1999 Ford Windstar won't stay on

[Dipn2it44]

My van starts sometimes and runs fine but sometimes it won't start. Acts like not getting fuel. Once it does start it runs fine. Doesn't do it all the time but happening more frequently. The van will turn over but as soon as I let go of the gas pedal it just turns off. Any suggestions. I have put a new battery and changed the fuel filter. I don't think it's the fuel pump cuz it runs good once it starts?

[scubacat]

Test fuel pressure. Also check idle air control valve. Is check engine light on? Scan and post the codes here.

[12Ounce]

Relays ... they get pitted and burned, and unless you have super high voltage sometimes they are not lifted "hard" enough to get good continuity. It can take a bit of effort to find the exact offender(s) ... a voltmeter, a wiring diagram, and lots of patience ....are recommended.

[tomj76]

The fuel pressure is determined by just a few things, fuel pump output, restrictions in the fuel line, and fuel pressure regulator.

A bad fuel pump will never put out sufficient pressure, but a marginal pump or a restricted fuel line (i.e. clogged fuel filter) will put out higher pressure when there is little demand for fuel than when there is much demand. The new fuel filter at least takes that part out of the equation.

The fuel pressure regulator adjusts the pressure at the rail so that injectors always see the same pressure drop, so when there engine is at idle, the throttle is closed, and the manifold pressure drops (vacuum increases), so the absolute fuel pressure is reduced to keep the difference constant. Opening the throttle increases the fuel pressure since the manifold pressure increases (vacuum is reduced).

The idle air control is a digital step motor that adjusts an air valve to let a small amount of air into the manifold when the throttle valve is completely closed. If the IAC is damaged, it could pinch off the idle air completely. No air will keep the engine from running. I'm not sure of what test you should do to check this.

If you have a fuel pressure gauge, I'd test the pressure. If you don't have one, they are not very expensive, so I'd seriously consider getting one. I've used mine many times over to avoid replacing good parts of my engine.

FYI, I have a GM car that behaved like the fuel line was clogged (stumbled under throttle), the pressure tested OK, but I couldn't find the problem and replaced the fuel filter just in case. It a multi-port fuel injection engine. The problem turned out to be caused by a bad fuel injector that was very low resistance. Since all the injectors are wired in parallel, it was draining all the current from the PCM computer, and keeping ANY of the injectors from firing. It would work at idle because the injector pulse was short, but at acceleration the extra fuel taxed the electronics too much. Sooo, as you can see from this example, your problem could be something a little on the weird side.