Ford auto mechanic?

[sanddrag]

That engine is Coil-on-plug and aluminum heads right? I'd check to make sure none of the coils have burned up and also that you haven't blown a spark plug out of the head. I've seen both happen on a 2002 F-150 with the 4.6.

How many miles on it?

Crankshaft or camshaft position sensor could be a possibility as well. Do you get a check engine light while cranking?

I'd check/clean the Idle Air Control as well.

[Ether]

128000 miles. It's still a pup. Last year it ran like a champ. Then sat unused over the winter (but I put StaBil in the tank, and started and ran it for half an hour every week, and charged the battery once a month).

The engine starts every time, and idles smoothly, quietly, and at the correct speed every time. So I'm pretty sure it's not an ignition problem. And for sure no plugs blown out.

My working hypothesis is that the fuel pump runs only during the brief period for a couple of seconds after the key is turned from OFF to ON. Just enough to pressurize the system so the engine starts and idles for a couple of seconds. Then the pump doesn't run any more, and that's why it starts misfiring and stalls out.

Anybody have any insight into questions 1 2 3 ?

[Mike dennis]

Once it starts idling have you tried maintaining a higher engine speed to see if it still dies? If that suddenly makes it maintain speed then you might just have a massive air intake leak.

Edit: I looked around a little and it appears that this is a fairly common issue on this car, they recommend checking the idle air control valve. then the fuel pump.

[Ether]

Hi Mike,

Cannot achieve/maintain higher speed with a higher throttle setting.

If it had a massive air intake leak, would it idle smoothly, quietly, and at the correct speed (as it does) ?

The idle air control valve controls the engine idle speed.

The engine idles smoothly, quietly, and at the correct speed. Symptoms do not appear consistent with a faulty idle air control valve.

[Mike dennis]

if it is only idling smoothly for a second or two then yes it can still do that, but if you get more than four or five seconds before it starts dropping then it probably won't be the issue.