I have a 91 ford explorer 4.0 that for some reason is getting spark to the 3 plugs and cylenders on the drivres side, yet on the passenger side it has compression and spark but when the plugs are pulled, the engine stays the same. It is running on 3 cylenders and I can't figure out why. Can you help me?

If you have spark are you getting fuel? Iam guessing the vehicle is fuel injected if so what type.( i.e.. Multi port, single port,etc.)