My 1996 F150 XL auto with 5.0 has had a difficult to explain starting issue ever since I've had the truck. When it sits for a couple hours and I turn the key to start it, it will immediately sputter and act like it is about to get running and then dies. I then have to start over by turning the key again and it cranks for about 4-5 seconds and does what I call "sputters to life." Once it sputters for the first couple seconds it then runs and idles great. It has 332k miles and this could be the result of a old tired engine because it typically lets out a nice puff of smoke from the tailpipes from what I think are leaky valve seals after sitting for a few hours but the smoke immediately clears up. When the truck sits overnight and i start it the next morning to go to work it always starts right up first try without any issues. It appears to only crank for the 4-5 seconds after it sits for a few hours. When its warm and i make multiple stops when running errands it also starts right up the first try.

I ran the codes using an OBD2 scanner and have codes:
P0401 -EGR insufficient flow
P0171 -bank 1 lean
P0174 -bank 2 lean

I have since gone through some routine maintenance after buying the truck. I have changed the spark plugs, fixed a vacuum leak where the vacuum line connects to the fresh air door flap, removed the MAF sensor and cleaned with MAF sensor cleaner, and changed the PCV valve. I'm wondering if a have a leaky injector or if the the EGR is allowing exhaust gases to enter the combustion chamber at startup. Could a rich scenario be the actual cause for the smoke at startup? I replaced both fuel pumps because the rear pump did not work when i bought it but that did not change anything with the intermittent starting issue. The truck has also been averaging about 8 mpg. Sorry for the long post but hope there are some suggestions for me to check into before changing any parts

 

This is my best guess with this info. The lean banks could mean the H2O sensors are bad and not sending information to the PCM (computer). The PCM thinks the truck is running lean and is adding fuel to compensate for the incorrect fuel/air ratio. This is probably why you are getting such poor mileage also. So I would think basically the condition is excessive fuel being added by the PCM causing the issue and over time evaporates and lets it start when it can or cools. I would think the puff of smoke when starting helps confirm this especially just on start up. The H2O sensors need to be changed periodically and with your mileage who knows if/when it was done. If you ran codes without the engine at operating temp either Key on or Key off you could get the EGR code and I wouldn't be to concerned about that at this time. Sandy