I have just recently started working on my s40 again. I put it on a code reader and it ended up having faulty 02 sensors, I replaced those and it is no longer putting out any fault codes. However the engine just refuses to fire. Have no idea what it could be. Any help is greatly appreciated. Thanks.

 

 

The video above is a good step by step process for anyone. Fuel, air, spark, and timing. Test, test, test

Have you removed the timing belt cover to see if the belt is intact and tight while cranking? A broken or jumped timing belt will definitely cause a no-start.