i have an 2005 taurus i had the starter and fuel filter done about a year ago and the fuel pump done recently. my car is having problems starting , there is definitely power it was just turn over and wont catch. sometimes it will start right up but if i shut it off it wont work 1 minute later. could it be the crank sensor? im just having problems diagnosing the problem.
Does the CEL come on with key in RUN? If so, does the CEL go off when cranking? It it goes off, the crank sensor (CKP) is not the problem.
Have the battery load tested. 04+ are especially sensitive to low crank voltage.
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I thought I replied to this when you posted it. If you have a scan tool that can check the fuel pressure, check it. It's possible you have a bad pump again. It does happen. Do the test that Jeff says though to see if its the CPK.
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A bad O2 sensor will not prevent the car from starting since they aren't used until the engine has warmed up. A bad catalytic convertor is a possibility only if it's blocking the exhaust. Does the car have normal amount of power when the engine is warmed up?
Like others have said, start by making sure the battery is good (load test the battery or try jumpstarting it). Otherwise the next thing I would check is the fuel pressure. Your fuel pump might not be working every time (they tend to cause intermittent no-start issues).