Inspections
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DEFINITION: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
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Preliminary
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• | Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to
Engine Controls Schematics
. Ensure the resistance between the engine control module (ECM) housing
and the battery negative cable is less than 0.5 ohms. |
• | Verify that the ECM and ECM bracket fasteners are at the correct torque. |
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Fuel System
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• | Inspect that each injector harness is connected to the correct injector/cylinder according to the firing order. |
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Sensor/System
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• | Inspect the air intake system and the crankcase for air leaks. |
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Ignition System
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• | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. |
• | Remove the spark plugs and inspect for the following conditions: |
- | Refer to the following procedures: |
• | If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: |
- | For diagnosis of coolant contaminated spark plugs, refer to
Loss of Coolant
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• | Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. |
• | Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. |
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Engine Cooling System
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• | Inspect the engine thermostat for the correct operation and heat range. Refer to
Thermostat Diagnosis
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Engine Mechanical
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• | Inspect for the following engine mechanical conditions: |
- | Excessive oil in combustion chamber or leaking valve seals |
- | Incorrect cylinder compression |
- | Sticking or leaking valves |
- | Excessive carbon buildup in the combustion chambers--Clean the chambers with top engine cleaner. Follow the instructions on the can. |
- | For more information, refer to the following procedures: |
• | Inspect the following components for incorrect basic engine parts: |
- | Pistons, connecting rods, or bearings |
- | Refer to the following procedures: |
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Additional
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• | Inspect the vacuum hoses for splits and kinks. Verify that the connections and routing are as shown on Vehicle Emission Control Information. Refer to
Emission Hose Routing Diagram
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• | Inspect the intake manifold and the exhaust manifold passages for casting flash. |
• | Test the transmission torque converter clutch (TCC). The scan tool should indicate a drop in engine speed when the TCC is commanded ON. Refer to
Torque Converter Diagnosis
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• | Inspect the following exhaust system components: |
- | The exhaust system for damage |
- | The exhaust manifold for a collapsed inner wall |
- | The mufflers for heat distress or possible internal failure |
- | The three-way catalytic converters for restrictions |
• | Electromagnetic interference (EMI) on the CKP sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with
little change in actual engine speed indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits. |
• | Test the park neutral position (PNP) switch circuit. |
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