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4x4 IWE SYSTEM: Vacuum leak


Old 08-06-2011, 07:04 PM
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Join Date: Nov 2005
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Exclamation 4x4 IWE SYSTEM: Vacuum leak

55,000 miles with prefect working 4x4 with original updated solenoid installed with rain hat.

I wanted to share how this came about happening and how I fixed it....so here it goes.

So yesterday out of no where I get this horrible grinding metal sound. It sounds like a trailer jack dragging on the ground or a chain link fence and since I was towing my trailer at the time I pulled over to look. Could not find anything dragging truck or trailer. Checked leaf springs, everything, nothing seemed out of place.

It made this noise about 4 or 5 more times for about 1-3 seconds at a time, pulling over each time it happened thinking WTF is going on and checking underneath. Had no choice but to get on the freeway to make it the rest of the way home. Upon getting on the freeway and under hard acceleration it made this noise for about 10 -15 seconds till I was up to speed and my foot was out of the pedal. Rest of the way home it only did it once for about a second. Got home and unhooked the trailer and went out with just the truck to see if I could reproduce the noise. That would be a YES but not for nearly as long or as frequent as with the trailer.

Mostly I could only get it to act up when going up a hill or under load then but it also did do it a few times while driving on flat ground with a light pedal.

Only then did it occur to me that it could be the IWE's trying to engage themselves. Did the search on here and found all of the good articles and write-ups on how to test the system to see if there is a vacuum leak somewhere.

Before doing that I unplug-ed the vacuum line at the solenoid that goes to the wheels, by doing this you engage the front half shafts and IWE's. You are still NOT in 4x4, it's just that your IWE's are locked in. After that and a drive, NO noise could be heard. I then knew this could be my problem somewhere in the vacuum system for 4x4.

So I went out a bought a Vacuum pump tester and had at it this morning. And using this write-up https://www.f150online.com/forums/ar...then-some.html

Tested actuators at both wheels: tested GOOD, held Vacuum
Tested the Reserve Box behind the battery: tested GOOD, held Vacuum
Tested Check valves, tested GOOD, held vacuum
Tested Lines to solenoid, tested GOOD, held vacuum
Tested lines from Solenoid to engine, tested GOOD, held Vacuum.

Everything held and tested at about 22 psi.

Then went and tested the lines from solenoid to the actuators, NO vacuum could be held.

I knew I had a leak in those lines causing my problem. I went to the auto store and bought about 8 feet of vacuum line and bypassed everything with these new lines. I also put a "T" in the line just before the solenoid so I could watch the vacuum pressure inside the cab while driving. This way if I heard the noise the gauge should drop to below 5 psi. Hooked it up and went for a drive

NO MORE NOISE. So I for sure have a crack in one of the vacuum lines between the solenoid and the actuators. It had to be small enough that it did not leak down all the time but under load it loss vacuum causing the IWE's trying to engage.

So now I have a new vacuum hose assembly on order from ford as I do not want to leave the cheap soft rubber lines in there from the auto store.

Part # is 7L3Z-7A785-A

I am leaving to go out of town next week and this was the last thing I want happening before I leave! Need less to say I was getting **** off with this! But With the GREAT write up from xjcamaro89! (thanks again!!!) I was able to test everything with no trouble and saved a TON of cash instead of bringing it into the stealer-ship.

Only question that I have was there any major damage done when the grinding was happening? 4x4 Works fine now and did before also. Goes in and out smooth.


Last edited by blackjack8900; 08-06-2011 at 07:26 PM.
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Old 08-07-2011, 07:16 AM
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Join Date: Apr 2010
Location: Alabama
Posts: 473
If the 4x4 is working OK, then probably not.
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Old 08-07-2011, 08:34 AM
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Join Date: Mar 2001
Location: Rochester, NY, USA
Posts: 3,167
Yes, the grinding sound you heard was one or both of your IWE's getting ground up. How bad is the damage? The only way to find out is to take things apart. Given the amount of work required (not all that much) to see if any damage has been done, I'd probably suggest having at least one new IWE on hand for possible installation.
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Old 08-09-2011, 06:26 PM
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Well I picked up the new Vacuum Hose this morning and changed it out. After the old one was out I saw right were my leak was coming from.

It appears that the hose came out of the protected sleeve it was in and was touching against the engine, melted a hole right in it. The size of the hole was only a little bigger then pin hole too! Happened right at the "T" in the line, along side the passenger side area. Also the protecting sleeve was deformed from the heat.

With the new Vacuum line, I noticed that it is taped with aluminum tape where I had a problem with the old one and the protecting sleeve is much better on this one with the taping, no way that the line could come out with the new one.

So a word to everyone, check your line to make sure it has not fallen out of the protecting sleeve or you will end up like me

I will attach some pictures after I take some.
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Old 08-09-2011, 08:04 PM
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As you can see old line has no taping at the split point and thus it had fallen out. Also the plastic loom is deformed from the heat.

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The split in it

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New one with double warping at the "T"

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