I just bought the house an the previous owners where putting in a bathroom in the basement before they left. They opened the floor to run the pvc pipe to the sewer pipe an just left it open. I started to smell sewer smell every time I went into the basement to do laundry. I capped off the open end but the floor is still dug up. Now I smell it sometimes when it snows or rains hard. The pvc an sewer pipe they dug is below my kitchen an bath on the main floor. Could you tell me what it could be coming from?? Could it be because the floor is still open an the hole is about 1 ft. deep at the end of the open pipe I capped off??

Did they actually start to open the old sewer darinto make their connection? If they were running new pipe in a trench and never made the connection there should be no sewer gas in the home. Any chance of a picture? Could you describe how you capped that pipe?
Thanks,
Bob

Yes it is into the sewer pipe but the other end was left open. I guess they were going to install the toilet an shower from there. I put a 3" plastic cap over the hole at the end of the pvc pipe they ran from the sewer pipe but I still smell gases

Here is a test. If that cap is leaking turn on an exhausr fan somewhere in the house with all exterior doors and windows close. Smell down near the new cap, if its leaking you will get a stronger odor. You could glue that cap with PVC cement but skip the primer since it will come back off someday. You could also grease the inside lip of the cap with Vaseline, something to make an ait tight seal.

An if its not leaking?? What next... this morning I went to do laundry an got a strong ordor... now a few hours later, no smell?

I sthere a toilet in the immediate area? Could be a bad wax ring inder a toilet or even a crack in a vent pipe. Something is allowing sewer gas inside. Are all drains trapped unedr sinks and the like, no other open pipes anywhere?