For 1990-2009 cars

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Engine Performance diagnostic procedures are covered in Engine Controls and should be consulted for diagnosis of any Driveability, Emissions, or Service Engine Soon lamp complaint.

• | Refer to Engine Controls - General Information.

• | Refer to Engine Controls - Fuel Injection (MFI). Check for any related service bulletins or service manual updates prior to extensive engine diagnosis.

Notice: The following diagnosis information covers common problems and possible causes. When the proper diagnosis is made, the problem should be corrected by adjustment, repair or part replacement as required. Refer to the appropriate section of the manual for these procedures

This diagnostic chart will assist in engine misfire diagnosis due to a mechanical problem such as a faulty camshaft or leaking headgasket. Base engine timing is assumed to be correct and, that acceptable fuel is being used. This chart will not identify a crossed injector wire, faulty injector, coil, driver, etc., or any other component failure or perceived misfire with no driveability symptoms (i.e. chipped reluctor ring with a DTC set or Service Engine Soon Light illuminated). The On-Board Diagnostic System Check must be performed first in order to ensure the correct chart is followed for diagnosis of a misfire. Refer to Engine Controls first, then, if necessary, refer to this chart.

1 | Are there any obvious mechanical noises? | -- | Go to Base Engine Misfire Diagnosis | Go to Step 2
2 | Visually inspect valve train components spark plugs, coils, integrated ignition components, and hoses for proper hook up or damage. Is there any damaged component or improperly connected wires or hoses? | -- | Go to Step 3 | Go to Step 4
3 | Repair or replace the parts as necessary. Do the symptoms still exist? | -- | Go to Step 4 | System OK
4 | Remove and inspect the spark plugs. Are any spark plugs contaminated with the engine coolant? | -- | Go to Step 6 | Go to Step 5
5 | Are the spark plugs contaminated with engine oil? | -- | Go to Step 9 | Go to Step 12
6 | Check valve stem oil seals and valve guides for wear. | -- | Go to Step 7 | Go to Step 8
7 | Repair or replace valve stem oil seal and valve guides as necessary. | -- | Go to Step 8 | System OK
8 |

1. Remove and inspect the intake manifold and the intake manifold gasket. Refer to Intake Manifold Removal.
2. Replace the parts as necessary.

Do the symptoms still exist?

--

Go to Step 13

System OK

9 | Remove and inspect the intake manifold and the intake manifold gasket. Refer to Intake Manifold Removal. | -- | Go to Step 10 | Go to Step11
10 | Replace the parts as necessary Do the symptoms still exist? | -- | Go to Step 13 | System OK
11 | Remove and inspect the cylinder head. Refer to Cylinder Head Clean and Inspect. Are the valve guides or the seals damaged? | -- | Go to Step 11 | Go to Step 12
12 | Remove and inspect the piston, the piston rings, and the cylinder for wear. Are the piston components damaged? | -- | Go to Step 10 | Go to Step 13
13 | Perform a cylinder leak test. Does the engine pass the cylinder leakdown test? | -- | Go to Step 14 | Refer to Engine Unit Repair
14 |

1. Install a vacuum gauge to the intake manifold.
2. Measure the manifold vacuum with the engine at the idle and record the measurement.
3. Disconnect the vacuum lines from all of the openings of the manifold and the plug.
4. Inspect the manifold vacuum again with the engine at idle.

Are both vacuum readings the same?

--

Go to Step 16

Go to Step 15

15 | Inspect each vacuum operated accessory/vacuum line and repair any open or leaking components. Do the symptoms still exist? | -- | Go to Step 18 | System OK
16 | Using a spray bottle, lightly spray the ignition coil cover and housing while listening to the engine. Did the engine stumble or stall? | -- | Go to Step17 | Go to Step 18
17 | Replace the ignition coil, coil housing, or connectors. Do the symptoms still exist? | -- | Go to Step 18 | System OK
18 | Remove the intake manifold and carefully inspect the intake manifold gasket. Is there any apparent damage or problem with the gaskets or the sealing surface? | -- | Go to Step 19 | Go to Step 20
19 | Repair or replace the damaged components. Do the symptoms still exist? | -- | Go to Step 20 | System OK
20 | Measure the camshaft lobe lift. Is the camshaft within specifications? | -- | Go to Step 22 | Go to Step 21
21 | Replace the camshaft. Refer to Camshaft Replacement. Does the symptom still exist? | -- | Go to Step 22 | System OK
22 | If the problem is still suspected to be mechanical, remove the engine and perform a complete disassembly and inspection. Is the symptom repaired? | -- | System OK | Go to Base Engine Misfire Diagnosis