Car is a 96 z28, recently had a code come up saying catalyst failure, we relpaced the cat and the code came back on so i'm thinking its the o2 sensor. The car has gradually gotten more and more hesitant while trying to start it, I think its a fuel problem. If you give it gas it will sometimes start up on the first try, especially if I have recently driven it. Should I start by replacing the fuel filter and then go from there?

 

If it takes a long time to start when its been sitting for a long time, but starts ok whith-in minutes of shutting it off the the check vavle in the fuel pump is bad. It has a valve in it that holds pressure in the fuel lines when the pump is off. If its bad and the engine is off for a long time the fuel in the lines leak back into the gas tank so when you go to start again you have to wait for fuel to go from the pump, to through the lines to the engine, to the FPR and build up enough pressure at the regulator to meet required pressure at the injectors again. the pump itself is probally putting out enough pressure but the check valve inside is not working anymore.

 

Attach a fuel pressure gauge to the Schrader fitting on the back of the fuel rail to determine if your check valve is working properly. Turn your ignition key to run (not start). Your fuel pump should prime for 2 seconds. Your fuel pressure should rise to approximately 35 psi and then only slightly drop when the pump shuts off. If the pressure drops quickly, then your check valve is dirty, you have a leaky fuel injector or your fuel pressure regulator is faulty.

 

Would those problems cause a loss of power?