After i looked at the lines that i took off there arent any check valves in the lines from the solenoid to the wheels, and then i got to thinking that if there were then the vacuum would not be able to release to engage the 4wd. Im just waiting for my epoxy to set up on the vacuum box that im fixing, i also had the dealership order me a new one just in case i can get this one to hold vacuum.

 

I checked my factory manuals and they don't have vacuum diagrams, I assume they're in a seperate book. You'll just need to trace the line and see what's what. If you ran the line direct to the IWE's they will lose vacuum as the engine creates less vacuum and they will start to engage. That will not work to control the vacuum staying constant to the IWE. You'll need to fix whatever is damaged in the vacuum system.

 

Good to know. I haven't looked but heard someone on here say there was.

Let us know how it turns out.

 

Ok i expoxied the vacuum box back together and it holds 20 psi. I put it all back together and took it for a ride. It was much better. I only had the whine noise of the actuators once. As i watched the vacuum guage in the cab that i ran a long peice of hose from a T i put in the solenoid to wheel line, i could see as the engine went higher in RPMs and under load the vacuum would go down. At the point where i got the whine, i went from a dead stop and up a constant incline. Thats the only time i got it, but the vacuum fluctuated alot during the entire drive so here is my question now.

There is a check valve in the line coming off the intake, that line T's off and one end goes to the vacuum box and the other to the solenoid. If that check valve isnt closing completely will i see the constant change in vacuum from the engine. If so then if it was working correctly wouldnt it let the vacuum box build up with vacuum as with the lines to the wheel and hold that vacuum unless the the engine vacuum increased or there was a break in the system from the check valve to the wheels? Because here is what i found.

I pulled the check valve and sucked on the ends (keep it clean guys). The vacuum side i could freely pull air through. The other side i could still suck air but it was restrictive. I had another check valve in my tool box but the wrong size. When i sucked on that one i could freely pull air through one and not the other at all. This leads me to beleive that the check valve is only partially working and im seeing the fluctuation of the vacuum from the engine in my guage and every now and then its dipping down to the 5 lb mark and that is where i get the whine.

So now after i have fixed everything else in the vacuum system a little check valve which i beleive to be worn out is standing in my way. Do i sound like that is what is going on? This may help someone else down the road.

 

What you are describing sounds like that may be the case. I would think the check valve should hold close one direction to prevent vacuum from falling.

It very well could have been from when you blew out the lines too. If high psi air went back the wrong way in the valve that isn't designed for that much pressure, it could have damaged it.

Be careful not to drive it much in that condition, it doesn't take much to chew up the gear in the actuator when partially engaged. You could be replacing another one sooner than you might want.

 

Im going to the local NAPA in the morning for a check valve and im either going to take my connected guage with me to see when my vacuum gets low and prevent the partial engagement, or plug the line so that the are just engaged. I did blow some air through the check valve the wrong way, i probably broke it, but not sure cause that happened the same time i blew the vacuum box up. I will find out tommorow morning if the check valve is the culprit now. Thanks!

 

The dealer blew up my vacuum canister as well when they were fixing mine. I wish I was as mechanically inclined as you guys so I could have fixed mine myself. Hell....I don't even know where the vacuum canister is at.....haven't looked. Good luck getting it working.

 

I replaced the check valve, took it for a ride and it went good for the first couple miles then the vacuum dropped again and started fluctuating again, so i went home and checked the check valve, it was ok, but then i found another check valve in the same supply line but up by the solenoid, i pulled it and it was completely shot, free flowing air both ways, so i went back to the parts store and got another one, put it in and took it for a ride, it went very well vacuum stayed up and it did fluctuate a little but only a few lbs here and there, im attributing that to the equalizing of pressure in the lines and that is allowing it to drop. But when i would get on it the pressure wouldnt drop too much, maybe a half a lb. I did notice while criuising on the highway that i had a constant slow leak down in pressure, never went below 14 lbs during the couple mile stretch i was on so it didnt hurt anything. So i went home again and checked the vacuum box and it isnt completely sealed i guess, i still get a slow leak down so i put more epoxy on it and im going to try it again. Good thing i have one on order. I think that is my problem now and im pretty confident that when i get the new one all my vacuum problems will be fixed. This vacuum stuff is enough to make me want to pull my hair out!

 

I replaced the valve but it still is making that shreel sound on acceleration. I think the hubs are toast but I will be ordering the solenoid from Tasca. Is this the correct part?

"Actuator, f150, mark lt - f150 new style 2004-08, mark lt - F150 NEW STYLE 2004-08, MARK LT 04-07 $109.98 $72.59"

and I should just order two to replace since it sounds like once you replace on side the other seems to go out...

 

GEOFF, before you go throwing the expensive parts at it i would get a vacuum guage and check the vacuum at the hubs and the hoses. There are two check valves, one on the line right off the intake , and one in that same line right at the solenoid.A faulty hose or solenoid is easier and cheaper to fix than the actuators. Dont get me wrong, the actuator were easy to fix but the others are easier.

If all of this rambling helps one other person than its worth it. I think there could be some other better option for the 4WD system than a little vacuum line.

