Brakes-ebcm,dumpvalve or combination?

[chrisz]

I own a 1992 Chevy K1500 350 TBI Z71. My problem is with my brakeing system and was wondering if anyone could help. I noticed that the brake pedal was traveling further than it should and also the brake warning lamp illuminated when i pressed the pedal to the floor and stayed on. The problem got worse to where the pedal went right to the floor but i noticed that with the engine off it would be firm. I have no leaking wheel cylinders, new pads and shoes and so i replaced the master cylinder, bench bled it, bled the system to no avail. I then ran a diagnostic self check on the truck and it came out as a code 3=open dump soilenoid or EBCM malfunction. I went to a junkyard replaced the Dump valve and it still did not work. Went back to junkyard and got an EBCM, nope still not working. What could it be? I thought it may be the master cylinder as i have had remanufactured parts that are bad before so i removed the two lines from the master cylinder and capped them with threaded plastic caps and the pedal was hard suggesting a good master cylinder. The only thing i have not replaced is the combination valve. I dont know if the junkyard parts are bad or not(maybe the reason why the truck was wrecked cos he couldnt stop)but any help would be greatly appreiciated!!

[maddoggy71]

Sounds to me like you're sucking air somewhere in the brake system.

First, I would bleed all 4 brakes and look for obvious leaks or loose connections. Typically the problem will be fixed momentarily... but you may get lucky and fix the problem for good.

If the brakes work great for awhile and again your pedal starts moving towards the floor, you definately are sucking air in the brake system.

Typically the calipers/master cylinders need replaced somewhere. I had the exact same problem/symptoms you are having... I replaced all cylinders and master cylinder and hoses. Turned out I had loose fitting where the front brake lines split.

Good luck...