Hi I am irish and was in Canada on a working holiday visa I overstayed by one month what troubles could I have in the future for returning as visitor and what should I do?

My passport was not stamped on exit, and did not receive any departure order

I would like to go back after 4 months as visitor?

There is no way to know until you try to enter. You were not deported because you left voluntarily. Visas and work permits and the like have expiration dates so that the Government knows when/where non-citizens are in Canada. Overstays, obviously, are not looked upon kindly.

There is no way to know what is on the computer until you attempt to enter.

You can also stop at the Canadian Consulate and ask.

I also might want to add... many passports can be read electronically so your departure date might already be in the system... even without the stamp.

And unless there is an open warrant out for you... they are more than happy to let people that overstayed leave. Getting back in might be another story however.