Crank/Hard start

Messages
482
Location
USA
99 F 150 4.6 Engine. Usually when started in the AM it cranks and starts fine, but after it sets for a few hours, it cranks fine but is hard to start. If I let off the key and try it again it fires right up. We are talking like 3 to 4 seconds. I put a fuel pressure gauge on it and it has around 5 psi key on engine off and about 30 when running.Pulling off the vacuum on the fuel pressure regulator the pressure rises maybe 7-9 psi. Regulator did not appear to have any fuel in it. When turning off engine the pressure goes down to 0 in about a minute. The fuel filter has been changed fairly recently as this problem has been ongoing for some time. The filter change did not make any difference. Revving the engine made the psi go down a couple psi at 2,000 RPM. The vehicle drives fine normally no check engine lights and has about 108,000 miles and no stalling issues. Cleaned the MAS and Throttle Body and while it was a little dirty, no help for the hard starting. What are your thoughts Fuel Pump?
 
Messages
2,440
Location
snowblind in TX
Fuel pump check valve. Usually acts up when engine sets for a few hours/overnight. Test: Cycle the ignition 2-3 times (don't crank it) to pressurize the line, then crank it up. Problem better, time for new pump.
 
Could also be a dirty relief valve that is bypassing if it is the return type. In either case, try running some good fuel system cleaner through it and see if it cleans up. Good cleaners would be Gumout Regain fuel system cleaner (the high mileage one is said to have a higher concentration of cleaners (amines), or Redline SI-1 complete fuel system cleaner. Gummout you can get at Walmart.
 

oilstudent24

Thread starter
Messages
482
Location
USA
I did try a couple fuel cleaners I think I did a double dose of techron or b44 Chemtool. No change in the symptoms.
 
Messages
2,440
Location
snowblind in TX
Originally Posted By: oilstudent24
So if the problem gets better I should replace the pump, correct?
Yup. When you get a combination of a bad check valve, and high ambient/underhood temps it magnifies the problem. Once pressure bleeds off the fuel boils in the line, and vapor replaces liquid fuel in the rails and fuel line. By cycling the key a few times the fuel pump is cycled and gasoline, liquid gasoline, is forced through the rails so the injectors don't suck vapor for those first few seconds.
 

oilstudent24

Thread starter
Messages
482
Location
USA
Ok so looking to replace Fuel pump with an OEM Motorcraft like was on it before. If I buy the Motorcraft, do I need to buy anything else like a strainer or fill hose or any assembly that is not included in the pump? Thanks
 
Messages
5,651
Location
Iowa
Fuel filter if applicable. I don't care if you had put one on it 5k miles ago... Put a new, name brand filter on it and keep the receipt with mileage on it. On the rare instance of a pump failure, some stores may get a bit grumpy if you can't prove you replaced the filter when you go to talk to them about warranty.
 
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