Won't start after refitting fuel pump

[TwoStrokeSmoke]

My 1995 2.5 Di had a very strange fault. It started with cold start difficulties 1,5 month ago (5-8 seconds of holding on the key needed to start) and after 300 kms or so, it lost power due to excessive AIR pressure in the Bosch fuel pump. After taking the fuel feed line off (always made a popping sound due to the air pressure) and sitting for a while, it started again and worked for the next 30-50 kms. Its last ride was 10 kms to the 'workshop' where it stopped running, no idle at all.
Due to the symptoms, air leakage and/or vane pump fault was suspected, so I took the pump apart and fitted new rubber gaskets, rings, another pressure valve, another vane pump (the original looked good though) and cleaned everything. The return line valve was clogged, after cleaning that there is no air pressure buildup in the pump anymore. Refitted the pump, belt, etc. and still didn't start at all.
Since then I checked fuel lines, filter, timing, shutoff solenoid (took off the valve from inside to sort it out), injectors were tested by a regular pop tester, bled out air from the pump, etc etc and still doesn't start at all. With brake cleaner sprayed into the intake manifold it burns the cleaner and pushes out extreme amount of white / greyish smoke from the exhaust pipe. Timing is set correctly, if I loosen the high pressure fuel nut the fuel is sprayed out so the cylinders get fuel. Still doesn't work. Leakoff mod not done yet, 1 or 2 out of the 4 leakoff caps have broken rubber rings (they aren't available here anywhere) but it was working for more than a year woth those rubbers and original leakoff arrangement...
I ran out of ideas, can anyone please share me some experiences like this with solutions? I really need the van coz I have lots of jobs that can be done now only by that...