Crank but fails to turn over?

Checked fuel pump. Buzzes primes etc. Have strong stream to rails. Replaced cam sensor, Crank sensor, ASD relay. Checked fuses all look good. Checked Grounds by left headlight by transmission. Couldn't see the one on passenger strut. All seem tight, although I don't know how many there are. Read there's 5 major ones and a slew of little ones. Have to Google diagram. Dash lights up everything. No check engine n because we took batter out to charge, we erased any codes before knowing what issue may be. Checked injectors, spark plugs, coil pack. All are fine. The only thing I didn't check was the starter motor. But it cranks so I don't know if it could crank and still be bad? Checking MAP sensor tomorrow. The throttle body is fine. We sprayed ether into to it, but it wouldn't start again. It acts like it wants to but just can't get over that hump. The engine seems very well taken care of so I'm not understanding underlying issues. Person, I bought it from said it was running perfectly then just died. Had it towed and mechanic didn't really want to be bothered after doing these same things and not finding the fault. Diagnostics on the engine are very good. I'm praying it's not ECU or PCM issue. Can you please tell me which way to go?