The truck drives smoother, and quieter. Its going to feel like a completely new truck. I just got the truck last June and this is my first ford truck. I always have felt like during normal acceleration that something was holding my truck back, i always had to mash the gas to get it to go on normal acceleration. But now i can attribute all that to my truck in a sense "pushing" the front tires to turn all the front driveline components. Maybe thats why it seems like my ATs are so noisy. I took them off for some regular tread. Ive also read that when the driveline locks up like this that it could decrease the gas mileage by 2-3 mpg, if that is true, i got 16 mpg on the last tank during my normal driving around, i could possibly get 18-19 driving around town with my 4.6

The more i think about it, what is the vacuum box actually doing anyway? I know it holds a reserve of vacuum, but there are two check valves in the system one on each side of the vacuum box, so what ezactly would it hurt if the box was taken out? i know i did it before and it didnt work, but that was before i found out my check valves were shot.

Im going to draw up a little vacuum line diagram to show all you guys the whole system for those who havent looked into it.

 

Here is a rough diagram of the IWE vacuum system, i also typed up a quick blurb about the system that i have come to understand.





Sorry i should have typed that blurb up on the forum instead of saving it as a picture so people could search it, maybe ill retype it.

 

Ok Here is the text.

THis is a rought layout of the IWE vacum line system. From what i can gather and understand from the vacuum system for IWEs, there are two check valves and when working correctly and without any leaks in the vacuum system they hold the vacuum to the IWEs at a constant vacuum even thoguh the vacuum will change at the intake with engine load and RPMs.

When the engein is started and running, vacuum is exerted on the entire system, unlocking the IWE actuators. When the engine is turned off or 4WD is engaged (either by floor shifter of dial selector) vacuum is released by the IWE solenoid to the actuators at the wheels. So vacuum to the actuators at the wheel unlocks the hubs for 2WD and release of vacuum by the solenoid locks them for 4WD.

When the vacuum builds when the engine is started, the vacuum from the intake via a vacuum line exerts vacuum on the entire IWE system all the way to the actuators. The first check valve locks the vacuum at the highest vacuum that is exerted from the engine from that check valve down. The vacuum box now holds that highest vacuum exerted also. The second check valve located right before the IWE solenoid holds the highest vacuum to the actuators from what has been exerted from the engine.

As you start to understand the vacuum system and series of check valves, you will see that the vacuum box that is located between the two check valves does in fact act as a reserve. When you engage the 4WD, vacuum is released by the solenoid and locks the line from the solenoid back up, the release happens from the solenoid and to the actuators. This process allows the lines and vacuum box between the two check valves to hold the current highest vacuum even though the engine vacuum is constantly changing and the vacuum from the second check valve to the actuators have been lost. When 4WD is disengaged, the solenoid is opened back up, the high vacuum from the reserve from the vacuum box is then used to then exert vacuum on the lines to the actuators unlocking the actuators no matter what the vacuum from the engine is. When this little bit of vacuum is lost in the reserve it is then rebuilt from the engine when vacuum is increased from the intake.

After saying all of that and you think about what the manual says about turning the 4WD on and off, you notice that you are supposed to activate and deactivate the 4WD while under a certain speed and while not accelerating. This ensures two things, high speed engageing and disengaging of the gears in the hubs which can cause mechanical damage does not happen. It also allows a quick window of no load and low RPMs from the engine, hence high vacuum from the engine, that will quickly replenish the high vacuum to the entire system and "locks" that vacuum between the two check valves and reserve box for the reserve, as well as from the second check valve to the actuators.

This, when working correctly without any leaks always ensures a high enough vacuum to keep the acutuators unlocked when your in 2WD, or unlocking quickly when shifting from 4WD to 2WD. A leak in one of the lines,the reserve box, or an actuator, or a faulty check valve will allow a leak down in vacumm somewhere in the system that will allow the actuators to possible try to engage or close to it when not needed while driving, giving you the grinding or whinning noise of the gears of the actuators trying to mesh together at highway speeds.

 

That would more than likely be the 4.6 because the front drive line does not turn AT ALL unless it's engaged and if it were, you would know it no question, on dry pavement.

Well, more than likely the compressed air you blew through the lines blew up the the box and one way vacuum valves and as far as the box, Ford Engineers put it there for reason and when you go removing things that are there for a reason, you end up causing other problems. Trust me, they've spent millions on R&D and if it's there, it needs to be. The box and valves were blown up at the same time and you just happen to come across and fixed them one at a time by process of elimination after wards. I'm sure they were fine until the compressed air.

Not sure who would be driving enough to notice a MPG in 4WD. You should not drive far, if at all, on dry pavement in 4WD. Non Heritage 2004 to 2008 (and no reason to think the 2009 is different) front drive-line sits idle while driving normally in 2W. The front shaft, the front diff, the front drive axles all are stationary in 2WD. So it's doubtful you'll see any MPG change that can be attributed to the front drive-line because of the way it functions.

 

Well my actuator was shot to the point where vacuum wasnt able to build in the system at all so the wheels were always locked into the half shafts, those in turn were locked into the front diff and front drive shaft, but my transfer case was in 2hi, so the 4WD wasnt engaged. But while in 2WD the truck had to in a sense push the front cause the tires would move the whole front driveline. Holding back the truck in a way, and giving me alot of extra rotating mass, you get it? I think it has been like that since i got the truck last August, but i never new any different cause it was always like that.

 

Ah, I see what you're saying...

Then yeah, you might see an increase in MPG.