Po304 Code – Misfire No. 4 Cylinder….?

I have a ’99 Ford Ranger 4.0L with about 159K miles on it. Recently I started experiencing rough idle and the car occasionally surging past 40 MPH. The Check Engine Light finally came on and my OBDII indicated a P0304 Code (#4 Cylinder Misfire). I proceeded to check the usual suspects commencing with the plug, ignition wire, coil pack and wiring to PCM. Since it only affected a single cylinder, I discounted the PCM, and the coil pack, and visually I couldn’t find anything wrong with the ignition wire nor the plug. But lo and behold, when I swapped the #4 plug with the #5 plug, #5 cylinder started to misfire thus the culprit was the plug. Physically I couldn’t detect anything wrong with the plug (Iridium, 30K miles old), no cracks, no build up, no shorts, electrode looks good, etc. Something internally must be breaking down but what? Any ideas? BTW, after I replaced the plug, I got the problem solved.

Both comments and pings are currently closed.

2 Responses to “Po304 Code – Misfire No. 4 Cylinder….?”

  1. buddy_23 says:

    I run into this all of the time, at some point the plug was probably dropped and the ceramic insulation under the casing of the plug got cracked, electricity finds the path of least resistance to ground (conventionally speaking) so even though the gap of the plug might be .050 this gap lives in very a harsh environment so it would be a lot easier for the spark to jump the larger gap in a a more conductive environment up in the core of the spark plug.

  2. Mouseket says:

    In most case its best to use the recommended spark plugs for the vehicle. Using the wrong grade plug could (overtime) breakdown the coil and the plug wires. My guess your truck should take Motorcraft platinum plugs. If you have your owners manual or repair manual these references should confirm this. Note, It is good practice to replace the spark plug wires with a good quality set at the same time as the plugs as they could be the original ones for ’99.

Powered by WordPress | Designed by: free css template | Thanks to hostgator coupon and web hosting reviews