sonsF150

My son and I have been fighting an issue with his 2007 F150 STX 4.6L for several months now. The car will start but it takes at least 30 sec. to a minute for it to run smoothly and it will stall if you put it in drive or reverse and take off without waiting at least 30 sec. The truck has 125K miles on it. I tried cleaning the injectors but that did little to help. It does run a little better. My belief is that there isn't enough fuel pressure at start-up and it takes some time for the pressure to build up. I can't find a pressure test connection to connect to for verification of this. I assume the fuel pump is working OK or the truck wouldn't run at all. Does the fuel pump come on immediately when the key is turned to start? Could a bad fuel filter cause this? The truck seems to run fine after start-up. This situation only happens after the truck sits for about six hours. Anyone have any experience with this or any suggestions?

sonsF150

Forgot to mention that we thoroughly cleaned the throttle body and the MAF sensor with the proper fluids. The air filter is a new K&N. The truck does not throw any codes.

weadjust

Check the fuel pump driver module above the spare tire. Read the linked thread for photos and additional info.

https://www.f150forum.com/f4/fuel-pu...-yours-152908/

powerranger262

^ This. Go ahead and change the fuel filter as well.

jshillin

iTrader: (1)

Change the fuel filter first. That's a cheap, simple fix. I had the harder start and rough idle when I first got my truck also.

I had good luck with smoothing out my 4.6 idle after THOROUGHLY cleaning the throttle body and MAF, changing the spark plugs, changing the fuel filter, filling up 1 tank with 93 octane and 2 containers of Techron. I did one of them at a time and each helped a decent amount, but it didn't fix it until I did them all.

sonsF150

I will try the following in order and report back:


1. replace fuel filter
2. run a tank of 93 octane fuel with Techron (2 containers)
3. replace FPDM (I heard this thing is prone to failure anyway)


The throttle body, plugs, and MAF sensor have already been done.


I was thinking about buying a new 2015 F150 Crew Cab to replace my 2005 Sequoia with 170K on the clock. It is my tow vehicle and my wife's daily driver. After the problems with my sons F150 I am a little scared.


Thanks ALL for the good advice!!

sonsF150

Today I replaced the fuel filter and boy did that make a big difference. The junk and water that came out of the old one was surprising. I don't know how gas was even getting through. I went ahead and put 20 oz. of Techron in the tank and filled it up with 93 octane. Tomorrow morning we will see how she fires up and takes off after sitting overnight. Thanks again for everyone's advice.

jshillin

iTrader: (1)

Mine was nasty when I changed it too. Hopefully that does it for you. The 4.6 is pretty rock solid and should be good for a long time with simple maintenance. With that many miles I'd go ahead and change the plugs if you haven't already though. The 4.6 has normal spark plugs so it's not bad at all to change.

powerranger262

Glad it's running better, hope it works out.

sonsF150

Well we didn't have to wait until morning to get results. My son went out to the grocery and called me to tell me it still tries to stall after sitting for 4 hours. I am at a loss as to what could be causing this. Could a bad temp sensor be the culprit? I had that happen once on a Saturn. The idle air control is part of the electronic throttle on this engine I wonder if that could be the problem. Any more advice would be appreciated. Again the problem is that the car tries to stall after sitting for several hours when it is first started. It will idle just fine but if you put it in gear and try to give it gas it either stalls or tries to do so. After about a minute or so you can get it to go.