Cranking and not starting

Hello

the car is a 1997 Nissan maxima. 3.0L
when ignition is turned on there is cranking and will not start.
1-we checked for power and there is power. **Where did you check for power**
2- we checked fuel there is fuel.**Did you see it or smelling it**
3 we checked for sparks there is a weak spark occasionally.**What color is the spark**
4-checked crank sensor, its ok.** How did you check it**
5-sometimes while cranking gives a backfiring sound.
still looking for the problem please advise.**Try checking the timing belt-if it has a distributor remove the cap have someone crank it over-is the rotor turning?**

thanks

Answer the above before we continue.

Happy Easter

Rasmatazism