my truck is a 1997 nissan pickup with. 254,000 miles.check engine light come on.only when i’am at highway speed.as long as i’am in city traffic, nothing i have a code scanner code(p.o.302) number 2 cylinder misfiring. i change spark plugs and wires .and dist cap.but check engine light came back on.i put in shop they claim that they can’t find nothing wrong.i guess i need to find a new mechanic.
presume you changed the ignition rotor also. “misfire” means the crank isn’t measured as turning as fast as it should after the cylinder fires. It could be a spark problem, but it looks like you’ve done a lot to eliminate that as a possibility and the problem still remains. I guess it could be a problem in the spark generation electronics, but that seems unlikely. So what else? … well, it could be a fuel problem, like a faulty injector in number 2. Another idea is that there is really nothing wrong, but the ECM thinks the crank isn’t turning at the correct speed after number 2 fires b/c the component which measures the crank speed is faulty. That’s usually the crank position sensor, but sometimes – esp in early 90’s cars – there is a component inside the distributor that is involved.
How about a compression test? Has that been done?