There should be vacuum behind the MC, but the "poof" sound seemslike air pressure bypassing the rear MC seal. Is your power assist working okay? Is this sound happening only when the engine is off, or when it's running as well? If it's only when the engine if off, then I wouldn't worry about it since there is no engine vacuum sucking the air out of the booster and pressure can be present when the pedal is applied.

 

I pulled the two wire pigtail at the front proportioning valve(the one with the button)- both brake lights stayed on with the key on. The only way I can get the lights to go off is to pull the 10amp fuse on the side of the dashboard. There is a 40 amp square fuse in the fuseblock under the hood marked braking system. I pulled that but the lights stayed on. [>:]

 

Well that explains it, the proportioning valve is not what has the light turned on. Something else, probably anABS issueis whats causing the light to be on.

 

The thing the usually goes wrong with these RWAL systems is the speed sensor mounted in the top of the differential. If you pull the connector and connect an ohmmeter to the sensor, it should read less than 2400 ohms. Anything higher and the sensor is no good.

 

Alloro, I tested the sensor on the diff. 1669 ohms, so it doesn't look like that is the problem. Now where should I look?

 

Now you're stuck going to the dealer and having them plug their DRB-III scanner into it.

 

Darn. Not what I was hoping to hear. My friend that I got this van from took it to the dealer and they said that it was the pressure limit switch (proportioning valve). We have been focused on the front proportioning valve (with the two wire pigtail). Do you think the problem is in the proportioning valve looking thing that is behind that front one. It has a flat connector with either 3 or 4 wires, and looks like it goes to the rear brakes (which is where the abs is). Am I correct in thinking this? Thanks.

 

That's the ABS solenoid assembly and the ABS computer is right behind it. The 4-wire connector comes from the ABS computer to control the solenoid valves. But I though you replaced that at the same time as the proportioning valve?

 

Yes I did replace that solenoid with a junkyard unit. Now I'm thinking of going back to the yard, and grabbing another solenoid and computer. What do you think?

 

anything else I should grab while i'm there?