Poor Engine Performance-Misfire, Rough Idle, Stalls, Engine Cranks but Does Not Run, SES/Check Engine Light On, DTC P0300 Set (Inspect Distributor Ignition(DI) System Components, Replace as Necessary)

Some customers may comment on poor engine performance and the Service Engine Soon/Check Engine light being illuminated. Upon investigation, the technician may find DTC P0300 set.

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.

Important: It has been determined on the Sierra and Silverado applications with the 4.3L engine that the A/C accumulator line is routed directly above the distributor area and condensation from that line can aggravate the corrosion condition. For these vehicles, install the foam sleeve, P/N 15190971, to the A/C line. Cut a slit in the sleeve and secure to the line using tie-straps.

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.

Important: All of these inspections can be done on-vehicle.

1. 1. 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.
2. 2. 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.
3. 3. 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.



4. 4. 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.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: