440 misfire gremlin.

[P Dubya]

I'm chasing a misfire on a 440. Pretty sure I have it pinpointed to rear most cylinder on passenger side. So far what I have done is....
Checked under cap. No arcing and looks pretty good in there.
Ohm'd wires. They ran between 5K for the shortest wire up to about 11K for the longest wire.

Pulled plugs and found one fouled. (Rear/passeger) Replaced that plug with a better but not new plug as I didnt have any on hand. Started it up after the plug swap and thought all would be good. Now the misfire has changed sounds from a subtle misfire to a full on backfire out the tailpipe. Any ideas on what to look into next? Cam lobe going flat? Sticking valve? I'm pretty frustrated....

 

[AR67GTX]

If you have another old plug wire that will fit I would try changing it out and see if it changes any. Sometimes a wire will ohm OK but the inner filament is damaged and shorts out with engine vibration - usually at one of the terminals.

 

[khryslerkid]

I had a fouled plug like that this year. Moving the car too many times without letting it warm up. Used my IR gun and determined which cylinder it was. Removed the plug, cleaned it, reinstalled and alls well. Go figure.

 

[PurpleBeeper]

the plug on the right looks oil fouled, so maybe a bad valve seal on that one cylinder? Maybe try one of those anti-foul things that screws over the electrode tip

 

[Geoff 2]

Should be a 12 heat range for a Champion & 5 heat range for NGK.

Measuring wire resistance is not 100% definitive of a problem. Try some other wires or swap wires to see if problem moves with the wire.

 

[kiwigtx]

I'm chasing a misfire on a 440. Pretty sure I have it pinpointed to rear most cylinder on passenger side. So far what I have done is....
Checked under cap. No arcing and looks pretty good in there.
Ohm'd wires. They ran between 5K for the shortest wire up to about 11K for the longest wire. View attachment 1516435
Pulled plugs and found one fouled. (Rear/passeger) Replaced that plug with a better but not new plug as I didnt have any on hand. Started it up after the plug swap and thought all would be good. Now the misfire has changed sounds from a subtle misfire to a full on backfire out the tailpipe. Any ideas on what to look into next? Cam lobe going flat? Sticking valve? I'm pretty frustrated....

Replace the condenser. I had one go bad and it killed the ignition.

Possibly the cheapest part of the system also.

 

[khryslerkid]

Replace the condenser. I had one go bad and it killed the ignition.

Possibly the cheapest part of the system also.

Bad condenser can act like that.

Reading the title of the thread I thought someone put a 440 in a AMC

 

[P Dubya]

Well... Pretty sure i have a burned valve. This is all the cylinder in question will make....

 

[Orig69]

Before removing the valve cover I would put a teaspoon of oil in the spark plug hole and do another compression test.