How can I configure a 74Ls90 to act like a 4017 decade counter. I don't want BCD out want one single pulse per clock, I only need to count to 4.

 

Why don't you look at a datasheet for a 4017?
Then you will see just what is inside of one.

http://www.national.com/ds/CD/CD4017BC.pdf
See page 6.

Consider using some D-type flip-flops with other supporting gates.

 

A 7490 is a BCD counter, it counts 0-9 in binary.

A 4017 has 10 outputs, that count sequentially, 1 pin per number.

They are not very similar.

 

You can use a 74LS42 BCD to decimal decoder or you can add your own decoder built from discrete logic gates.

http://www.national.com/ds/54/54LS42.pdf#page=1