I was driving my tib and everything was just fine. Later that day I went to start it up, and it just sits and cranks but never fires. How do I go about diagnosing this?

Thanks!

 

Well, it's probably either fuel or spark and there are many reasons why you wouldn't have either.

Check the ECU fuse under the hood.
If you have a code reader that shows realtime data crank the engine and see if you get a RPM signal. If not, could be the cam position sensor or crank position sensor.
Turn the key to the "on" position and listen for the fuel pump to prime after the car has sat for a while. If it primes then it's not the issue. If you can't hear it that doesn't necessarily mean it's bad though.
Use an inline spark checker to see if you have spark.

 

Already checked the ECU fuse. Don't have a code reader. I tried listening for the fuel pump, but I'm not sure exactly what I'm listening for? Where is the fuel pump located, by the gas tank?

 

The fuel pump is in the fuel tank.

Make sure the fan is turned to zero, turn the key to on but don't turn it far enough to turn the starter. It'll make a whirring noise for a couple of seconds and go quiet.

It'll only do it when priming the fuel pressure so it has to sit for a while first so the pressure will bleed off or the pump might not run at all.

 

^ x2 -- listen for a small whining noise coming from under the rear seats. It might only do it for a few seconds each time you turn the key before it stops.

Have you tried jump starting it? I doubt it'd work, but just one more thing to mark off the list.

 

CKP would be my guess, mines acted up on me twice. Does exactly as you are describing, just cranks and cranks. The ignition coils and fuel injectors power up after it senses crank rotation

Pop it out and clean it and put it back in, make sure the connection at the harness is tight and making good contact too.

 

The only time I ever got "cranks and cranks never starts" was when I had water in my gas tank. A cup of isopropyl alcohol and a bunch more cranking later, and it was good to go.

 

Have you tried giving it gas? If yes, then it should smell like fuel. If you haven't tried then try it. If it doesnt smell like fuel then its the pump/relay.

 

I think a loose CKP will also prevent fuel pump from functioning, so lack of fuel might not be a fuel pump problem.

 

<div class='quotetop'>QUOTE (majik @ Jul 26 2010, 10:37 PM) <{POST_SNAPBACK}></div><div class='quotemain'>I think a loose CKP will also prevent fuel pump from functioning, so lack of fuel might not be a fuel pump problem.</div>
It will. I spent the night in a scary parking lot and replaced the fuel pump the next day only to find that it still wouldn't run the pump or fire. It was the CKP.