diagnose valve problem?

[KJM]

my 165 l6 is idling a bit rough, seems to be missing a bit, when reving up too. she was idling and running great until the other evening i was heading out fishing and all was well until she suddenly started missing. long story short, i found the plug wire for cylinder #6 had come off the distributer and was hanging loose. easy fix, except she now still has a miss. i ran her about an hour on 5 cylinders the day it happened.....could this cause any damage. tonight while she idled in my driveway i removed all plug wires one by one and couldn't isolate any particular cylinder...she stumbled equally with each one unplugged. i may try new wires anyway as the ones on are old. i did notice a ticking/clicking noise coming it seemed from the cylinder #6 end of the engine underneath the valve cover. could this indicate a valve problem? saw some exhaust come out from where the pcv valve inserts in the valve cover but not a lot. i think this is normal? i have also noticed she is running on the cold side...about 53 degrees C. usually she was between 60 and 70. i'll probably change the t stat, doubt if its related....so how would i check for valve problems?

 

[greno]

You check for valve problems with a compression test.
How long since you gave this engine a tune-up?
Plugs, points, condenser? Maybe wires.

 

[achris]

Running that long with one cylinder down could cause a range of problems. You will almost certainly have pulled water back into that cylinder through the exhaust valve. Running a compression and leakdown test will help identify any issues. Check the oil for signs of water ingress.

The other thing that will have happened is the spark for that cylinder will have gone somewhere, most likely caused some tracking inside the distributor cap. I would be replacing the cap and rotor straight off. That could lead to this rough running, and even the valve tick you have...

Chris.......

 

[greno]

Your temp was down because you're only firing 5 cylinders. And a little lifter tick in a 40 year old engine is common. I wouldn't worry about that unless is gets loud. If you spend long hours at idle or slow speed while fishing you may get some carbon buildup. Even more if the engine hasn't been tuned in a while. Give it a good tune-up. Take it out and run it above 3500 RPM for a while and then see how it sounds. If it still doesn't run better then do a compression test to check valves.

 

[KJM]

i checked the timing tonight and it was advanced to far which was odd as i had set it only about 3 weeks ago when i put on a new distributor cap, rotor and cleaned points and mechanical advance. could the weights under distributor plate be not retracting and causing the advance to stay too high from high rpms to idle? but the miss was still there even after i reset the timing. i have an extra distributer cap, i'll put that on tomorrow and try her again. hop.efully it's something that will work out of her with a good run.

 

[Scott06]

Yes advance weights could be sticking, check for free movement when you do the cap. I would also ohm out the plug wires or just replace, if one fell off you may have arced in the cap end, I've seen that damage the core and lead to high resistance.