I have a 2001 S40. The fuel injectors are new, the spark plugs are new, the ignition coils are new, and the idle air speed control valve is new. The engine will turn over just fine but will not fire. When you try to crank it up the exhaust smells heavily of gas. No idea whats wrong. Any help would be greatly appreciated!

 

Remove the upper timing belt cover and check if the timing belt is broken or loose. Also check for oil on the timing belt. It should be dry. If you have a compression tester do a compression check.

If the belt is good then remove the left most spark plug (when facing the engine). Place the plug in the spark plug boot and press the very bottom electrode against the metal top of the engine. You want to be holding the rubber part of the spark plug boot to avoid shock. Now have someone crank the engine while you look for a spark at the plug. It should be "electric blue", not yellow or white.

If the above checks out then check fuel pressure. You smell gas which suggest the fuel pump is good however that does not mean the pump is supplying proper pressure. For this you need a fuel pressure tester. Harbor Freight sells them for about $20. If your car finally started after a long cranking time then it's usually the fuel pressure regulator.

The only other thing left is air. Check your MAF to be sure it's hooked up and clean. Air filter is clean. All the normal stuff to make sure it's getting air.

Have you checked for trouble codes? Harbor Freight also sells cheap code readers. I'd get the CAN-BUS compliant one because you can also use it on later model cars.

Timing belt intact, tight, and dry: