Computer keeps throwing a code for a random misfire and a misfire on the first cylinder, i have replaced the coil pack on the first cylinder and swapped all the spark plugs and it still throws this code, any ideas?

 

Keep testing. Misfire is likely on another cylinder

 

Clogged or 'dribbly' fuel injector??

Misfire does Not have to be spark.

bob

 

Bad tank of gas that becomes critical at idle ?

TECHRON is a recommended fuel injector cleaner that is an easy try for a possible lagging or dragging fuel injector position

Intake or exhaust manifold leak causing problems at idle ?

Does the butterfly return to the mechanical idle stop ? You can twist the tower bellcrank by hand . Gummy and binding throttle body preventing butterfly from returnig to the idle stop

Weak return spring covered by TSB and a higher prelaoding of the original return spring that some people have done

The missing cylinder CEL comes from the 2 knock sensors and how well they can discern if its cylinder 1 , 2 , 3 , 4 , 5 , or 6 ( I can be wrong )

Not a easy job for a first generation ECU with OBD 2

 

Hi Hugemungus,

Another common issue on the X300 is the insulation on the wires to the coils, which becomes brittle and cracks and sometimes just falls off of the wires, allowing shorts that lead to misfires. A very common point of failure is in the bend in the harness at the rear end of the cylinder head. You have to unwrap the harness to inspect all the wires in that area.

When you replaced the spark plugs did you notice any oil in the spark plug wells? Oil from leaking plug well seals can seep down the spark plug threads and interrupt the ground path for spark.

As xalty and Parker have alluded, the X300 OBD system is not particularly good at identifying which cylinder is misfiring. I once chased a P0303 (cylinder 3 misfire) code for a long time, only to eventually discover the misfire was actually in cylinder 6.

If none of the checks that have been mentioned reveal the problem, you may need to do a compression test to rule out a problem with a valve, rings, etc.

Cheers,

Don