Oldcarmark, I think you're quite right. I am going to try to locate a shop that has a scope (and maybe a tailpipe sniffer) with hopes they will reveal the key here. I have been avoiding shops because they are almost certain to redo everything I have done and charge me for it, IF they are even knowledgeable enough about the old stuff to get that far. EVERY interaction I've had with shops as a customer has been disappointing and frustrating.

Pete, I have been as specific as possible short of posting video as to the behavior of the gauges and engine. If I have been vague it is because the answer is vague. For example, the vacuum gauge needle at the point of stalling might go from about 3 seconds of perfect steady 21" to 0 in a matter of about a second. I cannot carefully describe what it does in that second, so I say it "drops off". There is no steady decline, no reliable, consistent behavior except that it will reliably stop running when I put it in gear or turn the lights on once it's hot. There is an intermittent, and I mean random, inconsistent, miss that will occur in the hot idling engine at about 700 rpm. If I back the idle speed screw off to decrease the idle further, the engine will slow to a stop much the same way it would if I had turned the idle speed below 450 rpm when the engine is still cold. I can tell that this problem is trying your patience much as it is mine, so please let me thank you again for trying to work through it with me. Please know also that I am posting in part as a sort of journal/means of thinking "aloud" as I try to work through this. The odds of a weird problem like this being solved without hands-on tinkering and observation are such that I can hardly expect a solution out of you guys, but it sure is helpful bouncing ideas around.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Sounds like a valve problem to me. You mention when it starts to miss the vacuum gauge drops a couple points with each misfire. When it starts missing if you can pull plug wires one at a time while watching the vacuum gauge the cylinder that is missing wont change vacuum reading.

Dan      Kingman Az.      86409

If you can find a shop with a good scope and someone who knows how to read the results there is no reason for them to want to redo anything.All you are looking for is a diagnosis using the scope.I would hope that with the advanced equipment they have today it shouldn't take long to see the problem.They use these on todays "computers on wheels".The ignition system on cars 50+ years ago are simple compared to what they have now.

  

lowrider, I am going to try that at the next available opportunity. If a valve or lifter is sticking, it must be doing it only partially and intermittently. It IS an item that could change with temperature and account for the behavior though, and I haven't tested for it specifically so I'll definitely have a go at it.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Cautiously good news!

I began to do as Lowrider suggested and immediately noticed what I believe to be critical information. I started the engine with the vacuum gauge attached and looked at the perfectly steady 21" reading. Then, I pulled a spark plug wire and what I saw was a small drop in vacuum, maybe about 1", paired with a slight pulsing fluctuation in the needle. This is not at all what the needle looks like when I'm getting my hot engine miss. That miss is a much larger, hard drop of 3-4" which immediately springs back up. If I were dealing with a spark or mixture-related miss, it should look like it did when I pulled the plug wire. So obviously I have misinterpreted what the vacuum gauge was telling me.

Since my pushrods are not bent and compression is good, I believe what is happening is one or more of the lifters is binding up on its way DOWN from the open valve position, when the valve spring is pushing the rocker, pushrod, and lifter back against the cam lobe. I think it is only a partial bind, resulting in slow valve closing intermittently. I know that there was an issue with the exhaust valve rocker on cyl #1 delivering oil to the top of the pushrod. Perhaps that lifter has not been adequately oiled.

Any suggestions for how I could conclusively test this theory, or fix it? I am thinking warm the engine up, change the oil, add a quart of MMO, and run the hot engine with the MMO for a time and see if the miss goes away. I am also thinking I'll pull the valve covers and visually inspect the lifters for oil coverage or anything else that might be weird.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

With your latest observation being 3-4 point drop on vac guage generally indicating sticking valve when engine warms up, i would have a look at engine running without valve covers on, usually theres not that much oil idling, place a few rags on inlet side and other places, watch for rocker arm wobble or p/rod runout, also try rotating p/rods to see if free. you could also shine timing light on these one at a time to get clear look at them. I realise will be harder when gets hotter but miss may develop then and you may be able to pinpoint any differences? Could you have a worn rocker /shaft and binding r/arm, perhaps later when cool, remove assy and check shaft for wear, then see if you can wobble any valves. Again, this is only my view re the sympton you describe and thats what i would do to try and eliminate things before proceding further, Good luck !

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

I recently had sort of a similar problem on a guys engine and it turned out the distributor vacuum was leaking very slightly so the timing would creep retarded until a small pop was heard, it was hard to tell the distributor was leaking. Also a defective condenser can cause a similar problem sometimes. A different distributor with petronics fixed the problem.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Billy, i agree with that, have thought that would certainly be worth the effort, and you just cant beat Pertronix reliability. Sure is interesting post.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

peeeot, also have you measured the voltage on the points side of the coil, I had a miss from mid range to top end once that I couldn't find, a low voltage on the points side will allow not enough charge in the condenser.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

Moz, the negative side of the coil shows 6.2V when the positive side shows 10V.

Billy, the vacuum advance is new and additionally I have been doing much of my testing with it disconnected.

I have made sure that I am not losing any timing when the car goes into idle or into gear. I have also done my best to determine exactly where on the crank damper TDC occurs, and as best I can tell, the damper markings are accurate within 2-4 degrees. I mention this because as I am working with the car right now it runs noticeably better at low speeds if I advance the timing to about 20 degrees initial. That makes no sense to me. It will quit right away if I retard the timing below 10 degrees.

I removed the driver side valve cover to look at the lifters and pushrods. They are definitely all oiling and spinning and not bent, with the exception of #1 exhaust, which is not oiling on the pushrod as mentioned. I moved the overflow outlet over so that the discharge of overflow oil falls directly onto the dry pushrod, but it didn't change anything about how the car ran. I did not remove the passenger side to look at it because I have looked at it before, not long ago at all, and it looked the same: rotating pushrods, plenty of oil everywhere, none bent. I am certain that has not changed.

Unfortunately I think I exaggerated the amount of a dip I was seeing in the vacuum reading. Certainly, it is larger and more pronounced than what occurred when I pulled a spark plug wire off, but I was really watching it today and the largest drop I ever saw was nearly 2", not 3-4. Most of the time when it would miss it would drop exactly 1". I pulled a wire again and the drop there with each miss was very small, maybe .25" of vacuum.

I took two videos of the vacuum gauge with the hot engine running. The first I took with the mixture screws out 1 turn. The second I took with the mixture screws out 0.5 turns. I would love for interested parties to take a look at these videos, as they show exactly what is happening, and how weird it is. I would be happy to email the videos; they are each under 800KB.

I was very hopeful that this was a valvetrain problem but it really doesn't look like it now that I'm testing for that.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive