after running for 20-30 minutes the engine will stall, i checked the fuse panel on the interior of the vehicle and noticed a 15A fuse blown labeled simply as "ENGINE DEVICE". after replacing this fuse it starts right up only to stall and blow the same fuse again 20 mins later. it will not start without this fuse in. if i knew what this fuse controlled then i could troubleshoot the problem better... any ideas?

He has a 97 Rodeo.

yes, its a 97 Isuzu Rodeo... the fuse position is CB-3.

could be the voltage regulator on your alternator maybe.