I keep popping the same code p0300 random missfire. I have ...

Cause

This condition may be due to high levels of internal corrosion in the distributor, causing misfire, rough idle, stall and Engine Cranks But Does Not Run. This corrosion is attributed to a lack of airflow internal to the cap caused by the vent screens being clogged with debris.

Correction

Remove the vent screens and inspect the internal components of the Distributor Ignition System using the procedure listed below. If the distributor base has to be replaced, the vent screens will also have to be removed on the new distributor. If there is evidence of this internal corrosion, replace the affected component. Refer to the appropriate procedure in the Engine Controls sub-section of the applicable Service Manual.

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Inspect the distributor cap. You may notice a white residue on the cap walls. For higher mileage occurrences, the interior of the cap may have changed to medium brown in color

Inspect the distributor rotor. You may notice the presence of black streaks on the plastic surface. More typical evidence would be visible green spots on the copper surface of the rotor segment.

Inspect the distributor base. You may notice high levels of surface rust on the distributor shaft or surface contamination on the sensor hold down screws.

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Inspect the distributor vent screens (1). If the vent screens are present, remove them by using a plastic-handled, long blade awl or pick (2). Insert into the airflow vent screens and pop them out. Refer to the figure for removal procedure. If the vent screens have been removed from the base of the distributor, then check the airflow inlets for being clogged with debris.

This is the other possibility.

DTC code P0300 or P0335.

Cause

The crankshaft sensor may be contacting the reluctor wheel.

Correction

Remove the crankshaft sensor. Refer to the Crankshaft Position Sensor Replacement procedure in the Engine Controls-4.3L sub-section of the Service Manual. After removing the sensor, inspect the end of it for witness marks that would indicate contact with the crankshaft. If contact with the reluctor ring is indicated, then inspect the front cover for cracking or other signs of alignment concerns. If the inspection indicates that the cover is causing mis-alignments, replace the cover. If replacing the cover, then the 0.5mm shim is not needed.

If the inspection of the front cover indicates that the cover is not the cause of mis-alignments, then the sensor should be shimmed. Add one shim between the sensor and the front cover. If the concern still exists, then add the second shim. Unless the sensor has been rubbed through the casing or deformed by contact with the crankshaft, it should not be replaced.

In either case, the crankshaft relearn procedure should be performed after any repairs.

Parts Information

Part Number

12565102

Description

Shim, 0.5mm thick

Qty 1-2

12562910

Sensor Crankshaft Position