ECU not priming fuel for few seconds ign on

[ozim535i]

I am new to this forum so here we go....
I own a late 85 unleaded M535i E28. Australian Model
It has part number ecu 0 261 200 059.
The longer my car is parked the longer it takes to start. I had the opportunity to borrow another ecu and noticed the car started very quickly every time. I didn't have the chance to test relays etc while I had the borrowed unit, but the results were obvious. I recently bought a used ecu which runs ok but my car still takes a long time to start I was hoping this ecu would fix the problem.... Both ecu's are not powering the fuel pump relay when the ignition is first turned on to prime the system. They do power the relay when starting and running. I am quite confident I have two ecu's with the same fault (maybe a common problem?). If I had a circuit diagram or knew the common components that cause this fault I coult repair both ecu's.

Can anyone advise?

Update
I have to do some fuel pressure tests. It appears that the pressure when starting should reach (3 bar) within about 0.5 seconds anyway. I tested my cars fuel pressure on the rail not long ago and found the fuel pressure regulator passed all the bentley test while running. Unfortunately, I did not test how long it took the fuel pressure to get up to 3 bar when starting. I suspect I have one of the following problems:
Transfer pump not providing enough pressure (it draws 0.6A when car running) , in tank filter/transfer pump dirty and/or clogged up, Main pump not getting pressure up fast enough.

I any case it would still be nice to know if the 059 type ecu provides a priming signal to the fuel pump relay when ignition is first turned on.

Further update.
Pressure tests confirmed the main pump has poor performance although it can provide 3bar. The check valve in the main pump cannot hold 3 bar. The transfer pump (in-tank pump) had 1/3rd pressure about .12 bar. New pumps, all fuel lines replaced, new injectors, new cold start valve. Not up and running yet because I have to fit the starter after overhaul. Should run well now.