My 69 442 has a miss on the left side at idle, vacuum holds steady 20. I tried removing each plug wire but didn't notice any difference. Engine runs smooth and strong under load and WOT. All plugs are new and clean, wires are new. Compression reads 210-215 on each cylinder. What else can I check? Thanks

 

since you have gone this far have you checked cam... with valve cover off are any of rockers loose or have a push rod not touching when you turn crank manually or bump ignition to look for rocker not moving or restricted movement during all the timing cycle to see if anything indicating worn cam lobe or collapsed lifter, bent push rod, hole in rocker arm(factory) or bad roller(roller type)arm, worn timing chain or in some case a little of all... this would cause a miss and not effect static compression test on each cylinder... I know it usually affects an engines power a lot when you restrict one of the intakes on one of cylinders but the engine runs at just under 1000 rpm at idle and even something just starting to go in the heads breathing can begin to be audibly noticeable... but you are testing compression while engine is still right? As the engine moves through its firing order it may only have the miss on the one cylinder if head is having trouble breathing through one of its intake or exhaust valves... you did say it was on one side... try taking that sides' valve cover off first and check... then try other side if you don't see anything on the side you say you are hearing it... just a thought

 

What about your points, condenser, cap and rotor, when were they changed last. Dwell/timing checked also?

 

I'm kinda curious as to how you know it's on the left side. That information may help to narrow down the possible causes.

 

+1, since pulling individual plug wires didn't change anything.

- Eric

 

The exhaust on the left side has a steady "spit" for lack of a better word and the right side is steady. The distributor was replaced by a new HEI system a few months ago and ran smooth prior to this. The engine had complete head work done (new valves, guides, seats) a few thousand miles ago. Engine ran perfect on road trip and two days later when I started her back up this "spitting" started. Thanks for all suggestions.

 

Have you connected a vacuum gauge to check for evidence of valve leakage?

- Eric

 

Yes, first thing I checked, holds steady at 20

 

This'll be a tough one...

You're sure there's no tiny exhaust leak anywhere from the manifold / header to the tailpipe, right?

- Eric

 

Hmm steady spit on one side... at what interval?... many spits per second or second/s in between? just wondering... haven't "heard" it... spits out exhaust with no converter I have heard usually involved an exhaust leak past header or unburned gas from combustion or (shudder) antifreeze from head gasket failure or even oil spitting from blow by on a severely worn engine (scored cylinder on that one)... anyhow what is causing spit is what I am trying to get at... having recent work is suspicious... issues pop up a lot of time after the break in on builds... I have had problems after a fresh tune-up with a new distributor cap I bought that caused one cylinder to not fire all the time (though that made a stink out one side of unburned gas)... so just trying to get clues

 

The "spitting" is continuous like a bad plug wire or spark plug but there is no sign of a fouled plug. What gets me is that when I pulled each plug wire there was no difference in the exhaust. My first thought was a vacuum leak but that would affect both sides, wouldn't it? Checking exhaust connections next. Thanks again.