: Misfiring and Service Engine light

08-06-04, 10:19 AM
This is my first northstar Cadillac. It has 73,000 miles. On city streets it is fine and the SES light even turns off after a couple of days. This is the third time the light turned on. I did the plugs, PCV, air filter, fuel filter, about 3 months ago. I changed the fuel regulator about 1 month ago because I was having starting problems, but it is fine now. When I drive on the highway is when the SES light turns on, if anyone has any suggestions, much appreciated.

Thank you


08-29-04, 08:38 PM
check the egr valve

08-29-04, 11:09 PM
If the SES light is coming on, you should be getting a code. Have you checked for one?


08-31-04, 07:28 AM
I received the P0300 code from the OBD in the car. Then I went to AutoZone and it came up with P0307. I am going to change the Plug wires and see what happens.

Thank you,


08-31-04, 07:49 AM
. P0300 - Engine Misfire Detected
. P0307 - Cylinder 7 Misfire Detected

Pull off plug wire and look in spark plug tube for water.
Remove a few plugs to see condition, should be nearly white in color.
Plugs should be DUAL platinum; check to be sure both pads are in place.
Check to be sure all of the plug wires are on tight.

At 70k you may want to go ahead and replace the spark plugs, if so use DUAL platinum type.