audinatr

Im working on a friends 2002 A4 1.8t tip. It was brought to a local Firestone because the brakes were "extremely hard to press". Well Firestone changed every caliper rotor and pad, along with flushing and bleeding the brakes. For some reason they tore apart the dash as well. Anyways a week or so later it was brought to me.

I looked it over at first and noticed the check valve going into the booster was on backwards and also wasnt working correctly. I changed that and put it the right way. When I started the car I had somewhat normal brakes sitting idle. When I put in it drive and let the car roll the power brakes worked fine. For some reason I had no power brakes in reverse.

I took it down the road, once I got to about 25 mph and hit the brakes I had no power brakes again. I turned back and had a friend hit the brakes while I was under the hood. I can hear the vacuum pump for the brakes turning on and if I pull the check valve off the booster I have vacuum going into the booster.

The other part is the car idles perfectly, but accelerates terribly and has misfire codes for cylinders 1,3 and 4 and random misfire. I dont visibly see anything wrong with the vacuum lines around the booster. Im going to try to get a look at it tomorrow and hook a vacuum guage to it. Does anyone have any suggestions on what else to look for besides vacuum leaks? Or am I overlooking something?

jflow45

Vacuum leak...check the suction jet pump and the rubber grommet that mates the hose out of SJP to the firewall. I had a SJP fail internally and boost back into the brake system which caused similar problems to what you describe.

audinatr

Awesome is there anyway to check how those fail or do I have to borrow a friends vag com and check the vacuum of it?

jflow45

It's a piece of plastic... google suction get pump and check out the images. It can fail by splitting, popping apart or internally. Yours may have failed internally. Remove it and try to move air through it...air should only move in the vacuum direction towards the manifold. It should not boost at all.

If you can blow through the single end while capping off the smaller branch in the "Y" the part has failed and is boosting into your brake reservoir...which can create the problem you are experiencing.

audinatr

Gotcha I was confusing that part with the actual vacuum pump but it ended up being that part haha thanks for the help

jflow45

No prob...mine failed internally after my turbo install. The turbo overboosted to ~25psi, there was a loud pop, I let off the gas and suddenly had no brakes. The SJP failed internally and the hose blew off the vacuum pump.