Hard starting Each time i buy fuel i experience hard starting, i would have to pump the accelerator for some times before it starts. it happens only when i buy fuel. what could be the cause?

Damaged/clogged evap canister. You probably overfilled fuel tank one too many times and caused damage. Evap canister is kind of charcoal filled canister located on your fuel system vent. When tank is overfilled gasoline reaches evap canister and and makes charcoal to became hard like clay. Once that happens fuel tank looses its vent and fuel pump cannot pull fuel because vaccum created inside fuel tank.

hi Jaycee.
read up at this link.
5 Signs Your Car or Truck Has Dirty Fuel Filter DoItYourself com

What are some signs of a bad fuel filter? Symptoms of a bad fuel filter. One typical example of a restricted fuel filter is a vehicle that cuts out or loses power driving up an incline, such as a bridge. Under load,fuel demand increases and a clogged fuel filter reduces the needed flow. As the fuel filter gets dirty, the fuel pump works much harder.
Can a bad fuel filter cause your car not to start?1. Car is hard to start. One of the first symptoms of a problem with the auxiliary fuel filter is hard starting. If the filter becomes excessively dirty or clogged it may restrictfuel pressure or flow, which may cause the vehicle to experience difficultystarting.
Can a clogged fuel filter cause a car to stall?2. Engine misfires or decrease in power and acceleration. ... Sometimes the fuel filter can become clogged to the point where it negatively affects engine performance. A severely dirty or clogged fuel filter can cause the vehicle to experience misfires, a decrease in power and acceleration, and even stalling.

You sure filter is facing flow correctly?:I'd check that first,some cars/trucks have in-line filters.

All the above problems were happening to my truck, and the engine light never did come on. Finally changed the O2 sensor, and it runs like new again.

You don't say what the year make and model is.
I am going to assume it is fuel injected, so the problem could be a faulty fuel pump or check valve in the pump.
The fuel line should have some pressure before you crank the engine. If the line has low or zero pressure, it takes a long time to pump it back up enough to start the engine.

most time there will be signs of pump going bad. like loud whinning noises or hard start like having to spinn engine over for long time before actually starting did u experience any problems like that which made you pay for fuel pump

Hello
In my 25 years of experience I've really only seen few things that cause this, one is that the built in pressure check valve in the outlet of the in tank electric fuel pump leaks, this causes the fuel in the line and filter to flow back into the tank, this creates a void in the fuel line, the pump must fill the line and filter back up before pressure builds and the engine starts and runs smoothly, based on your description of when this happens I would say that is the problem with your truck. The fuel pump is located in the fuel tank, you must remove the tank from the truck or pull the truck bed off to replace the fuel pump. If you replace the pump make sure you also replace the fuel filter or the new pumps warranty will be void. I have a parts site that i order from on line, they are MUCH cheaper than local sources and only sell high quality aftermarket replacement parts as well as ACDelco and other OEM parts. Click here to access this parts site

its possible it could be the fuel pump have the pressure and the fuel volume checked with a gage and see how much the pump can pump gas in about 15-20 seconds,and compare to specs.

When going up hills is the engine bucking and missing? Also for the hard start warm problem, check the fuel pressure regulator for leaks into the vac line.

I'd check the manual transfer valve on the dash. They have a tendency to go bad after awhile. Cause 1000 different symptoms, and be the last thing checked/replaced. It's probably the cheapest place to start. The pump under the driver's feet is usually the last one to go in my experience, but the secondary culprit is normally the main pump in the rear tank.

Next time it tries to stall, toggle the fuel switch and see what happens. Same with a hard start. Back and forth a few times quickly.

Hope this helps.