I have successfully auto exposed negatives with a >3 minute exposure on my FM3A (as well as F3, FA and FE2) so I don't see a problem with 4minutes. I have also gotten >45 minutes with my Pentax LX and Olympus OM-4T so I have known good references but haven't tried extra long exposures on my Nikons just yet.

To test if your meter is accurate, you need a know good reference - another camera or light meter, steady light and a gray card. If you get 4minutes at f22, then do you should get 2 minutes @ f16, 1 minute @ f11, 30 seconds @f8, 15 seconds @ f5.6, 8 seconds @ f4.0, 4 seconds @ f2.8. This will assure you that your meter is at least responding consistently.

Interesting that some cameras will check exposure at the time of shutter, some will automatically cutoff after a certain time and then some will continuously monitor the scene and change exposure time accordingly.