Hi to all, got a noob question here. I just bought a 2008 f250 6.4 Diesel last month. It needs a thermostat. Im pretty sure it actually dosnt have one in it at all but this is another story. So it goes in tomorow to have one put in and coolant service done. Anyway the point of all this is while the service tech was looking around under the hood he noticed what he called a vaccume pump unplugged. Its an electric pump mounted on the left fender in front of the master cylinder, after plugging it in it started running and then he noticed an additional length of vaccume hose (About 8" long) attached with a tee adapter and a missing hose from that tee, we could not find the missing hose. He said he has never seen this modified this way and could not speculate to why it was done. i removed the extra length and connected the original hose to the pump and left the electric plug installed. The tech said the pump should stop running eventually and only turn on when it was needed. When i got home from there i left the ENG run and popped the hood, the pump was still running, and after about 5 min it still hasnt stopped, so i turned off the ignition. Can anyone tell me more about what this pump is, and how its supposed to operate, and what the modification could have been, and what leaving it unplugged would do to the truck? It has no trouble codes or loss of obvious performance so there is no help there. Thanks in advance, Mark

 

Would be used to operate the front hubs if you have ESOF. Shift on the fly.

If you have the switch inside to put it in 4x4 then the vacumn pump operates and turns the hubs to lock the front end in.

So look at that and also look at your hubs. Do you have aftermarket hubs up front?

 

I have original hubs, They are like all the others I have seen on same model trucks. They say Lock the 1/4 turn away Auto, they are currently in auto btw. Thank you for the answer, but can you speculate to why it was modified with another hose spliced in to it? and also why does the pump continually run? If I had to venture a guess I would guess checking for a cracked or broken vaccum line from the pump down to the hubs, or maybe the 4x4 switch is shorted asking the hubs to lock, which may make sence as to why it was left unpluged by the previous owner, Thanx, Mark

 

I would suppose it does not work so he unplugged it and then just manually operated the hubs.

 

ok if something didnt work why bother disconecting? If something worked when not requested (without turning the switch) then i can see disconecting. My pump runs continuously when the switch is in 2H
Now as a follow up question, in a functioning system, will this pump continualy run when the switch is turned to 4H/4L? Or will it build up vaccum then cut off and only turn back on if vaccum is lost.
Now another follow up, Does anyone have a speculation as to why it was modified with a tee for another vaccum line. like i stated in the org post, i cant find a loose vaccum line to trace back to a mod.

 

This should work both the hubs and the heater therefore the tee. And yes when it draws a vacuum it should shut itself off.

Mark

 

ok thanks, so now i need to look for the missing vaccume hose before PA winter sets in. Thanks for the help

 

Yep, because you've probably only have defrost (the tee is for one going to the 4x4 solenoid, one going to the HVAC).

 

Hi all, thanks for the help, but.... I unplugged it (electric plug, and vac hose) and the heater and ac work normally, when i switch the **** between deff, deff/floor, floor, panel/floor, and dash vents, they all change normally. Now its all normal except for the heat temp, which is not hot, but thats part of the can of worms that got me to the vac pump to begin with. Im taking it to the shop tomorow morning to get the thermostat replaced so i will drive the tech nuts with all these questions and see what it ends up as, thanx, Mark