Hi, I have a 96 blazer and when I brake, the brake pedal slowly looses pressure and then the engine starts to run rough. I am assuming a vacuum leak since the braking is causing engine issues, I have visually check the hoses but I am not able to find a leak anywhere, I haven't put a vacuum gauge on it to verify. There doesn't seem to be an issue when I am driving along and I brake it is just when I get to a stop and the engine is idling low. Any other ideas or recommendations on how to find a vacuum leak if that's what it is. Thanks.

 

You could have a leaky brake vacuum booster that is using more vacuum when applied than it should.

Shut the engine off and remove the check valve from the front of the booster. You should hear a rush of air entering the booster. If you do not, then the booster is leaking. If you do hear it, the next step would be to have someone apply a little bit of brake pressure. Listen for a leak in the booster.

 

Thanks for the fast reply swartlkk, I pulled the check valve and I could hear the air get sucked in. I then hooked it back up and started it up and had my wife push on the brake, I can't hear a leak anywhere around the booster, it sounds like it could be where the vacuum hose goes into the engine from the booster. I pulled that out and the seal seems to be fine so I'm not sure if I should try replacing it to see if it helps or if I am hearing something else. Any other suggestions?? Thanks.

 

I diagnosed this one on the '89 Bronco II I'm selling to pay for the '95 Blazer I'm about to buy by having someone apply the brake in park, letting the engine get rough, then kinking the vacuum hose upstream of the check valve and seeing if the idle smooths out. In my case, it turned out to be the check valve itself: the problem went away when kinking the hose between the check valve and the manifold, and not when kinking the hose between the check valve and booster.

 

I pinched the hose between the brake booster and the intake and the engine started to run fine. So, since the check valve held the pressure I assume that it is fine, so I will be replacing the brake booster this weekend and hope that solves the problem.

 

Replaced the brake booster and I have normal brakes again

 

Good deal! Thanks for the follow up!

 

Mr. T - I have the same exact issue with my '96 Blazer. Was it difficult swapping out the booster? I have the new booster, and I'm ready to get this thing fixed. I've heard that it's difficult to remove the upper right bolt that secures the booster. What type of tools did you use?

 

Yeah it took me about 2 hours to swap the booster in my truck, however I went to the junk yard and pulled a used one out of a truck in about 30 mins, strange how much quicker things go when you don't care about the vehicle

You'll want a long extension for your socket wrench, I couldn't find my long extensions so I just connected a few 3" extensions together, I also used an elbow right after the socket iirc. The top right bolt is the hardest, I took the bottom of the dash apart and that helped get a better angle on it, I think I went from above the steering shaft. Good luck.

 

Thanks! I'm going to swap it out tonight. A cold 12 pack will hopefully help.