Why does the engine turn over but won't start after ignition replaced ?

There could be several reasons why your 2002 Altima won't start even though the engine is turning over. Here are some common causes to consider:

1. Fuel system issues: If the fuel pump, fuel filter, or fuel injectors are not functioning properly, then the engine may not be getting enough fuel to start. You can check the fuel pressure and fuel pump relay to see if they are the issue.
2. Ignition system problems: If the spark plugs, ignition coil, or ignition module are not working correctly, then the engine may not be getting the spark it needs to start. You can check the spark plugs and ignition coil to see if they need to be replaced.
3. Battery issues: If the battery is dead or not providing enough power to start the engine, then the engine may not start. Check the battery voltage and connections to make sure they are in good condition.
4. Starter problems: If the starter motor is not working correctly, then the engine may not start. You can check the starter relay and wiring to see if they are the problem.
5. Mechanical issues: If there are any problems with the engine's timing, compression, or other mechanical issues, then the engine may not start. This would require a more in-depth diagnosis by a mechanic.

It's best to have a professional mechanic inspect your car to determine the root cause of the problem and make any necessary repairs.

I don't know if this is helpful but an engine needs three things to work. Air, fuel, spark.

Won't turn over? Do you mean the starter won't crank the engine over?

Or the engine cranks over and won't start, and you have tested for spark when cranking and have no spark? And then you have tested the coil and ignition module, and they tested out good? Am I on the right page here? If so, maybe the next thing to check would be the crank position sensor. The ecu (computer) signals the ignitor (ignition module) when to initiate spark after it digests the signals from the crank position sensor and the cam position sensor.

If it is a 3.8 engine change the crank sensor,they go bad on the 3.8 engines.

call your dealer

i know industry jargon can be confusing, but lets try this. if it turns over but won't start, it could be your ''ignition module'' that sits on top of the vave cover on the motor or it might be the fuel pump or filter. make sure when you crank the engine that the key is all the way turned or it may not always make a proper contact to activate the ignition module. iv'e seen this before & had to change the ignition switch & all worked ok after that. i would need to know engine lt size to give you more details on the matter. please get back to me.

If the engine won't fire up, but your starter turns over, you may want to check your timing unless you have a check engine light on. If the CEL light is on, have the codes scanned.

If the engine won't turn over with the starter or it clicks, have your battery tested at autozone or advanced auto parts. Replace the battery if it is bad. Else, have your starter tested.

If the engine still won't turn over and the battery and starter are tested fine, you may have a blown fuse, bad ignition switch, or a failed relay.

If the engine fires up but randomly dies and starts back up, you either have a failed sensor, failing fuel pump, clogged fuel filter, bad plugs or wires, or a failing ECU.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

This happened to to me with my ranger. I went and bought in ignition and a junk yard and no problems after that. That way your not out of a lot of money.

It could be that your fuel pump is not getting enough fuel to the engine to start it. Is your starter turning over or trying to start the engine.

You mean that the starter is turning (cranks) the engine but the engine won't start? Be sure it is getting fuel. Turn the key to the on position and you should hear the fuel pump in the fuel tank run for a few seconds. If so that is good. If the fuel is being delivered then possibly you have no spark which usually is the electronic ignition module. The only way to test it is to replace it. Your timing chain or belt could be broken or "jumped" as the third possibility. I am leaning toward ignition module being bad as they just die without warning and nothing can revive them.