Why does a Vortec Engine misfire?
Obviously, if it is tune up time, worn out plugs or wires will cause a misfire. The factory installed plugs and wires will usually go about 100,000 miles, although I have seen 120,000 fairly often. This is a great thing because the vehicle needs double platinum or iridium spark plugs which can get expensive. We don’t want to change these too often. If a tuneup has been done fairly recently AND the proper plugs and wires were used AND the person doing the tune up didn’t crack a porcelain on the plug or damage the wire in some way, we probably need to look elsewhere for our misfire. This is where a scan tool of some sort will be vital. A scan tool with a data stream will usually indicate which cylinder is misfiring. Occasional the trouble code reported will indicate the cylinder. P0301, for instance, indicates cylinder # 1 is the culprit. P0304 means number 4, etc. P0300 is a bear because it means Random Cylinder Misfire. In other words, there isn’t enough variation in crankshaft speed f
