I have a 2008 f150, truck runs great. I have a wierd problem where sometimes when I put the key in the car acts like the battery is dead, when I turn the key the starter doesn't go at all or it gives a very weak crank. When this happens I usually shift it into neutrial and back to park one or twice and the car will start up fine. Doesn't happen that often I would say about once a week but Im worried its something that might go out completely and leave me stranded.

 

Of course your battery is highly suspect they only last 3-4 years if she's that age try a new one--- high cca .. Corrosion is the first thing I would clean up . Have the battery load tested --clean everything .
A transmission switch is not going to cause a slow crank . Put a voltmeter on battery terminals during crank ,she should not collapse .

 

Along with the starter since it is 9 years old.

 

I bought the truck used 2 years ago, im sure he must have replaced it at least once but I'll go get it load tested just to be sure. Still think somethings going on with the switch that verifies trucks in neutral

 

My 08 F150 5.4 4spd auto won't shift into any gear with key in any position.
Also ONLY get an airbag light, speedometer jumps from 10-25 mph and a light buzzing from under truck somewhere around fuel pump area...

 

Key hits starter relay thru trans sw then that triggers starter solenoid then solenoid heavy bar inside makes the connection to the main battery lead on starter. That heavy lead to battery carries the starter current not the key switch or the transmission switch etc . If she slow turns the battery is collapsing or corrosion in leads to starter bad or ground bolt on starter bad/starter bad .
Another bad thing that can happen is hydro lock . You really don't want that, it can bend your piston rods . A dripping injector is all it takes ,once the cyl has liquid fuel in it the piston can't compress a liquid . This just happened to one poster. What a mess to try and fix ,.mostly a reman motor job .
Start with a new battery high cranking amps . Then test starter if that fails . Primarily the battery is number ONE failure . Yes they cost a $100 or so every 3-4 years ,beats getting stranded. Clean every connection on battery and starter especially if you are in salt country . Its only going to get worse as the cold comes in and reduces battery power .
If you think a bad injector may be it then lay out fuel rails on dry newspaper injectors hanging off it and turn key on, none should drip, Key brings on fuel pump .Reinstall with orings coated with motor oil .

 

it must have been a problem with my transmission, had my transmission rebuilt last year and the problem hasn't occured after that.

 

I reckon best plan of action for me is to take off transmission selector switch to see if it shifts but oddly the chrome bottom you compress before shifting doesn't compress. I rocked truck while ol lady tried to shift, attempted manually under truck,
this is only oddity noticed while reading forums and trying everything suggested.
would command start module cause auto trans to not shift?

 

Mine doesn't have button . There is a shift solenoid lock that is battery operated . It won;t let you shift without brake pedal pushed . I would guess you have a problem with that
circuit .I have no idea about button type shift .

 

Resolution found.
Night before the morning truck didn't start there was a severe lightning storm.
A manufactured June 2016 battery 800cca that I charge before and after every winter which takes 6-10 hours each time was completely dead (guess the backup I used is finally worthless...a 2012).
Charged backup and truck battery about 70 days ago.
Has never went dead like this with the 2008 technology where there's never anything "accidentally left on" as all is auto.
Took a little over 48 hours to completely charge battery now truck is fine

 

They never quite recover . We used banks of them at the power company to operate vital systems . If we ran one down somehow it was a fatal flaw costing tens of thousands of dollars per bank . In an emergency we would use car batteries jumped together to get 125vdc . The commercial batteries could last 20 to 25 years and we maintained them weekly even though they were automatically charged and alarmed all cells were specific gravity tested each month .
If you must let a battery sit use a small trickle charger on it and keep them cool . Heat destroys battery's .