Alpine951

Been trying to hunt down a possible large vacuum leak. I finally bought a mightyvac. I disconnected the booster vacuum line at the point of the T where that blue check valve is behind the intake manifold. I attached the mightyvac to the end of the hose and no matter how much I pumped I could only get 8 inches. Not knowing what the check valve that sticks into the booster is supposed to do , I yanked it out. When I yanked it out a big rush of air came out of the hole the valve was in. With the check valve removed I can suck on the end of the check valve that the vacuum line attaches to but can not blow air into it. Is that how it is supposed to work?

I then put the valve back into the booster and attached the mightyvac to the end of the check valve and get 8 inches but it takes a lot of pumping.. What does this mean?

Alpine951

Anybody?

Droops83

It sounds to me like your brake booster and check valve are working exactly as they are supposed to. The fact that you got a big rush of air from the booster when you pulled the check valve out means that it is most likely holding vacuum and not leaking.

The one-way check valve is designed to allow vacuum to enter the forward/working chamber of the brake booster, while not allowing it to escape in the other direction past the valve. This ensures that even if the engine stalls and the vacuum supply ceases, there will be a few vacuum-assisted brake applications remaining. You were not able to blow air into the check valve in the direction of the intake manifold, so the valve is also likely to be OK.

It was a good and quick/easy component to check, however. If you are still in doubt, you can disconnect the booster line and cap it off; if the engine still runs the same, the problem likely does not have to do with the brake booster circuit . . . .

What makes you think that you have a vacuum leak? Do you have a wideband A/F gauge? Vacuum leaks generally cause very lean running at idle and low RPM, but the A/F ratio generally improves with RPM/load.

Chris

Alpine951

Thanks Chris. That is what I thought unfortunately. Over the past 12 months I have been trying to track down what appears to be a large vacuum leak . You will find a bunch of threads by me on here over that period of time regarding this. Wideband AFR at idle is 17-18+. Done a bunch of pressure testing , smoke test, thrown money at new parts but still can't find it yet. when it happened afr was OK while cruising at 14.7 dithering but has gotten progressively leaner now. The hunt continues.

gruhsy

Have you looked inside the car at the heating/ac system? Off the top of my head I cant remember the configuration under the dash or if it would affect anything. When I build up my car I pulled apart the heating system and there are some Vac lines in there.

Alpine951

I did look at those lines inside the passenger footwell and they were all connected. I don't recall if I had sprayed them though when I did any of the pressure tests. I may test again this weekend and if I do I will spray then with some soapy water. Those lines get vacum from the vacuum canister next to the battery.