PO300 Random Mifire Solved (for me) - Distributor Related
 

I picked up a beautiful 1998 Blazer 4Door 4WD this year with only 90,000 miles. I figured I could fix anything mechanical as the body, frame, and interior were like new (California car... garaged for much of it's life).

I immediately had to solve the random engine misfire problem that is so prevalent on this forum. My problem was very apparent when the engine was cold from sitting overnight and cleared up as the engine warmed up. At full operating temperature (after 30 minutes of driving) there was not apparent misfire at all.

I tried many of the solutions that others have posted and none worked for me... but, thank you to all that have posted as I have learned a lot about the engine as a result.

My local Firestone Dealer could not figure out the PO300 problem through their electronic diagnostics... which surprised me - excellent shop that has done a lot of other work; brakes, oil cooler lines, tires. Their lead mechanic directed me to the best GM dealer in my area. I dropped the car off at the GM Dealer and they diagnosed and fixed the problem as distributor related. The distributor had slipped/advanced to 20 degrees advancement and this was not apparent in the Firestone diagnostic.

Anyway... I was going to replace the fuel injection spider and found the problem to be a distributor adjustment. The Blazer runs great now cold or hot... just wanted to pass this on to other 1998 Blazer owners that may still be having cold engine misfire.