Ok I've got a 04 Sonata 2.7 v6 that had been parked away for about 17 months, I bring it out of rest and start her up, runs little rough at first but smooths out ( drove about 200 yards) and it begins to run rough sitting in park, doesn't want to go then the worst smell of rotten eggs fills cabin and it does, won't run then.
So catalytic convertors are removed and have clear exhaust car will start run about 5 seconds then dies. The fuel pump also puts out when key turned on then stops, have to turn key off back on to start pump again which runs a few seconds then off again, what am I missing anyone please?

 

The fuel pump is supposed to prime the engine for approx 2 seconds when the key is first turned on. That confirms the computer,fuel pump relay and fuel pump are probably working.. What could be missing is a crank sensor signal to the computer so it knows to keep the fuel pump relay energized and keep supplying fuel.
Crank sensors don't always throw a code and they have been troublesome on Hyundai vehicles.

 

Do you still have the O2 sensors connected?
Do you know how to bypass a fuel pump relay?
Try using starter fluid to keep engine running
If it works then fuel pump is not be energized while engine running
When was the last time the timing belt was changed?

 

Bad fuel could be an issue as well.