Relays not closing

Hi all, im getting a bit of a headache with a project im working on.

My adruino pins are outputing 4.9~V but when I connect them to a 5v relay it drops to 2.3v

The relays im using at these:
http://docs-europe.electrocomponents.com/webdocs/1264/0900766b812649be.pdf

When i wire the relay directly to 3.3v or 5v pins it closes just not on PWI pins.

Any ideas?

You cannot power a relay coil directly from an I/O pin. You must use a transistor. What is happening is you are drawing too much current from the pin and the voltage is sagging.

The link you provided is for a 12 and 24 v relay.