cranks but no start

How are you determining that the spark is weak? I would check the fuel system first. Check for a tripped inertia fuel cut off switch in the back. Then, check for solid and steady fuel pressure as normal. If this is all good, then you need to check spark. And before all of that, make sure the red anti-theft light proves out or stays solid when you put the key in. If it's flashing, you have an anti-theft issue...

check the vacume lines..if a certain vac line is broken then the engine cant start from improper air fuel mixture to maintain steady combustion in engine..