fuel pump

[Dhunter839]

Pretty sure my fuel pump has went out on my truck, but I want a opinion before I replace it. I started my truck and it idled below 500 rpm for about 15 seconds, then shut offit only starts if I pump the gas, but then it runs like it needs new plugs, I have to pump the gas then the highest it will rev is to 4000 rpm. When I turn the key over I hear ot kick on, but I don't know of its pumping,

 

[RonD]

If you hear the pump for 2 seconds when key is turned on then pump is probably OK.
And if engine starts at all, even poorly, then pump is working

Could be fuel filter is clogged, it is in the frame rail under drivers seat, $10-$15.

In Park/Neutral engine should not rev past 3,500rpms, that is called the REV Limiter and is normal.

"Pumping the gas pedal" on a fuel injected engine lets more air in NOT more fuel, it is not the same as a carb engine with an accelerator pump.
So if "pumping" works then engine is more likely getting too much gas, not to little.

Couple of things to try:
Turn key on, count to 3, turn key off, repeat 3 times.
This will turn on the fuel pump 3 times to build up pressure.
Do not touch the gas pedal!
Now crank engine and see if it fires up.
If it starts better but slowly dies(again DO NOT touch the gas pedal), then change fuel filter and see how it does after that.

If it doesn't start or starts poorly then try this:
Turn key on
Push gas pedal to the floor and hold it there, NO pumping
Crank engine
Holding the gas pedal to the floor before cranking shuts OFF the fuel injectors so no gas should be going to the engine while cranking.
If engine fires up then gas is getting into engine so you may have a leaking injector.
Need to test fuel pressure to see if that is happening.

IAC valve(idle air control) is on the upper intake, next to the throttle, the computer opens this valve all the way on startup to allow more air into the engine, this valve can get dirty and stick closed so very hard startup, it can be removed and cleaned.

In the last few weeks has engine started normally?
Normal start(again not touching the gas pedal):
Crank engine
Engine fires and RPMs go up to 1,500(approx.)
After a few seconds engine RPMs drop to 1,000(cold engine) or 750(warm engine)

The high RPM at startup is the computer opening the IAC valve all the way, then the computer closes IAC valve a bit to set cold or warm idle RPMs.

If your startup has not been like this then a stuck or broken IAC valve could be the cause of your symptoms.

Pull off the Power brake hose from the intake manifold or the PCV Valve hose, this will let in more air for startup, see if engine starts better, if so pull the IAC valve and clean it.

 

[Dhunter839]

Its started fine these past few days, only time I have trouble starting it is after o fill it up, it normally starts as soon as i turn the key, but after fill up it cranks and cranks then starts, will try later and see what happens

 

[RonD]

I assume the CEL(check engine light) works(comes on with key on then goes off) and it is not on when engine is running.

If it was a hard start with gas tank low I would think fuel pump, but with gas tank full......??

EVAP system is the only thing that comes to mind but it always turns on the CEL even if it's just a loose gas cap.

The EVAP system pulls air out of the gas tank to prevent gas fumes from polluting the environment.
It uses the engine vacuum to do this.
If the EVAP system valve was stuck open then when you were filling up the gas fumes could be forced into the EVAP system and then sucked into the intake manifold causing a fuel/air imbalance at startup.

 

[Runnin'OnEmpty]

Also try depressing the red button on the fuel pump
inertia switch (located above passenger footwell).

I've been having trouble with mine. I suspect some of
these switches are too sensitive from the factory, and
even slamming the door will partially trip them. Some
have caused the plugs to melt from the high resistance.

 

[SenorNoob]

With that new a model there should be some kind of code if it even hiccups.