Engine not running on all 8

[ironnut]

I've been playing around with this for a while now. '76 350ci HEI on top of distributer. It used to not start on all eight, then after it warmed up it would. Then I changed plugs and it started running good then i went for a drive and about 30 miles later it went back to running crappy. Since then I replaced wires, cap and rotor. Pulled all the new plugs and cleaned them, still doesn't run on all 8. One plug was oily compared to the rest, but i cleaned it. My only thought is that the plug is fouled and I need to replace it. Any suggestions as to what I havent thought of, maybe the one cylinder just has worn rings and is fouling out the plug. Thanks

 

[1985_K5_Silverado]

Have you hooked up a vacuum gauge or done a compression test?

 

[ironnut]

not yet, compression test was next, but even with low compression it shouldn't miss like it is. I replaced the two plugs that I thought were the problem but its the same thing.

 

[ironnut]

Just fired her up again and it seems to be runnin alright, gues replacing those plugs did help, I got a lot of oil on the one plug, the engines about due for a rebuild, after all it is 30 years old.

 

[diesel4me]

probably..

You might have a few valve stem seals missing or broken,letting oil drip past the stem and guides and fouling the plugs out eventually..replacing them isn't that hard,but it takes the better part of a day,and you need an air compressor, or nylon rope stuffed in the spark plug holes to hold the valves shut when you take the valve springs off...

Speaking of valve springs,you may have a weak or broken one..we had several motors we "woke up" at the junkyard after sitting for months,that had the same symptoms as yours does..they would start up and run on 6 or 7 cylinders for several minutes, until the valve that was sticking open would suddenly break free as the heads warmed up,and it would hit on all 8 cylinders again..you might have a sticky valve,a weak or broken valve spring,or a hydraulic lifter thats either collapsed sometimes(would tick loudly)or one that is pumped up too far(no noises,but holds the valve open slightly)...