On May 28, 1994, at 1733 central daylight time (cdt), a Cessna P-210, N4UD, registered to D.C. Leasing of Zion, Illinois, and piloted by an instrument rated private pilot, was substantially damaged when it was ditched into Lake Michigan, approximately one mile northeast of Milwaukee, Wisconsin. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 flight had been operating on an IFR flight plan. The pilot and three passengers reported no injuries. The flight departed Mackinac Island, Michigan, at 1600 eastern daylight time. N4UD's pilot said he obtained a weather briefing for his flight to Mackinac Island early in the morning of May 28, 1994. He said his flight planning information sank with the airplane and was lost. According to the pilot, both fuel tanks were topped off prior to his departure from Kenosha, Wisconsin. He said he looked at the fuel two times before departing. The pilot was asked if he used a dip stick in the fuel tanks. He said that he did not. He stated he looked at the fuel gauges to check the quantity. According to the Federal Aviation Administration's (FAA) Milwaukee Mitchell air traffic control tower (ATCT) transcripts, the pilot did not advise the controller of a low fuel situation or declare an emergency. The controller asked the pilot if he was experiencing difficulties several times and was told "No we're not sir" by the pilot. After performing a 360 degree descending turn the pilot asked for a second 360 degree turn. The controller assigned the pilot a heading of 360 degrees due to inbound traffic. Approximately three minutes after being assigned the 360 degree heading the pilot told the controller "OK I got an engine failure sir I'm coming in." The controller asked the pilot for the number of people on board and how much fuel he responded: "Yea looks like we're empty sir." The airplane landed in Lake Michigan, about five miles northeast of Mitchell Field. All four occupants were picked up by nearby boats before the airplane sank. The Coast Guard reported that no fuel slick was observed at the accident scene. During a telephone interview with the pilot it was revealed he noticed his airplane's fuel tank gauges "...dipping..." faster than normal when his airplane was adjacent to Sheboygan, Wisconsin. He defined dipping as the fuel gauge needle moving between the empty and the one quarter full mark. The pilot was asked what his fuel gauges were showing when he was adjacent to Sheboygan, Wisconsin. He said he couldn't recall but knew they were "...below minimum." The airplane was removed from Lake Michigan on May 29, 1994. Eight days after its recovery the airplane was inspected by an FAA Principal Maintenance Inspector (PMI), and a safety investigator from Cessna Aircraft Company. The fuel tanks were empty and portions of the wing's top skin were collapsed inward. The airplane's engine developed 2,700 RPM during its test run. No contamination or dirt was found in the fuel cells and the finger inlet screens. No fuel stains were observed at the fuel cap areas or at the wing tip vents. The fuel cap seals and filler ports were not damaged or worn. N4UD's engine was equipped with a Turbo-Plus after-market intercooler which was installed on July 24, 1991 in accordance with STC SA2390NM. The FAA approved flight manual Supplement dated May 11, 1984, which is required for operation with this modification, was not found with the airplane documents. The STC's information states: "... intercooled charge air, being more dense, results in more fuel burned... ." The airplane's fuel pump, metering valve, and fuel pressure gauge were examined at B & S Aircraft Parts and Accessories, Incorporated, Wichita, Kansas. The fuel pump was tested and found to function normally and within limits set by the manufacturer. The metering valve test indicated the unit operated correctly. The fuel pressure gauge was tested and was not operating properly. The gauge should show pressure from 3.0 psi to 19.5 psi. The needle did not move until approximately 20 psi of pressure was applied. The gauge pegged out and stuck when 26 psi had been applied.