Diagnostic trouble code P0305 in your 2001 Ford Ranger tells you that the misfire detection monitor identified a misfire condition in cylinder No. 5. If the misfire is severe enough to damage the catalytic converter, the "Check Engine" light will blink in one-second intervals.
If other codes are present -- such as P0136, P0156, P0171, P0172, P0175, P1130 or P1150 -- the P0305 may be a symptom and not the cause of your problem. Pursue other codes to find the source of the problem. If your Ranger isn't exhibiting any performance problems, reset the DTC, using a scan tool or by disconnecting the negative battery cable, and see if the code returns.
To diagnose a P0305, look for problems that would cause a lack of combustion in cylinder No. 5. To achieve combustion, you need compression, spark, fuel and air -- all precisely timed and metered. Look at fuel pressure and fuel metering for that cylinder as well as no spark, low or no compression, or air leaks. Swap plugs and wires between cylinder No. 5 and another cylinder to see if the DTC changes.
