I have a 2005 f150 fx4 that has a intercooled roushcharger on it. I have a boost gauge hooked up and it sits at -18 idling and goes to 0 when I open it up. What could be the problem?

 

Where do you have the boost gauge connected? It should be connected to the same line that goes to the fuel rail sensor.

This is the vacuum harness that you tap into.

and it plugs ino the vacuum port to the right of the intercooler tubes.

 

I believe that's the one I hooked it to. It's on the passenger side it has a vaccum line on it and a nipple that has a rubber cap on. I pulled the cap off and hooked my line to that.

 

So to clear it up is the truck boosting and it's a gauge issue or is it not and it's a missing boost issue? The foot & ear gauge should tell you if you have boost.

 

The gauge is brand new. It whines but doesn't pull any harder then stock....

 

You need to validate your bypass valve is working then.

When vac is < 0 it should be open, but when it hits 0 it should close and thats when the boost is introduced.

If your valve is stuck open then you won't see boost and you pretty much have stock preformance.

I can't tell you where it is on a roush, but someone will chime in or you can search for it.

 

Is this a new install or a new problem? There are a couple of scenarios I can see that would prevent the boost by-pass from closing. First would be no vacuum source or your vacuum source has a leak. Second is the by-pass needs to be adjusted because it doesn't allow the valve to close when vacuum drops to zero. The vacuum motor is mounted to the supercharger on a slotted bracket to allow adjustment. If the bolts backed off or the bracket slipped out of place, you probably won't be able to build boost or at least full boost.

My suggestion would be to study your instructions and check the vacuum routing. On a new install, you might not have routed the vacuum lines properly with the boost control solenoid. You should be able to push the linkage on the vacuum motor with your finger and when you let it loose, you should be able to hear it snap shut, which means the butterfly valve is closing. Unless the valve is closed, you can't make boost. Also try moving the vacuum motor it to see if it's loose. The vacuum motor is located at the rear and base of the supercharger the driver's side.

 

If it is on the passenger side then that is probably the wrong hose. you need to double check and make sure it is coming of the intake and not the plenum where the throttle body is bolted to. the hose assembly is on the driver side rear to the fuel rail sensor on the driverside. If you can take a picture of where you have it hooked up that can help us out.

 

Mine runs to a port on the passenger side too.

 

I had it hooked to the plenum. So it wa hooked up wrong. I hooked it to the hose on the manifold and it boosts 4 lbs.