So long story short I'm doing some experimenting with different intake manifolds right now. I've currently got the stock 78mm intake on and in the last few days, when I come to start my truck in the morning my brake pedal is hard as a rock until the truck starts. Otherwise the brakes work fine. Does this sound like I have a vacuum leak to you guys or a brake booster gone bad? It never did it until I put the stock intake back on (reusing gaskets of course). The brake pedal is hard just like when you pump the brakes when the engine is off. I'm thinking this stock intake has warped flanges or I smooshed a gasket

 

I thought that there was some sort of check valve that maintained pressure in the booster, whether it be inline or internal to the booster. Doesn't make sense that a vacuum leak at the intake would cause that, since as soon as you turn the engine off, it bleeds off vacuum anyway. Wierd how it happened after swapping intakes though...if you do in fact have a vacuum leak you'll be able to see it with your scanning software, your A/F ratio will be lean. You can always check with the engine running and spraying some carb cleaner also...

 

Meh, it never did this with the 90mm intake installed. It did this only with the stock intake installed. I guess I should have rephrased my question earlier, I assumed there was a check valve somewhere in the braking system as well. Tomorrow I'm going to test my theory. I'm going to shut the truck off, yank the brake booster hose from the intake and see if the pedal is hard after doing so. If so, I may have a vacuum leak with the stock intake. My fuel trims seem to be in line BUT I notice with the stock intake manifold, during initial startup in the morning (cold) the truck will run lean on the pass side cyl bank like it did last year. When I put the 90mm intake on, that all went away. I guess it's time to put the 90mm back on. I'm still waiting for some parts before doing so

 

Do you have a wideband? Have you thought about getting new gaskets? GM recommends changing the TB and intake gaskets I believe every time they are removed. I think I may have a leak from either of those...

 

No wideband here. I also don't need to touch the TB gasket as the TB has never been off either intake manifold. The intake gaskets also have been reused about 4 times without problems. The problem keeps rearing its head with the stock intake though. I'm pretty sure the flanges are warped but I don't have a good straight edge to test the intake with. The problem with the pass side cyl bank running lean goes away after about 2 minutes of driving. Also, it's so minute that brake cleaner or water will not change the running characteristics of the motor.

 

That's interesting, sounds like you narrowed it down to something with the stock intake/gaskets. I have noticed in that past that when you pull the brake booster hose off of the intake or booster of a car or truck, that you get a quick "puff" as vacuum escapes, maybe there's something to your theory...

 

This morning I got in the truck and the brake pedal wasn't rock hard like it's been in the last week. It must be self healing or something I'm actually thinking it's either intake gaskets OR a combination of bad intake gaskets AND a faulty brake booster check valve. Autozone has them for only $10. I'm going to grab one on the way home and swap it for the hell of it.

 

Keep me updated on the gaskets.

 

Uhhm, so I popped the hood today at lunch and apparently there's no check valve on the new trucks. The vacuum hose runs into this electric powered vacuum motor incase you lose engine power. So either this device goes bad (WTF is it technically called?) or I have a vacuum loss in the hose somewhere. There SHOULD be a check valve inline somewhere though. Maybe it's in the electric powered pop can

 

Ok, so I stole this picture from Ebay. If indeed my electric vacuum pump motor is bad, it looks like a guy could remove it entirely and just run the vacuum line directly to a brake booster check valve (if the sizes are the same). It just is there to provide stopping power if the engine dies.