Longishtime reader, first time poster! cylinder one is dead. Truck sat for 3 years because it needed a head gasket. Replaced head gasket, relapped valves, emissions delete, new distributor, fuel pump, cleaned fuel tank, new 1bbl carb (china), plugs, wires, cap, rotor, coil, spark computer (sorry, I'm still new here), vacuum hoses...everything. no heat riser, stock intake/exhaust (no cat). After replacing the head gasket compression was 75, 100, 110, 110, 100, 110. Wet test brought cylinder 1 up to the rest. Marvel mystery soak for only 30 minutes or so became 90, 105, 110, 110, 110, 110.

Timing is good, vacuum gauge flutters between 10-15 at idle, leakdown test says cyl 1 is tight but if i pull the plug wire with it running, there is no change. Verified plug is firing. The part that is making me crazy is on cold start the engine sounds perfect for 1-2 seconds, then immediately goes back into the misfire. Is it still the rings in cylinder 1? Maybe they're tight when the engine is cold?

 

Rings are loose when cold and tighter when warm.

Swap the plug between cylinder 1 and 2 and swap the wire with 1 and 3. See if the misfire follows the component onto another cylinder. If that doesn't yield results do a leakdown test.

 

I do like the plug & wire swap for seeing it is it one of them, New dose not mean good.

My 81 had a vary bad bucking issue under a load, really showed up pulling a trailer, but idled just fine.
I did pull the vacuum to the dist. to see if that was moving the plate moving the wires that might be broken but no change.
I did not think I had that many miles on the full tune up but after thinking about it I had 10K to 15K

Cap & rotor checked good, I had a spare (used) ICM no change.
Swapped carb as I had it and the one on was not 100% good, no change.
Well when I changed the plugs I found #4 was really bad and dont know how it was firing at idle?

My bucking stopped but now have a little miss I can feel all the time under even a light load, idle is fine.
I went to swap plug wires to see if the bad plug followed the wire but I pulled the end off the good wire so I replace them all, still no change.
I even changed the coil with no change.

I picked up a new cap & rotor as they were not changed just checked then got Covid and still knocked out today.
If I find the cap / rotor dose not fix it I have a new pickup coil for inside the dist. I will replace.

I should also point out the truck had a miss when I bought it, compression was good and a tune up fixed the miss so I never looked farther why.
I will be keeping an eye on that #4 hole to see if that plug dose the same thing or not.

Keep us posted what you find
Dave ----

 

I'll give it a shot tonight if I can get this baby in bed on time!

 

Swapped plugs and wires. Still missing. Pulled #1 wire and no change. Doing another MMO soak right now.

 

81 should be easy to pull the valve cover.
Get the motor up to temp and pull the cover with it off start the motor and watch the rockers for the hole that is miss firing.
My guess 1 may not be moving as it should like not opening all the way.

Now it could be a bent push rod, bad lifter or a bad cam and more digging is needed to find why.
My thinking the intake valve is not opening all the way.
If it was exh valve then you could be getting a back fire up the carb more so under load.
Dave ----

 

Fired it up without the valve cover on. Took a video so I could watch it in slo-mo. 1 seems to be moving as the rest.

I did notice some pitting on the cylinder wall yesterday when I was doing the MMO soak but it was about halfway down the cylinder wall which would make sense for the leakdown passing and the 15psi lost, but the fact that it runs perfect for 1-2 seconds on cold startup and that the cylinder is offering nothing after that is driving me bonkers. Could it be a lifter thing? Maybe getting a little stuck after they start moving? Video below.

 

 

Man that sure looks dry. Is there any oil getting up there? or is it there and just can't see in the video>
What inis your OP.

 

I was looking at the vacuum gauge fluttering between 10-15 at idle and Google came up with this below.

https://www.google.com/search?q=vacu...hrome&ie=UTF-8

It points to a valves sticking and why I said what I did about the valves opening.
Low compressing also why I said check valves. Intake not opening to let fuel in cant fire it or build compression.

Link also said a miss fire and you say that is what started this thread.
So it runs on all 6 when first started then misses.
Have you checked for a vacuum leak at the head?
Use carb clean with a straw so you can pin point the spray at the head / manifold at #1 port.
See if that dose anything. My thinking is when first started the air / fuel mix is rich and why if fires but once it runs the mix leans out and you have a miss.
At this time it is the only thing I can think of to follow up on.

BTW I am fighting a miss under load, now a light load. Before a complete tune up it was bucking under load.
The only thing I have not done is a compression test since I got the truck, it was good then, or swap out the pick up coil in the dist.
Just a though for me, check for vacuum leaks at the head & manifolds.
Dave ----

 

I think you're right. I just fired it up and raised the RPM and I can hear some clacking in the top end around cyl 1. Sounds like a valve slapping. When we had the head off we relapped the valves and put new guides. Everything looked OK. Would lifters be a thing?

 

JMO but you have an issue with oil not getting to the top first off. Think I would focus on that first and then address the problem with #1.

 

Should it be chucking oil all over the place? Oil pressure gauge says it's good but...

Is there a diagram on oil flow somewhere? I couldn't find it googling. I'm happy to go looking for a problem! I spent 4 years finding this truck, I'm all in!

 

New parts aren't always that great, and the 'after' problem might just be another, unrelated layer in the onion. A surprisingly useful test to do here would be to go out at night, with the engine idling in the darkest conditions you can make, and carefully look over every ignition component to see if there's any electric-blue light being emitted - there should be none at all, anywhere. I had a 1996 5.0l start to stumble under load a few weeks back and was expecting that troubleshooting it was going to be very painful, expensive, and time consuming. It had gotten new plugs, wires, rotor, cap, pickup (which had gone bad after being replaced only 100 miles earlier; a Motorcraft DU-50), and all new silicon vacuum lines back in the summer. After watching the Uncle Tony's Garage YouTube episode on engine stumbling, I went out and looked it over that night. After my eyes adjusted, a faint but unmistakable electric-blue glow was barely visible down in the #1 spark plug well. Swapping out the wire didn't fix the stumble, so I put in a new plug; that fixed it.

 

I will certainly give it a shot! New development. Figured I'd replace the lifters cuz got only knows when they were done last. I was in a hurry to get out of there so I could pick up my 3-year-old. Soooo instead of adjusting the valves in the firing order, I went one two three, four five six it ran well enough for me to run it long enough to figure out what was wrong. We adjusted the valves in order and now it won't idle and still runs pretty rough. I haven't had a chance to get back into it. Hopefully Sunday.