Ok, we have a couple of units that this valve just won't open as a result of exhaust back pressure but will stay closed until coolant reaches about 180 degrees. When this happens the vehicle won't go over 30 mph or so and the black smoke is so thick you can hardly see the back of the unit. The back pressure signal seems to be getting to the computer but it doesn't open the valve. We want to either fix them or disable them, any suggestions??????? I have tried unhooking the wire connector at the turbo pedestal but the valve still closes
Oh, I forgot to mention that these 7.3 Powerstrokes are T444Es in 1997 & 1998 International school buses

 

They must work differently in a school bus cuz disconnecting the wire harness usually does the job. I guess you could pull the turbo pedestal and cut the valve out of it but, You might want to fix them just because they are in a school bus or it'll take a long time to get heat especially if you are in the snow belt. Don't want to freeze the kids

 

I know what you mean about a slower warm up but we may have to choose between the kids shivering a bit longer or having them choking on particulate emissions....

 

The servo may be stuck in the closed position, a good way to check is keep eyes on the turbo when you start the Vehicle, you should see the servo extend to close the EBPV. If it is extended before you start it the servo may be bad, or may have lost power in the extended/ closed position. I do not know if you can move the servo manually. there is a spring mechanism that is designed to cause the EBPV to work more effectively at higher rpms, and work less at lower rpm to avoid pnuematic lock or stall from excess back pressure. This spring will make the vehicle seem normal at idle when in reality the servo is remaining in the closed position. You may be able to jerry rig the valve open with wire to trouble shoot but it is not a good plan for a long term fix.