Engine Performance problem
1998 Other Plymouth Models 4 cyl Front Wheel Drive Automatic 113000 miles
This is a 1998 Plymouth Neon which blew a headgasket. We had the head ground and installed a new head gasket, along with numerous other things like starter, plug & plug wires, oil & filters, etc. And the car runs and idels like a top. When we put the OBD II meter on it, it comes back with Codes 300-304, which says " Engine Misfire". We took it to get the Texas State Inspection sticker(This car was last registered in California.) And their machine shows: Catalyst-Not Ready, Evap-Not Ready and EGR-Not Ready. Eventhough the exaust test passes they cannot give a sticker until those codes are clear from the computer. Those codes do not show up on our OBD II. After connecting the battery up yesterday, we drove it about 40 miles before attempting to get it inspected and the codes showed up in their machine. Do you have any suggestions on what we can do about these codes?
P0300 is a Random Misfire/ P0301-P0304 specific cylinder misfire
Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.
A Random Misfire code usually indicates a vacuum leak or bad gas.
A misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression.