I don't want you guys to get the wrong impression. I bought my 01 Ram in December 07 and like it much better than the F150 I drove for 6 years. Ihave worked through a few issues but this one is a pest. When accelerating to pass someone on a highway, I noticed that the air will blow through the vents when my HVAC controls are off. Both check valves have been replaced and I checked the vacuum lines under the hood. Are there any other lines I should check? BTW, I noticed when I filled the gas tank recently there is no vacuum when I release the cap. I am not sure if these two items are related.

Jeff

 

you still could have a vacuum leak in the lines that you havent found yet or the plenum gasket is leaking...are you losing any oil or check down your throttle body and see if you see any oil pooling down in there!!!...if you have abad plenum gasket it will cause that too!!!!

 

As I had posted in another post, I see oil at the back of the plenum but it passed the vacuum test noted in the TSB. I didn't know it would cause the vacuum loss at the vents.???

 

I had a similar problem months back. You can take off the dash bezel and pull out the hvac control panel--check the back of the panel to see if any hoses are disconnected or loose. There's a master hose (black) that goes from panel to the vac line 'T' under the hood.

 

Also I believe the transfer case shares the same vacuum lines for engaging the front axle when you put the truck into four wheel drive.

 

I have a 2wd, 5.2L engine. I will pull the bezel to see if something worked loose. BTW, I just got finished tracing all of the vacuum lines from the reserviors at the passenger rear to the front and found no leaks. It might also be the intake.

 

A lot of people have found the curved one under the battery that goes to the cruise vaccuum pod and the group at the rear of the engine on pass. sideare cracked. Pull a vac. test on the line inside the truck/dash area.