1990 Volvo 240 oil blowing out filler cap

OK you first need to check the PCV valve system make sure it is clear. Then I would check the compression. Get back to me and we will go from there.

where do i find the fire screen and oil trap to check it

There is no oil trap or fire screen on a car. I did check just to make sure and there is no listing for either of them. The turbo model has an oil trap to return oil back to the pan but that is connected to the oil pump.
Now If oil is coming out of the valve cover that is either because of the pcv system being pluged or bad rings that are allowing to much pressure in the engine and it has to go somewhere. So I would check the PCV system and do a compression test and it should be 128 psi per cylinder. Get back to me with what you find.

I went to volvo this morning and bought a fire screen for my car and it fixed the problem.Thanks anyway.

P.S. it also has a oil trap.

They are not showing it in any repair manual so Volvo is not sharing this info with the aftermarket. If you feel up to send me a pic as I would like to see that. It maybe that the aftermarket calls it something else. As for the oil trap it only shows that on a turbo and say's it is connected to the oil pump I couldn't find any more info on that. Thanks anyway.

Volvo calls it a flame shield,its the size of a quarter and goes between the intake plenum and the oil trap.Its only a 8.00 part

Well I will have to look at a breakdown and see what it shows me. I am alway's into learning more. Thanks.