This has been goin on for a little bit now and it is progressivly getting worse. I have a 99 f150 with a 5.4 with 136,000 miles on it. Lately it takes more and more cranking to start it up. Once it starts it runs perfect and as long as it is warm is starts fine. Its only when its cold that it has trouble starting. Also my gas mileage seems that it has been getting worse. Is this a fuel pump goin bad or is it something else????

 

I don't think the cranking problem is related to the gas mileage problem. Although, it could be related if your plugs are going.

The fuel pump has a "check valve' in it. What that does is keep the fuel that has alread been pumped to the injectors under pressure. If that goes then the fuel will leak back into the tank. That will cause longer than normal cranking times because it takes a few seconds for the pump to get fuel back to the injectors.

First question I have for you is does it only take a long time to crank after the truck has been sitting for a few hours? If so then next time you go start it after it has been sitting, turn the key on, wait about 5 seconds then turn it off. Do that a few times before you try cranking it. What that does is cycle the pump. If you listen carefully when you first turn the key on you will here the pump kick on then shut off after a few seconds. By letting the pump cycle a few times it allows it time to get fuel to the injectors. If it starts right up after doing that then that is a real good sign the check valve is going. Since the check valve is part of the pump you replace the entire pump.

 

Could be a leaking diaphram in the fuel pressure regulator too. That would explain the poor milage. If it's leaking you are getting extra fuel back through the vacuum line into the intake manifold. And when it sits under warm conditions, the fuel is leaking out into that vacuum hose as well causing the loss in fuel pressure and the extended crank. Try pulling the vacuum hose off of the regulator(located on the driver's side of the engine i believe on the fuel rail...looks like a little UFO with a vacuum hose on it). Watch it with the motor running for about 5 min and watch for any signs of fuel leaking out of the top.

 

Ya it only does it when its been sitting a while. But it doesnt do it every single time. This morning it started up fine, but the morning before that it took it a while.

 

the pressure regulator would be a great place to start, its under the hood, so just pull off the vacuum hose and it should be dry, if there is fuel or moisture there repace it.

You could buy a fuel pressure tester as well, you can get one for around 50 bucks since they all use common valves now. It will pay for itself in the long run.

 

You may need to wait a while after you pull the vacuum hose off. It won't always be leaking right away. Wait 5 min or so and watch for leaking out of the regulator.