I have a P303 code indicating a misfire on cylinder 3. Coincidently I recently changed the spark plugs, so I will check out the one in cylinder 3. However I don't know which cylinder is number 3. Anyone know? Thanks.

 

No.1 cylinder is the front of the engine, which would be the passenger side of the car. The rest just go in order: 1,2,3,4.

 

X2 and you can swap plugs and coils into different cyl. To see if the misfire moves for help in diagnostics.

 

Thanks.

 

If you recently changed your plugs then your mileage is probably getting up around the point where Ecotec's throw the misfire code...there are a lot of threads on the subject and it often indicates you have a burnt valve (in this case in Cyl 3) which requires the cylinder head to be removed, valve job and new valve or valves in Cyl 3, costing $1000-1500 depending on what parts you change.

The ONLY way to check for a burnt valve is a simple compression check. You can buy a compression guage cheaper than garages will charge you for the test. I got 180 psi in 3 cylinders and 90 psi in the one with the burnt valve. Drove with CEL on for 30,000kms, then the idle got rough, then I checked compression and finally had to bite the bullet and take it to the machine shop...now it runs perfect!