#5 cylinder misfire.changed coil packs out and it's still reading misfire.burning alot of gas.I don't know what the problem is.tried just about all I know.

SOURCE: 2003 Chevy Venture misfiring

The injector is a good possibility, although you should check for spark in the wire first, as the electrical is the weakest link in the system. Put a spare plug in the end of the wire with the plug resting on metal, then have someone crank the van to see if you have spark that far, test and replace spark plug, (do not get shocked!) then look into a new injector or a good cleaning.

SOURCE: po 300 code pops up random cylinder misfire and

get a new car

SOURCE: I have a 2002 TrailBlazer with the straight

did you replace only one spark plug? that can cause issues because of differences in resistances between cylinders. also, did the map code stay off after replacing
?

SOURCE: code p0300

If you already replaced the wires, I would suggest replacing the plugs, distributor cap and rotor. They are also very important parts of the spark. Fuel injector problems can also cause misfires.

SOURCE: misfire #1 cylinder (autozone scanner) I changed

inspect the sparkplug plug first!! After engine is running for 20 sec (while misfiring), pull your #1 sparkplug and check for fuel. If there is no fuel replace the injector!!If there is fuel, post a comment for more help!!