My car has just rolled over 100k, and has developed a misfire on Cylinder 5 (and 4 and 6 if you believe the diagnostic) which returns after reset.

Would you just bite the bullet and replace all plugs and coils?

Depends how much they cost and how long you want to keep it. Ford wanted more for a single lead for the OH’s Fiesta than it cost for an entire set + coil on my car!

In the end it turned out it was just the coil.

A full (6 of each) set of Bosch parts will be £220. I can fit them myself. I’m keeping the car for as long as it lasts.

have a search on ebay and eurocarparts for the coil (s) – massive differences in pricing. I was just able to do the coil/4 plugs in my poxy vauxhall for £35 – coil was 2nd hand but a new branded one was only £60

A full (6 of each) set of Bosch parts will be £220. I can fit them myself. I’m keeping the car for as long as it lasts.

Yes, but is that likley to be another 100k (in which case replace like for like), or limping on for another year or two (get a set from a scrap car).

If it were me I’d replace the coil and see if that cures it. I know they’re supposed to outlast the leads, but it always seems to be the coil that goes when it’s my car.

[edit: and this assumes it’s the coil or lead that’s failed]

On motorcycles with individual coils for each spark plug lead and revving to 14,000rpm a misfire is annoying, but it can be as simple as spark plugs. It’s worth having a look at the spark plugs and or throwing in a new set.

Actually, having scratched my head a bit last night.

My car has just rolled over 100k, and has developed a misfire on Cylinder 5 (and 4 and 6 if you believe the diagnostic) which returns after reset.

Are you sure it’s not 4 and 6 (or 4+5, or 5+6 depending on firing order)?

Wasted spark ignition would give a missfire on two cylinders with a single coil failure. HT lead failure would give a missfire on one cylinder.

Although having typed that out I’m not so sure. If one HT lead failed, would that impact on the other cylinder on the same coil? Do V6’s have a tripple wasted spark rather than pairs? Is it a single coil with a distributor or a coil pack?

Buy the set and replace as they go ?

Swap the coil to another cylinder and see if the missfre follows it.