Turbo problem on '88 100TW (rather long) cross posted

[Rennes]

Last few days i have had a following problem: When accelerating hard (pedal to the metal) RPM's go to 4K and then boost's gone. After it drops a bit it picks up the RPM's again and all the same happens all over again. This is what I found out so far: It happens when turbo pressure gets higher then 1,6. I have heard there's some kind of protective circuit that cuts off fuel pump when pressure gets too high? I tried this also. I boosted with my tranny on second gear (tranny is auto) the RPM's went up to 6400 with no problem cause pressure never got over 1,3. So it is the pressure protection issue. More history: When I bought the car few months ago it didn't have any boost at all. Finally I found out that the hose going from the turbo to radiator (with metal rings around it) was broken. So we fixed it temporarely with... it's a long story but the boost came back ok and I could feel the turbo doing it's job. Before the problem with pressure I never got pressure higher then 1,5 at full boost (6000 rpms) I hope that kind of describes my problem. Additional symptoms: It sometimes starts hard. Sometimes it won't start at all. The starter works fine but it seems there's either no fual or no spark. Then after 20 mins or so it starts just fine. New spark plugs last week. Haven't changed fual filter. Any ideas? Mechanics here (Estonia) are mainly just parts replacers I don't trust them. Specially on turbo matters. Thank you in advance