Casey Booth

Hey guys,

New to the forum!

Ok, I need some help here.

My truck died the other day at an intersection, I started it up rpms rose then dropped and it died (almost immediately). Also right before it died, the brakes felt hard to push, steering was fine.

Short background, the truck has been missing and having slow acceleration for a few weeks. Replaced coils and plugs and it ran a little better but not much. CEL was still on, pulled codes and got p0161, p0171, p0174 (i think), and another one for PCV valve.

Replaced PCV valve and MAF sensor, still ran the same. Thought maybe I had/have a vacuum leak, but cant tell from where. Also thought maybe brake booster just because of the brakes.

Thanks guys!

2007 F150 SLT 4.6L V8 - 2wd 4 door - Stock - ~170K mi

nrivera04

Welcome. Can you also include your year and engine in future posts?

Have you ever dropped your spare and inspected your FPDM? You're describing common symptoms with a failing FPDM.

Fuel Pump Driving Module.

Casey Booth

Ok right on, I'll check that out. And the truck I'm talking about is the one listed in my signature.

Thanks!

nrivera04

10-4. I do most of my browsing on my phone and don't see signatures when using the mobile site. Let us know what it looks like. It'll will likely be severely corroded, possibly even broken if it's never been changed.

Casey Booth

Update: I checked the FPDM, it looked fine. I didn't think of this before, but I disconnected the MAF sensor and the truck starts and runs, but runs terribly, worse than before; erratic idle, misfire, and I can hear a popping sound from the engine. I'm assuming all of that's because the MAF is unplugged.?? maybe, idk.
That said it dies if the MAF is plugged in. I put a new MAF on as well and the same issue. Maybe I bought a bad MAF sensor. I'm trying to avoid taking this thing to a shop lol.

redfishtd

If so change it, as it will go bad if not upgraded . This module creates this problem frequently. It would be high on my list if I were you . Dorman should be fine .

redfishtd

maybe a vacuum leak ? Maf unplugged, the pcm will compensate and plug its own values in . you tube Homemade smoke machine maybe the answer . Sensors can be bad but usually its like shooting the messenger .Unbalanced air intake can be caused by vacuum leak or air leaks bypassing maf .
PCM is throttling injectors and changing fuel delivery because it is confused by the amount of air entering system .
If it thinks not much air-- its going to cut back fuel .
P0161 trouble code identifies that there is a problem with the heater control circuit in the bank 2 sensor 2 oxygen sensor. ' Fix this '
P0171 OBD-II Trouble Code: System Too Lean (Bank 1) too much air
P0174 OBD-II Trouble Code: System Too Lean (Bank 2 ...too much air
Hard pedal caused by low vacuum .
O2 sensor heater will affect this lean condition
You changed pcv valve ? my 05 is in the drivers side valve cover have to replace cover .
Vacuum leak high on my list-- o2 sensor in trouble

badtoys

Unplug maf sensor and see if it runs if so replace

Tommy Marquez

Ok when you push the brakes they got hard. Sound like a bad brake booster. This is what your master cylinder bolts to. You have a internal vacuum leak in the booster and thats why you have p0171 p0174 lean codes. What I want you to do is unplug the large vacuum line to the booster. After that plug the vacuum line with something maybe duct tape to block the line. Start it up and see how she runs. Seen it many times brake boosters do this in my line of work as a auto tech. What gives it away is your brake pedal got hard and lean codes. Unmetered air from booster. The diaphragm breaks and cause a huge internal vacuum leak which would cause your truck to start and die.

badtoys

just changed maf runs great