Misfiring

Hey everyone. So i have a 86 accord lxi hatch and its been giving me problems. Since I got it it was okay and when I drove it it was fine until it gets warmed up it starts losing all power past like 2k-3k rpm ill step on the gas and it wont go it sounds like its dying or going to cut off if i push on the gas. Its gotten worse now it has a heavy misfire and Im not sure what the problem is. I have replaced the injectors, spark plugs and spark plug wires, o2 sensor, and cleaned out the distrubutor cap and rotor. Only thing I havent changed is the whole distributor itself. I should also mention I took off the original exhaust off and hadnt replaced it yet and it was fine for a bit (it increased the rpm and response for sure)but im not sure if it can cause some weird idle issue if its off or not. My car used to run fine but when I start it up it sounds like a tractor now, its not knocking but its misfiring like crazy and I cant figure out why. Also I can hear a slight hissing in the engine bay like maybe there is a vacuum leak but im pretty sure I ran through all of the hoses and found no leaks or cuts of any kind. Has anyone experienced this before on thier accord? Thanks in advance.

Pull each spark plug and look at them it should tell you what cylinder is missing. If you can with the plug out you can do a compression test of the cylinder and see if the piston rings or the valves are shot. I would replaced the spark plugs new with plain NGK spark plugs properly gapped.

Also since you have changed some parts did changing the parts make the problem worse or better? Maybe spark plug wires crossed up, injectors not snapped in?

Took it to the mechanic and he took out the spark plug wire and found out cylinder two is misfiring. He said it could be a bent valve or it may be the piston or block thats messed up. Ill keep this updated every once in a while.