ErikP

hello guys, new to the forum, but figured I'd join and learn what I can as I've bought my first F-150.

anyways, I have a 2006 Ford F-150 XLT crew cab, with the 5.4l, 4wd too. Last year when driving on the dirt road I had a stick kick up and completely kill the truck. I got out and seen the stick wedged in between the harness connectors on the ouside of the frame rail behind the drivers side wheel. It was wedged in there pretty good, broke some Christmas tree clips, but once I pulled the stick out the truck fired right up and drove fine.

Ever since that day, I've had random events where I go to start my truck and it won't fire. It cranks and turns over just fine, but won't fire up and run. No matter how long I turn the key.

Heres the thing, if I get out and wiggle the connectors on the frame rail, the truck will fire right up again. It's done this probably 6-8 times in the last 8 months, and every time I have gotten it running right away by wiggling those connectors.

The truck never stalls. Not even once has it. It runs good, smooth idle when warm (usually slightly rough when cold) but drives good.... no problems. Just periodically won't fire up.

Obviously something is up with the connector, but there's a few things that get me..

it never stalls, just won't restart. I think it's only happened after it's been running however.

It fires right up, with no sputtering, so i don't believe it's firing the injectors. It doesn't sputter when cranking either, doesn't even try to fire during the no start event.

Connectors look good, but I can't seem to figure it out. Based on the info provided, does anyone have any clue or insight as to what it could be?

Thanks in advance!
Erik.

redfishtd

I don't have a handle on the wiring harness you are talking about . I'm going to do some guessing .
Pcm is on passenger side on firewall up high . Engine harness on top of engine , injector harness ,cop harness, cam sensors crank ,sensors .
The main fuse panel is passenger side kick plate .
I'm guessing the circuit running to the rear that would shut down truck would be fuel control . The pressure sensor on fuel rail(drivers side) sends a signal to the Fuel pressure demand module on rear axle . FPDM is a problematic device because its alum sets on steel axle and electrolysis eats it up .
This module starts the fuel pump whenever rail pressure needs it . This system no longer pumps back into tank like the old systems .
So it coincides with your guess of a fuel problem . I have replaced my FPDM with the new type on stand offs . FPDM symptoms are similar to your failure .
I haven't looked at my connectors yet . You could spray out connectors with contact cleaner . Its even possible that the stick stretched wires and started to break them inside of the insulation . I' m afraid its hard to trouble shoot the loss of signal once you disturb connectors . You will have to have diagram ready to go and a meter with sharp pins to pierce insulation to see where you lose signal .
Transmission wires are near there too so ,I'm just guessing . Ill think about it .

ErikP

I know the FPDM is a common problem, but would that not simulate a dead fuel pump? I kind of ruled that out because wiggling the connectors fired up the truck.

As for the connectors, they are right below the drivers door on the outside of the frame rail. 3 big huge connectors that have a plastic shroud around them, normally protecting them from road debris.

What gets me is it never stalls the truck, only prevents it from firing up again. It sees weird that it can kill fuel when cranking, but will never kill fuel and stall the engine. I'm honestly kind of stumped.

techrep

iTrader: (1)

Have you tried to tape them up ? You said it broke some retainers

redfishtd

It is just similar type and area of your problem . Mine drove me nuts every few miles it would shut down after I put a new one on ,gasket in connector was the problem .
Some guys can't get them to start at all with that problem .
An electrical intermittent drives the shops crazy . It has to quit when they are working on it .
My guess is the fuel sensor on rail tells pump module to shutoff as long as truck is running high fuel pressure is relieved by injector drain but when you shut it off if the low pressure signal intermittent broken it will not start because its not pumping up till you wiggle wires so both wires could be in trouble . But I really don't know .





Well it looks like Injector pressure sensor works thru PCM to drive FPDM

ErikP

Hey, thanks for the response Redfish. I think you might be onto something. I suppose if something was killing the pump momentarily the engine could still run. That is as long as the pump comes back before the fuel rail pressure gets too low.

If thats the case, I could be turning the truck off the exact moment the pump is not running (for whatever the unknown reason, if that is what actually is going on). which would leave me with a no start condition next time i attempt to fire it up.

Anyone have any good ideas or methods for ensuring i didnt damage a connector pin or damage the wire under the insulation?

redfishtd

The fuel pressure sensor on fuel rail goes to the PCM it controls the FPDM module ,I had wrongly assumed it went directly to FPDM .The power to the fpdm comes from Pcm controlled fuel relay then thru the crash inertia switch to pin 5 of fpdm . It gets is grd from the frame near the fpdm . So just in case clean that grd .
Get a meter on that pin 5 and wiggle those connectors Pins 1 and 6 are the FPDM drv cir from pcm . So put a voltmeter between 1 and 6 and measure that signal and wiggle . I had to hand draw this all out ,it goes thru so many drawings . Put the colors and everything on your drawing and start trying to break it .
You must find out where you are losing it even if you have to tie wires into voltmeter inside the truck until it breaks til you find the right lost signal .
If you can't find it maybe you could get the torque pro setup with android phone using a bluetooth code reader . I have one but f150t is your man as I haven't got used mine yet .