Starting Issues

[MarkT302]

95% of the time, my engine fires right up, but maybe 3 times a week, the engine cranks, but doesn't quite turn over. When it cranks like that, it sometimes starts(barely) and is at 500rpms and then kicks up to normal idle speed. When it cranks and doesn't turn over at all, I just turn the key to "off" and then try to restart it and it fires up just fine. Any idea what is causing this? The battery is fairly new. It's a 4 month old Motorcraft battery. I don't think it's the starter, either. Alternator?

 

[J_C]

Is it cranking slow or is there any pattern like wet weather or cold?

If you have a bad alternator it may not charge the battery well or be leaky to the extent that the longer the vehicle sits, the further it drains the battery, BUT the alternator plays no direct role in getting the vehicle started, you could take it out and use a shorter belt and get it started still... not that you'd want to, just saying.

Regardless the battery doesn't seem to be a problem since it starts on the 2nd attempt, though if you have a multimeter you could still check the battery voltage.

I'm wondering if either your fuel pump, an electrical connection, or a relay is failing intermittently. Can you hear the fuel pump come on? It would be easier to hear if one person is under the vehicle near the tank and another turns the key, but not turned far enough to start, just to get the fuel pump energized.

Have you cleaned the IAC valve recently? I don't know if that would prevent it from starting but could change idle RPM.

 

[2000StreetRod]

weak fuel pump?

The fuel pump only runs for a few seconds when the ignition is switched on and then continuously when the starter is cranking. I suspect that you have a weak fuel pump that isn't producing normal pressure in a few seconds. You might try switching the ignition on, off and then on a couple times before cranking the starter. If that fixes the problem then you have a fuel pressure problem. Or you could just measure the fuel pressure. If its been more than 50K miles since the fuel filter has been replaced do that first. That will increase the life of your new pump when you install it.