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.

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. 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

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

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

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

1. Remove the intake manifold. Refer to Intake Manifold Replacement .
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

Replace the camshaft. Refer to Camshaft Replacement .

Does the engine continue to misfire?

--

Go to Step 7

System OK

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

--

Engine performance diagnosis procedures are covered in Engine Controls and should be consulted for diagnosis of any Driveability, Emissions, or Malfunctioning Indicator Lamp (MIL) concerns.

The following diagnosis covers common concerns and possible causes.

When the proper diagnosis is made, the concern should be corrected by adjustment, repair or replacement as required.

Refer to the appropriate section of the service manual for each specific procedure.

This diagnostic table will assist in engine misfire diagnosis due to a mechanical concern such as a faulty camshaft, worn or damaged bearings.

a crossed injector wire, faulty injector or any other driveability component failure that may cause a misfire.

The Powertrain On-Board Diagnostic System checks must be performed first.

When using this table to make a Base Engine Misfire diagnosis, begin with the preliminary information below and then proceed to the specific category.

Preliminary

1. Perform DTC P0300 before proceeding with Base Engine Misfire Diagnosis information.

DTC P0300 will assist in determining which cylinder or cylinders are misfiring.

2. Perform a visual inspection of the following:

•	Loose or improperly installed engine flywheel or crankshaft balancer

•	Worn, damaged, or misaligned accessory drive system components

3. Listen to the engine for any abnormal internal engine noises.
4. Verify the engine has acceptable oil pressure.

Refer to Low or No Oil Pressure .

5. Verify if the engine has excessive oil consumption.

Refer to Excessive Oil Loss .

6. Verify if the engine has coolant consumption.
7. Perform a compression test on the engine.

Refer to Engine Compression Test .

Intake Manifold Leaks

An intake manifold that has a vacuum leak may cause a misfire.

Inspect for the following:

Coolant Consumption

Coolant consumption may or may not cause the engine to overheat.

Inspect for the following:

Oil Consumption

1. Oil consumption may or may not cause the engine to misfire.
2. Remove the spark plugs and inspect for an oil fouled spark plug.
3. Perform a cylinder compression test.

Refer to Engine Compression Test .

4. If the compression test indicates worn valves or valve guides, inspect for the following:

•	Worn valve guides

•	Worn valve stems

•	Worn or burnt valves or valve seats

•	Worn, brittle, or improperly installed valve stem oil seals

5. If the compression test indicates worn or damaged piston rings, inspect the following:

•	Broken, missing, misinstalled or improperly seated piston rings

•	Excessive piston ring end gap

•	Excessive cylinder bore wear or taper

•	Cylinder damage

•	Piston damage

Abnormal Internal Engine Noises

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

•	Missing or loose valve train components

•	Faulty valve lifters

•	Faulty valve springs

•	Bent or burnt valves

•	Worn camshaft lobes

•	Worn or damaged timing chain and/or sprockets

Important: A slight COLD knock or piston slapping noise could be considered normal if not present after the engine has reached normal operating temperatures.

4. If the knock is timed to crankshaft speed, inspect the following:

•	Worn crankshaft main or connecting rod bearings

•	Piston or cylinder damage

•	Worn piston or piston pin

•	Damaged or faulty connecting rod

•	Excessive carbon build-up on the top of the piston

No Abnormal Internal Engine Noise

1. Remove the camshaft cover on the side of the engine with the cylinder that is misfiring.
2. Inspect for the following:

•	Worn or improperly installed timing chain and/or sprockets.

•	Faulty valve springs

•	Worn valve lifters on the camshaft or valve tip surfaces.

•	Faulty valve lifters (bleeding down)

•	Worn or improperly seated valves

•	Worn camshaft lobes