575 Brake Issue

Looking for some help on a weird one. The brake pedal on my 575 suddenly got super soft, to the point I won't drive the car. I tried bleeding the master cylinder, then the whole system at each caliper. I first tried vacuum bleeding, but the bleed screws leaked too much air. I ended up just doing a gravity bleed (didn't have anyone to help at the time) until I saw cleaner fluid coming out. Yes, that took a while. That did give me a much firmer pedal with the engine off. It would still go to the floor if you kept pressing, but it was much slower and stayed firm while pushing the pedal. However, start the engine and it all changes. The pedal gets super soft and goes right to the floor with light effort. There's also a "whooshing" sound as the pedal is being pressed (not there when the engine/ignition is off). That sounds like a leak in the power brake booster, but that normally results in a very hard/firm pedal, not a soft one (on other cars, anyway). Isn't the pedal still directly linked to the master cylinder through the booster? Wouldn't a leak in the booster diaphragm just reduce the power assist level?

I looked in the 575 service manual and the schematic of the Bosch ABS system shows A LOT of solenoids and check valves outside of those in the ABS unit itself. Anybody ever hear of one of these sticking open and creating a leak path? The "Theory" section says the system only provides boost, that it leaves the hydraulic system intact for "safety reasons", and so the vehicle can be driven to the dealer. However, it sure looks like there's plenty of ways one of the various recirculation loops could become a leak path. Before I start trying to diagnose a faulty solenoid, etc., under the car I just thought I'd ask to see if anyone has ever had a similar issue with one of their cars. I like to do as much work on the car myself as is possible, mainly for the reason of personal appreciation for the car. It will no doubt save a few bucks, but that's secondary. I like doing the work, and know I'll do the research to do it right (or I won't attempt it). Any input will be appreciated. I realize I'm at a disadvantage by not having an SD-2 or similar compatible high-end scan tool. I do have a Foxwell NT-530 (doesn't do all that much, but shows no ABS codes) and other stuff that doesn't work with Ferraris. I'd prefer not to just throw parts at it either. Not just for the cost, but also because I want to determine what's really up.

Thanks in advance.

 

Thanks. They checked out okay. I did a pressure bleed with a friend pumping the brake pedal and it's better now. Still feels a bit softer than it used to, but the ABS will activate so I' obviously generating enough line pressure to lock the tires. Since I don't have an SD-2, I can't cycle the ABS unit to make sure it's clear of any air.