Thread: V8 intermittent Misfire

Hi all,

Chasing an intermittent misfire on cylinder #4, not sure what to try next.

I replaced all plugs, wires and both coil packs about 12 months ago, I had trouble free motoring with pretty good fuel economy until this summer.
On a hot day (well hot for New Zealand) having already driven into town I had a very lumpy idle upon starting, checking the plug leads found #4 and #8 slightly loose on the spark plugs, and #5 so loose I had to squeeze the connector together with my pliers to get a good contact.

The vehicle ran pretty well for a few months after that but recently started misfiring under load, sometimes I just notice a little loss of power but other times had quite a violent shudder that goes through the whole vehicle.
Checking the codes showed misfires logged for cylinders 3, 4, 5 and 8, but checking live data the misfires seem to only be on cylinder #4.
I put this down to the loose leads so ordered a new set of leads, checking the spark plugs some were a little fouled but nothing too major and nothing wet.
I installed the new leads yesterday, haven't done much driving but the live data still shows intermittent misfires on #4, always when driving.
I've pulled the spark plug again and it looked pretty black, I tried switching the plugs on cylinder #2 and #4 to see if it moved the misfire, but it's still showing #4 missing.


I'm getting good fuel consumption, not using water or oil, running well when not misfiring, the Oxy sensors are working as they are supposed too.
Should I be replacing the coil packs? Or trying something else.
I feel that it is an ignition problems as one would expect a fuel or air problem too effect more than the one cylinder and to happen less intermittently.

Any help would be greatly appreciated.
Cheers.

Did you replace the leads with oem ones, apparently these engines should keep the stock leads

i would start looking at the coil packs, but they are a pain to get at.