cylinder misfires

My 2001 Dodge Ram 1500 started running terrible all of a sudden. i figured it was in need of a tune-up, even though I did one about 20,000 miles prior. I was shown how to retrieve my engine codes. the first code that came up was P0303(misfire in cylinder 3). I took it to my local dealer, who said that cylinder 3 had only 5lbs compression. they said they wood have to tear the motor down to find the problem(much money). I was going to take it to another repair shop when it started running better than ever( no codes). I have never heard of a bad cylinder repairing itself. About 2 months later it started running bad again, except that now I have codes P0303 & P0306. To make a long story short, I have replaced the PCM, both oxygen sensors, map sensor, cam sensor, crank sensor, coil, cap, rotor, wires(twice). I have a new catalyic converter, but have not installed it yet. I have taken it to three repair shops, and all of them are befuddled. Please help!!!

I just got through two months of trying to figure misfires out. Turned out that what the mechanic called a "bad load of fuel" left three gallons of water in the fuel tank. If the misfire is fuel level related you may want to check for water.

Check the vacuum line to your map sensor. I had one that was
soft and spongy and caused me a lot of problems before I found
it. It's probably not your problem but it would be a cheap fix if
it was.

have them check for a vacuum leak...these vehicles leak underneath the plenum..

Same type of problem with #5 cyclinder. I thoguth that maybe it was because of platium plugs instead of standard plugs. Will heat get the water out, if it was a water / fuel problem? Mine is a 1999 with 60K on it. The missfires felt like a slam in the transmission. The trans shop said the code reader said number 5 misfire. Would fuel level always cause the same cyclinder to misfire?

I have a problem that started right after my wife filled up a few weeks ago. This is a 1992 B350 with the 360 FI engine.
When it warms up and you are traveling with very minimum acceleration it will "cough" just almost like a backfire through the carb. In fact that pretty much describes it. If you floor it the van takes off like a scared rabbit. I thought it would start failing when I took up a steep hill.....just goes great but if you are going 25mph and ever so slightly start to speed up it will do it's cough. I checked everything but the fuel filter because I have been told it is in the gas tank.
Would a clogged filter do this? I thought it might be water in the tank but I've added some additive that is suppose to clear that up and it still does it's cough. No engine codes. Doesn't do it all the time and at 70mph for two tank fulls it only did it trying to get up to 70 and then ran without a hickup until I had to stop again for more fuel.

Any ideas?

There are a number of "mechanical" things that could be the problem. Water in the tank is certainly one of them. If that's the case, drop the tank, and drain it.
However, there are a few other things that can cause these same simptoms. Bad spark plug, or a bad spark plug wire. Wrong heat range plugs, A clogged or nearly clogged filter, an intermitten transmission problem, bad coil, or coil wire.

I would start with the easy stuff first. Check for water in the gas, check your plug and coil wires, and gas filter. Any of these problems can be constant, or intermitten.

My old 76 B200 used to love to eat plug wires, and it was always the #6 plug wire for some reason. The problem was the skip only happened when the engine was under load, and i had already changed the gas filter. We then used the "In service Method". :screwy: I removed the engine cover, and had my brother-in-law remove and replace the plug wires one by one while I drove the van slowly up hill (keeping the engine under load). When he removed a good wire, the rpm of the engine would drop. When he removed the bad wire, there was no change in the engines rpm. That's how we knew we had the bad wire.
Yes, it's a crude, but very effective method. If you try this, DON'T DO IT ALONE! Have a friend pull the wires while you drive. You will need a plug wire removal tool so you don't get shocked or burned. Mechanics gloves aren't a bad idea either.