Misfire 1.6 engine

Started to misfire, changed plugs, cap and rotor and wires, still misfires, we then changed fuel filter and all the injectors and it still misfires. what do I do now???

What cylinder is mis firing? Do you have good spark coming out of the coil? should jump about a half inch of gap without a problem!

Number 4 is not firing. If I pull the plug wires one at a time while it is running they all cause the engine run so bad it almost stops, if I pull number 4 there is no change at all.

First we put a timing light on each plug wire, they are all getting fire.

Pulled all plugs, cylinder 1 and 2 got 90psi first burst and built up to 155 psi
number 3 initially got 90 and built up to 120
number 4 got 60 and built up to 120
went back and rechecked number 3 and now it read 60 and built up to 120

As engine was running we pulled the plug wires one at a time and it appears to be running on number 1 and 2 only

I unplugged the maf and then plugged it back in and the engine ran a little faster when unplugged and when back in it then slowed again to where it was

What is wrong

how many v belts do you have, if belt is slipping it will cause you to get a check engine light saying engine misfire.