hi guys i have recently removed a bleed valve from my uk 2000 and now the boost is sort of bouncing when it comes in it hits full boost but i wont hold it drops off and comes in again and so on so on any ideas guys as this is gettin me annoyed??

 

Going to be difficult to help you on the basis of the information you've given us so far chap, need a lot more than this, starting with the model year of your car.

Other than that, can you describe exactly what you mean by the boost "dropping off and coming in again"? Does the boost disappear gradually, or suddenly, like it just drove into a brick wall?

Also, if you have a boost gauge, what sort of reading are you seeing at the point it cuts out?

And finally, if you've removed a bleed valve, are you certain you've reconfigured the boost control pipework correctly? If it's a car with a two port solenoid, are you sure you've used the correct bore restrictor, for example, and if so, are you sure it's in the right place (i.e. between the compressor outlet and the t-piece)?

 

hi its a 99 uk turbo. the boost builds up to about 16 psi then it slowly drops back to about 12 psi then it will builld back to 16 again it will keep doin this in one gear

 

If you have a standard (i.e. non-PPP, non Ecutek) car, sounds like it's suffering overboost and consequent oscillation.

"Full boost" on a standard UK MY99 car is around 13.4psi, so if your boost gauge readings are accurate, it's overshooting the target by something like 20%, which will cause the ECU to pull a lot of pressure control solenoid duty to try and bring it under control. It then drops below target, ECU compensates by putting the solenoid duty up again, and the whole process repeats.

There are a few potential explanations for this behaviour. Oiled up boost control pipework is one, a full decat can under certain circumstances knock things out of whack too.

However, given what you've said about removing a bleed valve to refit the standard pipework, are you sure you've refitted everything correctly (and did you re-use the fittings that were originally on the car)?

It sounds like the restrictor you're using is too small. It should be 1.2mm on your model of car so check this is the case, and if not, get a set of mini drills (or reamers) and open it out a touch.