Passat 96 tdi , only runs for 2-3 seconds

check for codes in the PCM if none the I would check fuel pressure and volume. the volume should be about 1 pint in 15 seconds. the fuel pressure should be 35lbs, continually check pressure until the car dies as sometimes a bad fuel pump won`t show up immediately. also change the fuel filter.

What you are telling me is the engine is firing the plugs but not getting fuel.
When you changed the fuel pump and filter, did you check the fuel pressure at the rail ?
Are the injectors getting power and ground pulse ??

did you change the fuel at the same time as the pump replacement.are you losing fuel pressure/volume that was checked with a gage(have seen it happen with a new pump).does your car have anti-theft on it,it could have set and not allowing the car to start and run.

You need to check fuel pressure at the fuel rail.if pressure is at spec. Check spark at the plugs. Also replace relay for fuel pump if it isn't working. Could be a bad new fuel pump. Pull the codes first.

Exhaust pressure sensor a possibility if it has a DPF (diesel particulate filter). Has it had its fuel pump recall, the oil pressure light could be just the constant cranking and running the battery low.

simplest answer first,and this does not apply to a hot engine,The engine heaters work from a time switch on the door(would you believe)and the routine is, open door,climb in,put on belt,put key in ignition and turn on when orange light goes out.this allows the cold start heaters time to work(about 20 secs).sounds a pain but the number of times this has been all it is,when you put key in ignition, the fuel pump charges the system.hence the squirt noise,also the car has to reccognise the key(immobiliser system)also try using wynns/redexe to clean injectors...

That many miles a replacement new/used engine would be a better route in my opinion.

2003 jetta should have a chain not belt. if there is a large degree of angle from the crank to cam sensors,the ecm or computer will not enable the starter.when you say turn over ,does the starter make a noise and turn the engine,but the car will not start.....?low fuel can burn out an aged fuel pump,because it uses fuel to cool the pump.
have the fuel system pressure tested,or put gas in the throttle body.if it runs for a couple seconds,fuel pump is suspect.
if the engine is dead,you have to mechanically turn it over to see if it is seized.

99 vw passat 1.9tdi was driving sound but just died just turns but wont fire up