Problem starting F150...what gives?

have a 94 f150 5.0 dual tank pickup. truck won't start. I am getting spark and I checked the schrader valve at the injectors and gas is present....the battery works and yet all it does is crank, not turn over. what would cause this???? the only thing I could come up with was that perhaps the TFI was bad but I didn't have a chance to test it. any thoughts?