On this 83' 240, I have tried to get the spark plug wires off to check the plugs. The plug shroud seems to completely cover the plugs and I have tried to pull them off by grabbing the whole shrould and even with easy to moderate force. They don't budge. Is there a twist that goes with the pull or some other secret incantation (PG) that is done to remove the wires? I always get great advice here and as impatient as I am to check the plugs I decided to see what advice I can get instead of regretting a hasty action.. Thanks Rojo.