Hi everyone My 2007 4.0 has been giving me headaches for a while; for months now she just does not want to fire up after being parked for more than 5 hours. It does not matter if I prime the fuel pump once or three times, she takes a lot of cranking be fore she starts. Once she does she runs rough for about 30 seconds or so and then goes into normal, smooth idle. Tapping the gas pedal during the rough idle period will cause the engine to stall and shut off. Once she runs, she runs great; no stalling, no hesitation, great throttle response. The weird thing is that this problem only occurs when the ambient temperature is above ~40F. Below that she fires right up, no hesitation at all. She also starts right up if the engine is still warm after the truck has been parked for an hour or two, no matter what the outside temp is. No check-engine light, no codes; I have changed the fuel pump twice, the fuel filter multiple times. Replaced the spark plugs, and did not notice a fuel smell when I took the old ones out. Also no fuel contamination in the engine oil, so no injector stuck open? One thing I did notice is that while the fuel pressure is where it should be while the engine is running it drops to below 20psi within 15 minutes once I turn the engine off. But it does this no matter what the ambient temperature is, and I have never noticed a fuel smell anywhere around the truck, so I don't think there's a leak. Most people report issues starting their truck when it's cold outside, for me it's the opposite and that really throws me for a loop. I don't want to take the truck to a shop because I am worried they will replace half of everything before they find the actual issue and meantime I am out a ton of $$. Trust issues... Does anyone have any suggestions what i could try next? Thanks, Pauline Anna
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Could be a leaky fuel pressure regulator, or a weak fuel pump check valve. When the engine is off, the fuel pressure should remain fairly constant. If it bleeds down quickly, it could be either of those. When it's cold, the fuel doesn't vaporize as easily, so it might be easier to start. When it's warm, the fuel vaporizes, and with low fuel pressure, it takes longer to crank. Just a thought.
Hi DragonQuester, Thank you for your response. I thought that on 2007 Rangers the FPR is part of the pump? Meineke changed that twice without fixing the problem, and I replaced the pump a third time with a MotorCraft pump. Not saying it's impossible, but what are the chances of getting three bad replacement pumps in a row?? I have no idea where a check valve would be, could it also be part of the pump? The evaporation theory makes sense, but I have not yet found a leak through which the fuel vapors could escape.
