It won't be the crank sensor as it would not fuel at all if this was not signalling.
Try pulling the plug leads off one at a time to identify the affected cylinder if you think it's running on 3, then you swap the lead with another and see if the problem moves to the cylinder with the suspect lead, if it doesn't the leads are ok.
This leaves fuelling as most likely, or a duff plug, again can do swappsies with the plugs.
tabetha