Outside Air Blows Into Cabin

[jaythebaron]

Hi,
I have a 94 wrangler 4.0 and am having a problem with the outside air coming through my cabin vents when I accelerate. This is not very fun especially for this time of year! Could this be a vacuum problem somewhere? Thanks in advance.

 

[Saddle Tramp]

I have had the same problem before. The fresh air vent door is not closing or is cracked/broken or something to that sort. Are you getting water in under the dash too? If so the air box under the grill at the cowling may be the problem too as they will crack or the drain hose out of the side becomes plugged.

 

[jfrabat]

What's happening is that at WOT, the vacuum generated by the engine is not enough to activate the vacuum servo. I solved this in mine by installing a vacuum reservoir in the vacuum line right before it goes through the firewall. The reservoir was about $15 and IIRC I bought it at Summit Racing... It's one of those used for Cruise Controls, so you can also get one cheaper from the junkyard.