For 1990-2009 cars

## Base Engine Misfire Diagnosis Table A

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Engine Performance diagnosis 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).

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 table will isolate any engine misfire due to a mechanical problem such as a faulty camshaft, leaking headgasket, etc. However, this table will not isolate a crossed injector wire, faulty injector, or any other component failure that may cause a misfire. Therefore, the On-Board Diagnostic System Check must be performed first in order to ensure the correct table is followed for diagnosis of a misfire. Refer to Engine Controls first, then, if necessary, refer to this table.

1 | Are there any obvious mechanical noises? | -- | Go to Base Engine Misfire Diagnosis | Go to Step 2
2 | Visually inspect the spark plugs, the wires, and the hoses for proper hook up or damage. Is there any damage 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 7 | Go to Step 10
6 |

1. Remove and inspect the intake manifold and the intake manifold gasket. Refer to Upper Intake Manifold Replacement or to Lower Intake Manifold Replacement .
2. Replace the parts as necessary.

Do the symptoms still exist?

--

Go to Step 11

System OK

7 | Remove and inspect the intake manifold and the intake manifold gasket. Refer to Upper Intake Manifold Replacement or to Lower Intake Manifold Replacement . Are the components damaged? | -- | Go to Step 8 | Go to Step 9
8 | Replace the parts as necessary Do the symptoms still exist? | -- | Go to Step 11 | System OK
9 | Remove and inspect the cylinder head. Refer to Cylinder Head Replacement . Refer to Cylinder Head Replacement . Are the valve guides or the seals damaged? | -- | Go to Step 8 | Go to Step 10
10 | Remove and inspect the piston, the piston rings, and the cylinder for wear. Refer to Connecting Rod, Bearing and Piston Replacement . Are the piston components damaged? | -- | Go to Step 8 | Go to Step 11
11 | Perform a cylinder leak test. Does the engine pass the cylinder leak test? | -- | Go to Step 12 | Go to Step 17
12 |

1. Install the spark plugs and a vacuum gauge to 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 14

Go to Step 13

13 | Inspect each vacuum operated accessory/vacuum line and repair any open or leaking components. Do the symptoms still exist? | -- | Go to Step 16 | System OK
14 | Using a spray bottle, lightly spray the spark plug wires and the distributor while listening to the engine. Did the engine stumble or fail? | -- | Go to Step15 | Go to Step 16
15 | Replace the spark plug wires and/or the distributor cap and the rotor. Do the symptoms still exist? | -- | Go to Step 16 | System OK
16 | Remove the intake manifold and carefully inspect the intake manifold gasket and the TBI gasket. Refer to Upper Intake Manifold Replacement . Refer to Lower Intake Manifold Replacement . Is there any apparent damage or problem with the gaskets or the sealing surface? | -- | Go to Step 17 | Go to Step 18
17 | Repair or replace the damaged components. Do the symptoms still exist? | -- | Go to Step 18 | System OK
18 | With the intake manifold removed, rotate the engine and measure the camshaft lobe lift. Is the camshaft within specifications? | -- | Go to Step 20 | Go to Step 19
19 | Replace the camshaft. Refer to Camshaft Removal . Refer to Camshaft Installation . Does the symptom still exist? | -- | Go to Step 20 | System OK
20 | 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

## Base Engine Misfire Diagnosis Table B

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Engine Performance diagnosis 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 (MF1).

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 table will isolate any engine misfire due to a mechanical problem such as a faulty camshaft, leaking headgasket, etc. However, this table will not isolate a crossed injector wire, faulty injector, or any other component failure that may cause a misfire. Therefore, the On-Board Diagnostic System Check must be performed first, in order to ensure the correct table is followed for diagnosis of a misfire. Refer to Engine Controls first, then, if necessary, refer to this table.

1 |

1. With the engine running, try to determine if the noise is timed to the crankshaft speed or the camshaft speed.
2. Using a timing light, two knocks per flash is the crankshaft or one knock per flash is the camshaft.

Is the noise timed to the crankshaft speed?

--

Go to Step 2

Go to Step 3

2 |

1. Remove the rod bearings and inspect the bearings and the journals for wear.
2. If the parts are OK, remove the crankshaft and inspect the main bearing and journals for wear.
3. Replace the parts as necessary.

Does the engine continue to misfire?

--

Go to Step 3

System OK

3 | Check to see if the noise is timed to the camshaft speed. Is the noise timed to the camshaft speed? | -- | Go to Step 5 | Go to Step 4
4 |

1. Inspect for loose accessory attachments, the flywheel, or the torque converter.
2. Tighten or adjust as necessary.

Does the engine continue to misfire?

--

Go to Step 5

System OK

5 |

1. Remove the intake manifold. Refer to Upper Intake Manifold Replacement or to Lower Intake Manifold Replacement .

Refer to Camshaft Removal .

2. Rotate the engine and measure the lifter movement in the bore.
3. Compare the measurement with the specifications in Engine Mechanical Specifications .

Is the camshaft within specifications?

--

Go to Step 7

Go to Step 6

6 | Replace the camshaft. Refer to Camshaft Removal and Camshaft Installation . Does the engine continue to misfire? | -- | Go to Step 7 | System OK
7 |

1. Remove the rocker arms, the pushrods, and the lifters.
2. Inspect the parts for excessive wear or damage.
3. Replace the parts as necessary.

Are the repairs complete?

--

System OK

--