Clifford the F-150

last month I screwed around and took my truck threw some mud. I ruined my alternator. Had to be jumped two or three times on the way to Autozone. I replaced the alternator. It is one month later now and my truck kept sounding worse and worse when i tried to start it. The battery was dead. Yesterday I went and bought a $150 Duralast Gold 700 Cold Crank Amp and 875 cranking amps at 32 degrees F. My old battery was 800 Cold Crank and 1000 cranking amps at 32 degrees F. I don't know much about batteries but Autozone assured me this one would work.

Here is the problem. I put the new battery in and got in to go to work. I got to the end of the street and it died. It died 3 times on the way to work. I had to keep one foot on the brake at all times to keep giving it gas so it wouldnt die. it drives fine it just wont idle. If I let off the gas it falls to 200 or 300 RPM and just bounces until it dies. PLEASE HELP!!!

Martian

Pull the battery out and charge it externally at least overnight. Put it back in and start the truck. Disconnect the battery after you start the truck. If the truck dies, it's not the battery. It's not receiving power from the alternator somewhere along the lines.

Martian

Did you clean off everything when you were done mudding? MAF sensor, check the air filter, throttle body, all that? Check / replace your FPDM, too. You might have gotten water on it. It's famous for having a crack and then shorting out when water hits it.

Clifford the F-150

What is fpdm

tcp2

Never disconnect the battery from a running truck. The battery is sinking the voltage peaks from the sine wave signal from the alternator. When you see 14.3 V output, that is an RMS value and without the battery attached you can see peaks of 20.2 volts that are not sunk into the battery. Your computer won't like that.
Try disconnecting the battery again and following the re-learn procedure exactly.
See here:

https://www.f150forum.com/f2/new-bat...roblems-50511/

Martian

Oookay... scratch that then... even though it's never given me a problem in any vehicle.

Anyway the FPDM is your fuel pump driver module. It is mounted above the spare tire on the frame rail. Ford had the brilliant idea of taking two dissimilar metals and having them contact each other, which made the FPDM housing corrode and crumble. It's been a hell of a problem with these trucks as when it breaks, it lets in water and all other sorts of nastiness that kills it, and then you're left stranded because there's nothing powering your fuel pump when the FPDM dies.

Clifford the F-150

Thank you so much this was the problem

jake_85

Yessss the relearn procedure works wonders. I had slightly rough idle, but its about time for plugs so i assumed it was thatthat, did the relearn for ****s n gigs, idles now without skipping a beat. Seems to accelerate more smoothly also, that could just be in my head though haha

Jamesnygren03

I would like to chime in for all future people. 2012 F-150 5.0L. I replaced my steering rack and programmed myself. As per the huge F-150 maintenance manual that floats around this forum, it called to disconnect battery. I did so, and when everything was done the truck ran horrible. I mean everytime I came to a stop it would stall. It was like it was getting choked out of air. I bought some throttle body cleaner, removed the throttle body from the truck, and also the brass flapper from the throttle body to completely clean. Reinstalled the components and the truck ran like a dream. I would assume like everyone else has said, the truck air/fuel adjusted according to the throttle body getting more and more clogged. A simple clean and were running amazing.

Thanks everyone for all the input, saved my bacon!