Car won't start )=
 

So I bought a 03 coupe for deals - it wasn't running . The previous owner said it was driving fine then just stopped working .

I put a new battery in it and sometimes it cranks - but it's a very slow & uneven cranking . And other times it just clicks . Sometimes I'll hear a weird camera shuttering noise coming from somewhere under the hood . So far I've changed the battery , the crank & cam shaft sensors , the throttle body , mass air flow sensor , spark plugs , starter (not in that order) .

There's also a date and markings that suggest a previous owner had gotten the timing done in 2021 from a shop .

I have no idea what is going on with this car . My next move was going to be replace the alternator & check for a bad ground .. other than that I don't know what else I could do .

​​​​​​Could it possibly be a bad ecu ?

​​​​​​Any suggestions would be great .

Check all of the relays and fuses in the circuit. Is the fuel pump priming and hitting proper pressure?

I'd focus on the starting circuit to find out why it won't consistently and STRONGLY crank the engine.

Put it on a charger to make sure it's not the battery, just because it's new doesn't mean it's charged and that "chattering" is common with a discharged battery.

Once you know the battery is fully charged, if it's still not strongly cranking clean BOTH ENDS of both battery cables with a wire brush, there's also a jumper from the passenger/right side of the timing chain cover that lands on the chassis directly below the coolant reservoir. Those cables all need to be very clean or you don't have a good electrical circuit for starting.

If it still cranks weakly then remove and bench test the starter, when they fail they can either stroke out dead or die a slow death and start cranking more and more sluggishly, it sounds similar to a discharged battery.

Once the car is cranking properly THEN move along to any other troubleshooting steps, I strongly recommend not just throwing a bunch of parts at the car (with the exception of spark plugs), especially things like cam/crank sensors (due to these engines only working with OEM Genuine Nissan or Hitachi brand ones) because it costs money and the old ones are likely still perfectly functional.

If one of them is bad the engine will almost always throw the check engine light, regardless you should OBD2 scan to see if there's any codes stored that aren't tripping the CEL light.