I own a 2003 LR Discover 2. Had misfires on cylinders 4, 6, and 8. Replaced spark plugs on 4 and 6. Noticed the wire on 8 was loose so fixed that. Cleared codes and now only misfire on 4. Bad wire on 4?

 

Plug, wire, coil, ECM. Maybe swap the 4 wire to another cylinder to see if the fault follows it.

 

Thanks. I'll try that. Is the ECM the truck's computer?

 

Yes, ECM = Engine Control Module = computer. That is the last thing to check. Test the easy stuff first. ECM sends a pulse to the coil, coil produces high volts to the wire, wire transmits high volts to the plug, plug has the correct gap to produce the spark, all at the right time. If the miss follows the wire, then the wire is bad. If it does not follow the wire, then maybe try a new plug, or swap the plug to a different cylinder. Try one change at a time to pinpoint the faulty component.

 

Do you know the range of spark plug gaps thet you can use for LR Disc 2?

 

I think spec is 0.035 - 0.041 inch. Might be printed on a label under the hood. Some folks use 0.040 (1mm) others use 0.044 (1.1mm). Some go up to 0.050 inch (1.25mm). Best to get them all nearly equal.

 

Ok. Since cylinder 4 is missfiring and shares a coil pack with cylinder 3 that is not missfiring, cylinder 4 may have a bad wire or plug. As discussed, I have already replaced the plug so it must be the wire?

 

Likely, but I think it’s also possible that the coil has an internal fault.

 

Start methodically swapping known good with suspected bad. Swap number four wire with number three wire, then swap coils left to right,

 

To clarify, the wasted spark for 4 is cylinder 7 (not 3). Firing order 1-8-4-3-6-5-7-2. 4 and 3 are not on the same coil. Swapping the parts should cause the fault to follow, so that is more definite than trying new parts because a new part is not proven to be good yet, vs the part swapped in to the bad position. Hope this helps.