Alrighty so I am pretty sure I know the issue, but im pretty sure its not worth sinking money into at this point.
1993 F250, 351W, 186ish,000 miles (I dont know if its accurate). All cylinders are between 95 - 105 psi *low I know, air was just shooting out of the oil cap*. The 351 is due for a rebuild. But that requires time, parts, and money, which I am slowly trying to accrue all 3. However about 2 months ago she started to have a slight slip of a misfire at idle about every 10-15 seconds. I personally thought it was the valves being worn out judging by the cylinder pressure. However it has now started to do it very aggressively, probably about 5-7 times every 15 seconds now. And now I am losing about 1 liter of coolant every 2-3 weeks. However she only starts doing the misfire when its warm outside, if it cold in the morning she does not. However she will start misfiring once she is up to temperature regardless of outside temperature. Also the misfiring completely goes away whenever I accelrate or stay at speed. But as soon as it idles it comes back. I drive roughly 50 miles each day for work. And im really not wanting to replace the headgasket on an engine which is going to be replaced this year, I have thought about those headgasket sealant bottles however I would rather not clog my heater core. Any ideas/thoughts?

 

Where is the coolant going? Did the engine spring a leak? Pressure test the cooling system. Have you removed the spark plugs to see if they indicate coolant being burned?

 

What color smoke are you getting out of your exhaust when it acts up? If white, then yes, coolant is getting into the combustion chambers. Blue is oil, and black is fuel. If it is white, then I would agree with you that its possibly a head gasket. The bottle sealer stuff works ok-ish, if done right, but, obviously not a long term solution.
Also, when engine is cold, if its a coolant leak, it won't act up as thermostat is still closed til motor warms up, so no coolant flow to the motor, other than what is in the motor already. This is honestly just a guess though. With that low of compression you could have other issues as well. A fresh rebuild, when you can, will really make that motor hum. I did my 460 few years ago, and night and day difference over stock, and complete rebuild.

 

Did you try doing a "hot" compression test? Get the engine up to operating temperature, and then pull the plugs and test your compression.

 

Update: Well I believe I fixed the misfire, although I have no idea what I did. I will go through the order of it all.
#1 I pulled some plugs to see the condition, cylinder 3-4 have a slight bit of oil around the threads but nothing that will cause a misfire, #2 I pressure test 3/8 cylinders, they now average low 90s, #3 I pressure test the radiator while running, pressure never drops where I placed it at 15 psi. #4 I shut off the engine and then pulled a distributor cap and rotor arm and replaced them with new rotor arm and cap that I had laying around. No difference when vehicle ran. So I took off new rotor arm and cap, however this time I follow the firing order instead of just copying what the previous cap had on it (mainly because I lost track of how it was) 1-3-7-2-6-5-4-8. I also reset the battery by disconnecting it and touching negative and positive together for 20 seconds. #5 I started her up and she was no longer misfiring like crazy. I have no idea if me shuffling the spark plugs wires around caused a wire not to ground to the engine block, or if the firing order was incorrect, or if there was a code causing all of this. This didn't seem like a firing order misfire, it was to random. This puzzles me.

I appreciate all of you for your help and suggestions though!! Thank you guys sincerely!!

 

I am just curious, how much oil does your engine use and how is its power?

I wouldn't worry about the coolant loss if it doesn't look like it is getting into your oil.

 

Well she only recently started to use oil in the past 2000 miles surprisingly. So as of now I am just going to say 1qt per 1000 miles. As for power she is definitely behind any modern truck on the road in terms of acceleration, but I cant compare her to any rebuilt 351W because I have never been in F250 with a good condition 351W. To be honest I have only ever driven 1 obs, and that is mine. But let me tell you that power doesn't matter when you hear the roar of her exhaust going through a 4 inch exhaust pipe and resonator more than makes up for it. Her hum while chugging along makes me keep putting money into her, I never want to get rid of her.

 

That engine may run a long long time without a rebuild if you want it to. If it gets to using too much oil for you liking, try adding a quart of Lucas oil stabilizer. Good luck with it.

 

There was a service bulletin about ignition wire crossfire but whatever way you have them now is fine since you said it is no longer misfiring




You could be losing some low end performance because 4” exhaust is is way too big for a stock engine. I am currently replacing the 302 in the pickup mostly because it used a quart every 600-700 miles. I drove it for several years that way.

 

Update: It came back, I am genuinely perplexed at it. When I start her in the morning (8 AM) it doesnt misfire, however when I drive her to work and park her it will. Which made me believe it had to do when it was at operating temp. However after I get off of work at 6 she starts doing it immediately at start up and when I shut it off (idling before shut off). If it was completely random I would think it would be burnt valves (which to be honest with a truck at the age of mine is to be expected), however it always happens in this order. I dont know what it could be.

(edit)
This is my semi theory. When the truck starts in the morning the oil is thick enough from the cold that it can not enter through the piston rings. And I dont let her idle long enough to warm up and feel her misfiring. But when I get to work she is warmed up and the oil is thin enough slip through the piston rings causing random periodic misfires. And when I start her up after work, the temperature of the engine oil has gone up by at least 10 ish degrees from atmospheric temperature. Making her just viscous enough to slip through the piston rings causing random periodic misfires (although not as bad as when she is completely warmed up). This is all that I can come up with....
Any thoughts?

 

If youre sure its not ignition based mis-fire, then how about a sticking valve. When valves stick, the valve is held open for 1 or more combustion cycles and it causes a very noticeable miss which is usually related to heat. Sometimes, a quick jab on the throttle will unstick the valve if its stuck for more than 1 combustion cycle. You can try throwing your favorite "mechanic in a can" in the oil and see if it frees up the valve.