In the midst of putting my PIE adapter in today, I noticed a wire that looks out of place. While putting my negative battery cable back on, my dad and I noticed a red wire within black wire looming just sitting there. It looks as though the end of it is capped off, meaning that it doesn't have any real connection to make. I followed it around to the other side of the engine bay, and it plugs into something near the valve cover on the driver side.

Any ideas on what this "capped" wire might be? I hope someone else has come across the same thing under their hood. I've got the 5.4 V-8 in an XLT SuperCab. Below is a pic of what I'm talking about.


Below is the wire on the driver side (in the red circle) that is the same (I think) as the unconnected one the passenger side and where it connects (to what, I don't know).


Hope ya'll see what I mean.

-Travis

 

Is that black box bolted to the fuel rail? Does it hook to the fuel rail like it senses pressure or something? You got me.........

 

in my truck that wire is not disconected. it is connected to a black wire that goes arround behind the battery. I couldn't see where it goes after that because I would have to pull the battery to see. I am upplodeing a pic right now and will post it when it gets done uploading.

 

hers a pic

 

Well I'm not sure what the wire is for but I do know that if Rock sees all these filthy engine compartments there will be Hell to pay.

 

That's for the extra 200HP flux capacitor, didn't you know?

 

I wanted to know what that was to. So I took it to the Ford dealer to ask them what the heck it was while I was getting the oil changed. The tech looked at it, seen that it went into the cab thru the firewall, pulled the plug off the end of it and said that it was a vacuum line for some option that I don't have. He didn't know exactly what it was for, but he said that it was a vacuum line of some sort.

Maybe it's for the extra 100hp I didn't order!

 

Jakazz says a tech told him it was a vaccuum line, and i see that jasonkola has it, and it's connected. Could this be for the Electronic 4x4-on-the-fly? That would make sense to me.

-Travis

 

It's not a wire, it's a vacuum line. I believe it runs to the charcoal canister seeing as it starts at the fuel rail. There's a TSB about rough idle/stalling that may have something to do with that line. I think they disconnect and plug it to prevent excess fuel vapor from entering the engine and stalling it. If you've been to your dealer recently they may have done this to prevent a possible problem down the road.

 

now I am thinking of disconecting it and plugging it. I wont though unless I figure out what it is really for. I should ask the dealer next time I am in there. I bet someone on here has a service manual that will tell us what it goes to. I might just go out tomorrow and pull my battery so I can track that thing and see where it goes. you got me curious now.

 

That's not how the charcoal canister works though.....The line from the charcoal canister gets vented into the intake manifold when the purge valve activates at certain RPM/load conditions. And the charcoal canister is fed from the gas tank vapors. It shouldn't tie into the the high pressure fuel at the rail in any way. I just checked on my truck and I have that sensor looking thing on the fuel rail with a big rubber vac line running off of it going into the rest of the vacuum system for the brake booster and back around to the intake manifold, but I don't have that little red line running over there by the PCM. My only guess is that sensor is possibly a pressure sensor for the rail pressure, but I don't see why there is a vacuum line on it. A typical fuel pressure regulator that sits at the end of the rail and returns fuel to the tank would have a vac line on it to control the pressure BUT our trucks seem to use a returnless rail system and there is no way this little sensor would control pressure with that vac line being where it is located on the rail.

 

I'll let it go... but just this once.

 

The vapours are purged when the canister gets a vacuum signal that is sent under certain conditions.

 

well dose any one know for sure what that vacuum line is for. so far I have heard alot of ideas. it dosn't make any sense that mine is conected and every one elses is disconected. dose any one else have a fx4 and have it disconected. I was too lazy today to go out and pull my battery and trace it. that and it was cold out today. I think it only got up to 60 F. here today. makes me realize winter is just arround the corner.

 

I have a Fx4 and mine is also connected. Dont' have a clue what its for but its there.