Exhaust
in Engine Exhaust. |
| • | An engine miss condition can be caused by Electromagnetic Interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
engine RPM with a scan tool. A sudden increase in RPM with little
change in actual engine RPM change, indicates EMI is present. If a
problem exists, check routing of secondary ignition wires, high voltage
components (Near Ignition Control circuits). |
| • | Check PNP switch circuit and be sure the scan tool indicates vehicle
is in drive with gear selector in drive or overdrive. |
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