Narrative:

On aug/xa/07; my student and I were on an instructional flight originating in dab with a destination of cdk. The flight to cdk was uneventful. At cdk we shut the aircraft down for approximately 1 hour. Upon return to the aircraft and before departure; I performed a preflight inspection. I noted no visible defects with the aircraft. We started and taxied to the runway for our run-up. Run-up was normal and no engine abnormalities were observed. Takeoff and initial climb out were normal. When turning crosswind; we heard a loud 'pop' and the engine began to run rough with moderate vibration. I looked at the engine gauges and noted: oil pressure; and oil temperature were both stable at appropriate numbers. Egt gauge showed a maximum full scale deflection; and fuel flow was fluctuating between 10 gph and 15 gph. I was the PF at the time; so I kept control of the aircraft. Since we were in the traffic pattern I elected to return for a landing. While flying the downwind I adjusted the power to 1500 RPM. The vibrations decreased and the engine ran smoother. I executed a cautionary landing with power; the rest of approach and landing were uneventful. We taxied and shut the aircraft down. Upon inspection of the aircraft I noted that the forward left cylinder (when referencing the pilot's seat) had a broken fuel injector line. The line had separated about an inch above where the line connected to the cylinder. I also noted that fuel was dripping out of the line onto the engine. During the event I elected to keep the engine running. I noticed that the oil temperature and pressure were at normal levels; and when I decreased the RPM the egt came to a normal level. Had I observed unsafe levels in all 3 gauges I would have shut and secured the engine while setting up for a landing at cdk.

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Original NASA ASRS Text

Title: C-172 EXPERIENCED ROUGH RUNNING ENG WITH ASSOCIATED VIBRATION DURING CLIMBOUT. PLT RETURNED FOR PRECAUTIONARY LNDG.

Narrative: ON AUG/XA/07; MY STUDENT AND I WERE ON AN INSTRUCTIONAL FLT ORIGINATING IN DAB WITH A DEST OF CDK. THE FLT TO CDK WAS UNEVENTFUL. AT CDK WE SHUT THE ACFT DOWN FOR APPROX 1 HR. UPON RETURN TO THE ACFT AND BEFORE DEP; I PERFORMED A PREFLT INSPECTION. I NOTED NO VISIBLE DEFECTS WITH THE ACFT. WE STARTED AND TAXIED TO THE RWY FOR OUR RUN-UP. RUN-UP WAS NORMAL AND NO ENG ABNORMALITIES WERE OBSERVED. TKOF AND INITIAL CLBOUT WERE NORMAL. WHEN TURNING XWIND; WE HEARD A LOUD 'POP' AND THE ENG BEGAN TO RUN ROUGH WITH MODERATE VIBRATION. I LOOKED AT THE ENG GAUGES AND NOTED: OIL PRESSURE; AND OIL TEMP WERE BOTH STABLE AT APPROPRIATE NUMBERS. EGT GAUGE SHOWED A MAX FULL SCALE DEFLECTION; AND FUEL FLOW WAS FLUCTUATING BTWN 10 GPH AND 15 GPH. I WAS THE PF AT THE TIME; SO I KEPT CTL OF THE ACFT. SINCE WE WERE IN THE TFC PATTERN I ELECTED TO RETURN FOR A LNDG. WHILE FLYING THE DOWNWIND I ADJUSTED THE PWR TO 1500 RPM. THE VIBRATIONS DECREASED AND THE ENG RAN SMOOTHER. I EXECUTED A CAUTIONARY LNDG WITH PWR; THE REST OF APCH AND LNDG WERE UNEVENTFUL. WE TAXIED AND SHUT THE ACFT DOWN. UPON INSPECTION OF THE ACFT I NOTED THAT THE FORWARD L CYLINDER (WHEN REFING THE PLT'S SEAT) HAD A BROKEN FUEL INJECTOR LINE. THE LINE HAD SEPARATED ABOUT AN INCH ABOVE WHERE THE LINE CONNECTED TO THE CYLINDER. I ALSO NOTED THAT FUEL WAS DRIPPING OUT OF THE LINE ONTO THE ENG. DURING THE EVENT I ELECTED TO KEEP THE ENG RUNNING. I NOTICED THAT THE OIL TEMP AND PRESSURE WERE AT NORMAL LEVELS; AND WHEN I DECREASED THE RPM THE EGT CAME TO A NORMAL LEVEL. HAD I OBSERVED UNSAFE LEVELS IN ALL 3 GAUGES I WOULD HAVE SHUT AND SECURED THE ENG WHILE SETTING UP FOR A LNDG AT CDK.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.