I have a 1999 Impreza 1.6 wagon.  I am having a problem where the vehicle will run for short periods and then shut down.  If you try to restart immediately it will not restart however if you put it down for a while and try restarting it after some hours it restarts and runs for a short while before shutting down again.  Initially the run period would be for a day or two.  Now its is for very short periods, sometimes less than  an hour. The vehicle is a standard street version with no modifications at all.  I recently replaced a knock sensor.  I have had it on the diagnostic machine but no issues show-up. Has anyone experienced this problem and what are the possible solutions..

I’d be inclined to to look at your fuel pump or pump relay. Turn your ignition on, make sure you can hear the fuel pump priming to start with, it’ll make a slight electronic whirring sound (if that makes sense) from somewhere around your back seat. 

3 minutes ago, WideSam said:

I’d be inclined to to look at your fuel pump or pump relay. Turn your ignition on, make sure you can hear the fuel pump priming to start with, it’ll make a slight electronic whirring sound (if that makes sense) from somewhere around your back seat. 

Thanks Sam but I have checked the fuel system already and that is working fine.

Fuel filter, possibly collapsing

Loud pipes save lives