Narrative:

In cruise at 9500 ft; noticed fluctuation in fuel pressure. Needle moved erratically for almost a minute then began to fall slowly. Simultaneously; egt decreased 50 degrees and engine began to run roughly. Adjusted mixture turned towards an airport that I had just passed and tuned tower frequency. Fuel pressure and egt stabilized momentarily; but engine remained slightly rough. After another minute; fuel pressure began to drop again despite use of manual boost pump; settling around 9 psi. Contacted tower and requested precautionary landing. [I] requested clearance to spiral down overhead the airport due to low fuel pressure indication and rough engine. Passed overhead the airport under power at approximately 3000 ft AGL into a high left downwind runway xx cleared to land. Landed without incident and taxied under own power to FBO before shutting down. A&P is disassembling the fuel pump; fuel servo; and manual boost pump to troubleshoot the cause of the problem. Comment on decision making: should have turned towards the nearby airport as soon as the fuel pressure and egt began to fail instead of holding course while observing the instruments for further information. (Could have orbited there while troubleshooting and informing tower of issue and intents.) comment on troubleshooting: fuel pressure had wavered during a flight a week before the reported flight. Main (system low point) filter was removed and found to be clogged. Replaced with a new filter; strained fuel before reported flight and found no contaminants. Assumed the problem was found and corrected.

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Original NASA ASRS Text

Title: A Pitts S1 Pilot declared an emergency and diverted for a rough running engine and low fuel pressure. The fuel pump; fuel line; fuel filter and wobble pump were all replaced or rebuilt.

Narrative: In cruise at 9500 FT; noticed fluctuation in fuel pressure. Needle moved erratically for almost a minute then began to fall slowly. Simultaneously; EGT decreased 50 degrees and engine began to run roughly. Adjusted mixture turned towards an airport that I had just passed and tuned tower frequency. Fuel pressure and EGT stabilized momentarily; but engine remained slightly rough. After another minute; fuel pressure began to drop again despite use of manual boost pump; settling around 9 PSI. Contacted Tower and requested precautionary landing. [I] requested clearance to spiral down overhead the airport due to low fuel pressure indication and rough engine. Passed overhead the airport under power at approximately 3000 FT AGL into a high left downwind Runway XX cleared to land. Landed without incident and taxied under own power to FBO before shutting down. A&P is disassembling the fuel pump; fuel servo; and manual boost pump to troubleshoot the cause of the problem. Comment on decision making: should have turned towards the nearby airport as soon as the fuel pressure and EGT began to fail instead of holding course while observing the instruments for further information. (Could have orbited there while troubleshooting and informing Tower of issue and intents.) Comment on troubleshooting: fuel pressure had wavered during a flight a week before the reported flight. Main (system low point) filter was removed and found to be clogged. Replaced with a new filter; strained fuel before reported flight and found no contaminants. Assumed the problem was found and corrected.

Data retrieved from NASA's ASRS site as of April 2012 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.