B204GT oil pump not priming

So I have an issue with oil pressure build up after the engine rebuild (16v 2.0 turbo). Engine filled with oil, spark plugs removed, oil pressure gauge in the oil pressure sensor hole & trying to get some oil pressure reading while cranking.

Several cranking attempts done, zero reading. Then I have checked the oil filter and it's empty. I am sure I installed the oil sump oring correctly and also the oil pump seal. So I guess the issue is just the dry oil pump?

How should I proceed? On the picture below it seems I could inject some oil through the relief valve(2)? Should I fill the oil filter? And how much if so (I have been reading that all the way up can also cause issues?).

Can you disconnect the timing belt and put an impact driver on the shaft that drives the oil pump and spin if for a bit? That is how I primed mine out of the car.

After I put in the car I removed the spark plugs and disconnected the feed line to the turbo to validate it was circulating oil. It took a while as it had to fill the engine, oil cooler and remote filter.

Well, I don't have an impact gun here...but indeed I've just ordered the flexible 1/2 ratchet wrench extension, using the 3/8 and 1/4 adapters I should be able to run it with a drill. It's limited space with everything already installed
Any hints regarding pre-filling the oil filter?

I had my B234F oil relief stick open due to contamination from too much pink goop used in the area.

I remember that the B204 did not prime when we tried it with the starter.

After probably a minute of cranking (no spark plugs fitted so easy on the starter) we just started it and oil pressure was present in a few seconds, just like after a normal oil change.

Battery drill should have enough speed to rev the pump fast enough to get it to pump too, of course safer with your fresh engine!

Yep, after filling the oil filter with oil and spinning the oil pump gear separately by drilling machine the pressure finally became present and now it is happily primed.

One related question: is it normal that the oil pressure drops like this after I stopped cranking?

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Seems normal to me. No pumpage, no pressure. As far as i know there is no 1way hydraulic valve on the output side of the pump that would prevent pressure to drop.

Yep, normal.
Nothing gets lubricated unless the oil *flows*.
In one side, out the other.
Parts can, will, and are designed to "leak" the oil at a controlled rate.
Through crank bearings to flush out any bits of "wear", and let clean oil in.
Out cam bearings to keep the lifter bores full.
Out the "squirters" to lube/cool the cylinder walls.
Through the turbo bearings to let cool oil in, and prevent instant seizing.
etc, etc, etc........

It is NOT good to lubricate the shop floor, the drive pulleys, the clutch disc, or any other "outside the engine" bits, so keep an eye on those.

Thanks guys