I have a 1996 xj600 Yamaha. I 've been experiencing a engine miss fire. I checked for spark by pulling each plug and grounding them out on the block. Number 4 doesn't spark at all, so I replaced the plugs and it still has the same problem. Could this be a bad plug wire or coil or CDI unit ?

Check the engine block ground strap or ground wire. Does the plug fire when held close to the block?

Check your tank vent. Ride the bike until it stalls, pull over and pop open the gas tank lid. If you hear a "ffffwwwwwah" of air being sucked in when you open the tank, your air vent is blocked. The bike runs great when you start out, but as fuel is taken out of the tank no air can get in to replace it and the tank develops a vacuum.

Spark plug or coil likely problem. Might put a spark plug in the #3 wire and crank it over and see if it sparks. Plug will need to be grounded and someone to watch or crank engine for you. Leave original plug in hole while doing this. If you have a timing light. Attach it to the wire with it plugged to the original spark plug and start engine. If the light flashes the the coil and wire has power. If no light then more likely a coil. Depends on year of auto as well. Most of the newer ones have a coil for each plug. If its a older one... likely a plug or plug wire.

Remove the spark plug and flush out the excessive OVERFLOW OF FUEL as the engine failed to start. Unless this is flushed out the overflow of fuel with the dampness will not fire the cylinder.
Also check on the spark intensity with the plug as it must be good.
If not check the HT coils and the HT wires, check the incicent voltage on the HT coils for the coil trigger which must be fluctuating 12 volts.
This must start the engine if the timing is correct.

This is a quick explanation:

1996 Dodge Caravan
3.3 liter




The big rectangles are referencing the engine, the cylinder associated to it's "firing" are the colored circles, and the are also the location of the spark plugs....the smaller lego-looking block is your coil pack. The spark plug wires run from the coil pack to the spark plug on the engine. The wires match 1 to1 or black to black...and so on....

When these are matched to each cylinder/spark plug and it's wire leading to the matching coil pack position, this is it's "firing order". If one of the wires is "crossed" meaning, not 1 going to 1, then the engine will "miss-fire".

did you check wire and spark plugs you could have a miss fire is your check engine on and the codes p0300 301 302 303 304 if you want remove the wires from plugs one at a time leave them loose and start engine then watch not to get a shock pull up on one at a time the spark plug wires and see if the fire jumps

do 2 things charge your battery. see if it stays the same on the spark . sounds like coil breakdown . change if needed.

Matter not whether plug fires out of engine. Put it back in and clamp a timing ligh to it. If the light won't fire, you don't have enough spark to fire cylinder, hense miss.