Boxer won't start
 

My battery was failing on a 2003 Boxster base. Finally, I got the front hood open, replaced the battery, now the engine just turns over, but will not start. Car gas been sitting still for a good 4 months before replacing the battery this week. Any advise welcome. Yes it has high octane fuel in tank. Bob

Need to check for fuel and spark.....
Fuel pump relay good?
Crank position sensor (CPS) failed?

It turns over, it just won't fire.

What dghii said. You need to check for fuel and spark. You can find multiple posts to guide you in doing that on this forum.

Pull off the vacuum hose at the throttle body. Have an assistant crank the motor and at the same time spray wd40 into the hole in the throttle body. If the car sputters then you are not getting fuel. No sputter means no spark.

I am surprised no one has mentioned the crank position sensor. If it is bad you will get exactly these symptoms.

It was mentioned in first reply. To the OP, I know it may seem like you're not getting help, but you are. Our cars are like any other vehicle...no start is either caused by no fuel or no spark. The CPS is part of the "no spark" chain.

Not sure on the what the minimum voltage you should see while cranking but with my 84 Alfa, its possible to have a condition where battery is strong enough to turn starter but not strong enough to supply minimum voltage (~10.5Vdc) while cranking to enable the Bosch L-jet fuel injection. Result is cranking but no start.

If the tacho is rising while cranking, then the crank angle sensor is OK.