Engine light on throwing codes p300 and 306

Hi,

The idea that the misfire is specific to cylinder 6 and the vehicle has a lot of miles on it, there is a chance that the engine compression is lower in that one cylinder. To check would require doing an engine compression test. Here is a link that shows how that is done:

https://www.2carpros.com/articles/how-to-test-engine-compression

Here are the directions specific to your vehicle:

2006 Buick LaCrosse V6-3.8L VIN 2
Component Tests and General Diagnostics
Vehicle Powertrain Management Tune-up and Engine Performance Checks Compression Check Testing and Inspection Component Tests and General Diagnostics
COMPONENT TESTS AND GENERAL DIAGNOSTICS
Engine Compression Test

Tools Required
J38722 Compression Tester

A compression pressure test of the engine cylinders determines the condition of the rings, the valves, and the head gasket.
1. Run the engine until it reaches normal operating temperature. The battery must be at or near full charge.
2. Turn the engine OFF.

3. Disable the ignition.

Important: Remove the Powertrain Control Module (PCM) and the ignition fuses from the I/P fuse block.

4. Disable the fuel systems.
5. Remove the spark plugs from all the cylinders.
6. Remove the air duct from the throttle body.
7. Block the throttle plate in the open position.

pic 1

8. Measure the engine compression, using the following procedure:
1. Firmly install J38722 to the spark plug hole.
2. Have an assistant crank the engine through at least four compression strokes in the testing cylinder.
3. Check and record the readings on J38722 at each stroke.
4. Disconnect J38722.
5. Repeat the compression test for each cylinder.

9. Record the compression readings from all of the cylinders.
The lowest reading should not be less than 70 percent of the highest reading.
No cylinder reading should be less than 689 kPa (100 psi).

10. The following are examples of the possible measurements:
When the compression measurement is normal, the compression builds up quickly and evenly to the specified compression on each cylinder.
When the compression is low on the first stroke and tends to build up on the following strokes, but does not reach the normal compression, or if the compression improves considerably with the addition of three squirts of oil, the piston rings may be the cause.
When the compression is low on the first stroke and does not build up in the following strokes, or the addition of oil does not affect the compression, the valves may be the cause.
When the compression is low on two adjacent cylinders, or coolant is present in the crankcase, the head gasket may be the cause.

11. Remove the block from the throttle plate.
12. Install the air duct to the throttle body.
13. Install the spark plugs.
14. Install the Powertrain Control Module (PCM) fuse.
15. Install the ignition fuse to the I/P fuse block.

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One other thought is there could be an issue with the number 6 fuel injector. You may want to switch it with an injector from a different cylinder to see if the misfire moves cylinders.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Let me know.
Joe

LOL, I got you. Yes, the crank needs to be tight. If there is any play it can cause play.

Try switching the injector with a different cylinder to see if the misfire changes. Also, the auto-correct has given me issues as well. LOL No problem. I figured it out.

Take care and let me know what you find or if I can help.

Joe