Hello,

I have a 1999 EK3 saloon with the d15z6 engine in. I have replaced the disc and pads both front and rear, installed a brand new master cylinder, fitted new copper brake lines underneath, fitted a new brake booster and bled the brakes several times with the help of my partner.
when i bought the car the brakes wouldn't work at all and the pedal would just sink to the floor. when the engine is off it now build up pressure on the brake pedal however as soon as the engine starts, the pedal cant hold any pressure. I have checked for leaks and there is no leaks anywhere, i have also followed the instructions in the haynes manual to test the booster and this passed. I am really struggling to understand what the problem is. when the engine is running and i press the brake, the revs shoot up by 500 rpm too. I am starting to think that this could be a vacuum issue however i don't know where to start with this. other forums i have read state that it is a bad master cylinder however this was brand new and the booster passed the tests? I have bled them several times too and there isn't any air coming out. any ideas? thanks

also when i press the brake pedal down with the engine off, there is a squeek sound that comes from the engine bay, kind of sound like a chicken/air in the system but i cant seem to locate it. cant hear when the engine is on due to the noise from the engine.

 

There are a couple of things you might try in order to locate a vacuum leak, which is what this sounds like.

Method1: Set Yourself On Fire. If you use this method first have a helper with a fire extinguisher standing by. Using brake parts cleaner or carburetor cleaner and with the engine running carefully spray it around the engine. When you hear a drop or sudden rise in RPM you have located the leak. As the name suggests, you may set the engine - or yourself - on fire as what you are spraying is highly flammable.

Method 2: Scare Yourself To Death: Less likely to start a fire but you may hear a loud bang if it ignites. Also have a helper with a fire extinguisher standing by. Using a propane torch, open the valve but don't light it. Direct the propane around things on the engine. Again, if the RPMs change you have found the leak. This is safer than method 1 because you won't have a lot of flammable liquid running all over the place. The propane might ignite, causing a loud bang but probably won't start a fire. If this happens be sure to check your underwear afterwards and change as needed.

Method 3: Hose The Damn Thing Down: Do this only on a cold engine! Using a water spray bottle spray water around the engine. If the RPM changes you MAY have found the leak; or, you may have just killed the engine because water and internal combustion engines don't really mix well. If this happens, dry everything off, restart the engine (if you can) and repeat several times to confirm that you have found the leak.

Good luck! I've used all three methods and while I've been lucky and never set myself on fire I've never found a vacuum leak using them either. I found a leak in a 2006 Dodge after trying all three methods with no success by pure chance - I just happened to change the right part.