A Line Mechanic reports finding fuel dripping out of the left wing center tank fuel pump panel during a Maintenance check that included an override jettison pump diffuser check on a B767-300. Further investigation revealed the fuel pump installed was not the correct pump for the aircraft.

Narrative

One of our B767-300 aircraft was in the hangar for a Maintenance check. Mechanic 'X' and myself were assigned to perform the left-hand (LH) side override jettison pump diffuser check and other exterior job cards. During the walk around I found fuel dripping out of the left hand wing; center tank fuel pump panel. After removing the panel; we found fuel dripping out of the inboard side fuel pump on the center; left hand fuel tank. After further investigation we discovered that the fuel pump installed was not the correct fuel pump for our B767-300 nose number. The incorrect fuel pump had a -37 number and a part number effective for other B767 nose numbers. This is verified on Illustrated Parts Catalog (IPC) Chapter 28-22-05-001A; page 'X.' The correct fuel pump is noted in IPC 28-22-05-001A; page 'Y;' which is effective for this aircraft's nose number.This illegal fuel pump was removed on my shift. At this time we were unsure if the correct sleeve was installed with the -37 pump or if any sleeve was changed by the Mechanic. Dayshift mechanics continued working problem. I made a Write-up against the aircraft.