hmmv injector pump swap need help

i bought a hmmv injector pump and i am in the process of swapping old for new in my 1009. when i took the old pump out there was a golf tee looking plunger in the center of the rotor. it was not on the hmmv pump so i decided to swap out the old one. when i pulled it out of the old one it had tension like there was a spring behind it holding it in place. when i put it in the new pump there was no tension at all going in or out. what is supposed to hold this thing in place? in the pic below you can see the small circle in the center of the rotor and that is the piece i m referring to. i know the pic is not a db2 pump but it looks similar.

Thier is a spring behind the plunger, some slide out easy some have to be pulled out. pumps will interchange but you have to change the top covers. Te CUCV is 12 volt and THE HMMV is 24 volt . If you need any help give me a shout, anit far from you

ok cool thanks i was not sure if there was a spring or o ring creating pressure. i am aware about the top plate the only problem i have run into is the hmmv top plate screws are a special 5 point torx security screw and i have not been able to find a bit to fit it anywhere locally. i was trying to avoid ordering a whole set of bits for 3 small screws.

If you don't mind messing up your HMMV screws, just slot them across the middle with a die grinder and take them out with a flat tip screw driver, or bring it by the house and I'll take them out.