evening all, seem to have loost some boost, have 96 uk turbo and dump valve seems to be stuck open, not sure on make but has a series of holes around it and allen bolts round the top, is it possible to open it up and clean it out? can hear a hissing noise coming from engine area when driving and when car is idling i can see into the holes, surely they should be closed and only open up when i let off throttle? only had car a few days and was boosting fine and dumping but suddenly stopped, can heat the turbo spool up but cant feel it kick in and doesnt dump anymore

 

check all the pipework on the turbo, some piping may have coroded and gone crap somewhere.

try cleaning your boost solenoid (this seems to solve everything from a flat tyre to the death of a close pet)!

there is a little nut at the top of the dump valve that has a pipe that leads to the engine, check the nut is done up tight and that the pipe has no holes - this sucks the spring up on tickover/no boost and needs to be solid. the dump valve only closes up when the turbo is on boost.
check and tighten up the pipework that runs from the bottom of the unit to the turbo pipe - if its not closing up on boost then the turbo is either not sucking it closed when on boost or you need to get in and lube up the dump valve or just get a new one. also check the tube that has been capped off (runs from the air box to the engine right by the dump valve) - this could be letting in air.

its more than likely just a crap bit of plumbing