Intermittent Lack of Power and/or DTC P0326

Some customers may comment about an intermittent lack of power on acceleration on vehicles equipped with SOHC (L24) engines. This condition is most likely to occur on a vehicle which has had a cylinder head replacement.

This condition may be caused by the knock sensor picking up noises within a certain frequency and during specific engine conditions that the PCM may incorrectly interpret as spark knock. The PCM will retard spark advance in an attempt to eliminate the perceived spark knock. If this reduction in spark advance is great enough, the driver will perceive a loss of power from the vehicle.

This condition can result from several different causes, however the two primary causes addressed by this bulletin are:

Refer to the procedure in this bulletin for corrective action.

1. Evaluate vehicle under the conditions described by the customer. This condition may be very intermittent and difficult to reproduce. This condition is most likely to occur with the engine at normal operating temperature, under light to moderate load, under light to moderate throttle, and engine speed between 1500--2000 rpm.
2. Using a Scan tool, monitor the following parameters in the SPARK CONTROL screen under the Engine Data Display:

•	LOW SPARK MODIFIER

•	MID SPARK MODIFIER

•	HIGH SPARK MODIFIER

•	If any or all of the SPARK MODIFIERS increase above 6.0 and the lack of power is experienced process to next step.

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If none of the SPARK MODIFIERS shown any activity but the values stay in lower (below 4.0) range and are intermittent, the condition may not be corrected by the parts and procedures in this bulletin. Refer to additional diagnostic information (Low Refer to additional diagnostic information (Low Power, Spark Knock, or DTC P0326) in the appropriate model year Powertrain Controls service manual.




3. Camshaft identification number must be located and read.
4. Remove cylinder head rocker cover. (Refer to "SOHC (L24) Cylinder Head Removal" procedure in the appropriate model year Engine/Fuel/Air Intake/Exhaust service manual for rocker cover removal information.)
5. Remove the rear camshaft bearing plug by tapping it inward (toward the camshaft) using a punch and a hammer. Remove the plug from the cylinder head and discard.



6. Inspect the end of the camshaft for stamped identification numbers. The identification numbers may be difficult to see. Use various light angles and/or a magnifying glass to aid viewing if you are unable to distinguish the ID numbers easily.

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If the four digits "7289" are not stamped into the end of the camshaft, the date code is before June 1, 1998 (A/B/C 6018), or the numbers cannot be determined, obtain and install a new camshaft P/N 21007289 and proceed to next step. (refer to "Camshaft - In - Vehicle" procedure in the SOHC Cylinder Head section of the appropriate model year Engine/Fuel/Air Intake/Exhaust service manual.

•	If the four digits "7289" (last four digits of P/N 21007289) are stamped into the end of the camshaft and/or the heat treat date is on or after June 1, 1998 (A/B/C 6018) proceed to next step.

7. Coat a new rear camshaft bearing plug P/N 21006560 with Saturn P/N 21485277. (Loctite 242 ® or equivalent) and install it using an approximately sized standard bushing driver.
8. Install cylinder head rocker cover. (Refer to the "SOHC (L24) Cylinder Head Installation" procedure in the SOHC (L24) Cylinder Head section of the appropriate model year Engine/Fuel/Air Intake/Exhaust service manual for rocker cover installation information.)
9. Install new knock sensor (P/N 21025126). (Refer to "Knock Sensor" procedure in the Ignition/Spark Control section of the appropriate model year Powertrain Controls service manual for knock sensor procedure.)

Important: The Loctite 242® must be claimed as a "material" using Net Item Code "M." Refer to the table below for the material required, material cost, quantity required, and material reimbursement amount.