ok,, just started last night.. i start the truck.. let it idle for a min.. like always.. i kick on the A/C and i start driving,, i go down my road towards the main road, stop and a stop sighn and make a right hand turn,,, i usually get all up on the throttle b/c its a blind interesection,.,, and i notice if i have my fan speed on 4 - full blast- it will suddenlly stop coming out of the dash vents... i can hear it still blowing at full speed but it just stops... almost like a door got shut,,, when i let off the throttle it starts back up again blowing through the vents... i had a P0442 pop... a evap emission control system small leak detected...

it does it all day.. it doesnt matter if the truck warms up or how long im driving for... if i get on the throttle it stops blowing and then if a let off for a second itll start back up again

any ideas?

 

Mine doest the same thing. When I get on it, the air moves from the vents to coming out of the defroster vents up top. It has something to do with the vacuum system that controls the swap over from front vents to top vents. I think there are actually a couple of threads on here about it. I seem to remember something about a part that would fix it, almost like a backflow preventer. BTW, I still can't get over that burnout!!!!

 

Standard answer ... vacuum leak ... but your's is going to be easier to find (I believe). Your's is limited to the Evap system. Loose gas cap? Hose to the canister? It's really a pretty small system.

 

Yeah i had the same problem with mine(although it was a p0455), I found out the evap leak had nothing to do with the other vacuum leak. My leak was the lines running from the transfer case to the CAD the vaccum lines down there are firm and can get very brittle as i found out. easy fix and thanks to help on this forum that annoying AC switching vents is gone!

Good luck! i found mine by visually inspecting (laying under the truck)

 

I agree. Vacuum leak. Check the lines and check the check valve. Check?..lol


I know I have a diesel but when I installed my hydroboost, there was no vacuum booster anymore. Now all my vacuum pump does is the A/C , the servo on the front axle, and the cruise controll. My heat/ac blows harder than ever because the vacuum sevos are getting about 22 inches of vaccum. When the doors close to reroute the air, they slam shut now.....lol.


Anyway,

Good luck.

 

i actually found one of my hardline vacume lines worn from the tcase to the cad the other day... and theres a open gap in one.. 4X4 still shifts fine that thats prolly where im getting my code from...

thanks for the tips guys.. maybe ill start fiddling with the evap and the vacumes behind the dash

 

I agree with Deisel check the check valve. Under heavy accel with the vacuum leak you found you'll have a drop in vacuum pressure. The check valve should help prevent that from affecting the vents directional system but if the if the check valve isn't working then you'll loose and gain vacuum on that system as well depending how much you have your foot into the accelerator.