Thread: V8 Missfire on Cylinder 5

Have you removed the plug on no.5 and swapped it with another? Sometimes plugs are damaged or faulty. Check its colour.

You have maybe damaged or loosened a plug lead. Check the plug function by fitting a spare plug to no.5 lead and earthing the plug body with a suitable earthing lead, eg a jumper lead.

The plug leads are entirely different to the 3.9, which has a distributor at the front of the engine with traditional hollow posts on the cap. You need the correct leads (and high levels of manual dexterity) for replacement.

I replaced the HT lead no change. I swapped the plug on Cyl 3 and 5 (while I was checking compression on the left bank) now the miss-fire is worse than at the beginning. Plug also burning a bit more black

I did a compression test all the cylinders are pushing similar values, so no gas escaping.

That leaves the coil pack. The top bracket was bent up, and not holding the pack in place, it only rests on the bottom bracket. Could this influence the earth on a single cylinder? AFAIK if the coil is dodgy both 5 and 8 will miss.

Other than that I guess it is an injector?

Originally Posted by ob1

(we have open loop systems in SA)

South Australia (SA), South Aftica (RSA or ZA), or Saudi Arabia (KSA)?

Any chance it is a coolant leak into the cylinder?