Howdy all.
I've got a 2004 F150 XLT, Screw with the 4.6 2V and 4x4.
I've had it for a couple of years and have been steadily replacing things as they wear out (~160,000 miles).

Last winter, I started getting this terrible noise under sustained load. It comes from the front passenger side of the truck, and sounds like rocks shaking in a tin can, or a metal rattle snake. It builds up in volume, then dies off over 1-3 seconds. When going up a steady incline, I can almost turn it on/off based on throttle position.

With the windows open, it's pretty loud and sounds like it's under the truck. With the windows up, it sounds like under the passenger footwell. Doesn't really happen in the Summer, but anytime there is a steady incline and it's cold outside, it comes back. Doesn't happen just revving, usually only when driving around 50mph.

I've already changed the IWE solenoid at the firewall, and the IWE actuator at the front passenger side. I thought it sounded like a heatshield, but they're tight and the only spot close to tapping on a fuel line I bent to get more clearance.

It really sounds awful, and it's starting to concern me. Engine and transmission sound/feel fine, but it's a concerning noise.
I appreciate any help.


SOLVED: The 4x4 check valve was faulty and allowing air flow in both directions (easy to check, just remove it and try blowing air in both directions). This meant that under load, when vacuum dropped in the engine, the vacuum in the 4x4 system also dropped (this is supposed to be prevented by the check valve). So suddenly, the 4x4 wheel ends were trying to engage, causing the terrible noise until vacuum came back. Maybe the cold weather causes the check valve to act up more, not sure.

There is a Ford part available to replace it, but I used "Dorman 926-465 4WD Actuator Vacuum Check Valve" since I could get it much sooner. Very easy install, just have to remove the battery to access the connections under the passenger-side firewall-mounted solenoid. Be careful not to damage any of the vacuum lines, they may be brittle.

 

I have the same style truck: 2004 XL 4.6L with 195,000 miles on it. Read your other post and can appreciate all the work you have done on you truck to keep it running.

You may want to look at the IWE's one more time. Use a vacuum pump connected directly to the IWE and see if they both will hold vacuum. I had the noise on the driver's side, because of the IWE not engaging all the way because the passenger side IWE was leaking vacuum. I replaced the passenger side IWE and the problem was resolved.

IWE's are normally disengaged in 2X mode by vacuum being applied to IWE. When placed in 4X mode the vacuum is removed and the IWE engage. If vacuum is reduced by a leak, then the IWE isn't able to fully engage or disengage and makes the noise. You will only hear it when the wheel and axle aren't at the same speed (under load).

You had mentioned, in your other post, that you could get IWE that kept the hubs locked. I wouldn't recommend this, as it will affect your gas mileage! I will guess, if your drivers side IWE is currently engaged all the time, if you correct it, you will see an increase in MPG's!

 

Hey, thanks for the reply and for looking at my other post.
I just ordered a hand vacuum pump to test the driver side IWE actuator. I haven't looked at the lines yet, but I'll give those an inspection as well too.

Interesting you mentioned MPG, I did notice at my last fill-up that my MPG had significantly dropped...

Losing vacuum under throttle makes me wonder if my check valve is bad. Seems like that's a cheap fix if so.

 

SOLVED: The 4x4 check valve was faulty and allowing air flow in both directions (easy to check, just remove it and try blowing air in both directions). This meant that under load, when vacuum dropped in the engine, the vacuum in the 4x4 system also dropped (this is supposed to be prevented by the check valve). So suddenly, the 4x4 wheel ends were trying to engage, causing the terrible noise until vacuum came back. Maybe the cold weather causes the check valve to act up more, not sure.

There is a Ford part available to replace it, but I used "Dorman 926-465 4WD Actuator Vacuum Check Valve" since I could get it much sooner. Very easy install, just have to remove the battery to access the connections under the passenger-side firewall-mounted solenoid. Be careful not to damage any of the vacuum lines, they may be brittle.

 

What is IWE?

Jim

 

IWE is the integrated wheel end, the portion that lock the front half shafts to the wheel hub. Actuated by vacuum, they're responsible for 4WD

 

Thank you.

Jim