Narrative:

At cruise an hour and a half into a 3 hour planned flight; when the engine monitor (EDM700) showed a spike in egt and a fall in cht on number 6 cylinder. [I] attempted to remedy by changing mixture; power settings; etc. To no avail. Condition continued to deteriorate and engine began to vibrate. Reduced power to 20 inches mp (flight idle to maintain power and keep the engine warm). Used GPS to locate the closest airport and landed uneventfully. As it was a holiday; there was no mechanic available to investigate or repair. The next morning; the mechanic removed and cleaned the injector and spark plug for number 6 cylinder. Ground run showed everything good so took off to complete trip. Climbed out northeast to 9;500 ft; as I passed 8;000 or so same condition as before with number 5 and then number 3 cylinder. Did a 180 and returned. Removed and cleaned all 6 injectors; together with rails and lines. [I] drained fuel from sumps. [I] noted dirt in main sump drain. Both wing tanks showed no matter. Removed gascolator; [I] noted sludge and dirt. Cleaned; replaced gaskets and ran more fuel through all lines. Ground ran for 10 minutes at high idle (15 inches). Took off to complete trip; I made it to about the same location and noted cylinders 2; 3; and 5 with problems. Returned and cleaned all six injectors; rails and lines again. Ground ran and took off and orbited. I was able to reach 9;500 but by the time I set it up for cruise; noted a problem with number 5 cylinder. