I am running a Chevy 250. Recently replaced plugs, wires, points etc. during a tune up. Something i noticed in the process is that all six cylinders are firing good, and have good compression. however with the engine running i can take the plug wire off of plug 1 or 6 and the engine continues to run smoothly. If i take any of the others off there is a noticable drop. Is this normal for some reason?
I know i had posted this sometime back but just wanted to check and see if anyone had any updated thoughts on the situation.
BET THOSE CYLINDERS HAVE LOW COMPRESSION COMPARED TO THE REST. DO A COMP. CHECK.
check valve lift. A cam lobe may have worn out, happened to mine with similar symptoms. Also had worn valve guides and exh valves leaking on the weak cylinders, and very weak spring pressures. It would seal when turned by hand for measuring leakdown, and it would seal enough for a compression test to look good, but at idle it had trouble seating. my exhaust sounded like put-put-put-put-put-PHUTT
It looks as if you did not replace your distributor cap. Look inside the cap for evidence of carbon tracking. I doubt if this is the problem because you said it runs smooth, and I assume you can see spark when you pulled the plug wires. It's just one more thing to check.
Cross your fingers and hope it's a bad cap. That a lot easier than fixing low compression.
i did replace distributor cap, sorry forgot to mention that. Also this is a new engine "short block" valve train was completely redone new valves, springs etc. Everything on and in this engine has less than 20,000 miles on it. In running a compression test i am getting around 115 psi each cylinder. Could it possibly be in the ignition timing, (points setting etc.)
Have you checked for vacuum leaks? How about cylinder leak-down test?
Just curious-is this happening at an idle? If so, run it up to 2k rpm or so and try it. You may not be getting fuel to the end cylinders. They always run lean, anyway, and at idle they may not be getting enough fuel to fire.
you know Pritch i never thought of that, makes perfect sense though. I have been checking this at idle right around 600 rpm. Thanks for the tip i'll check it at higher rpm. Thanks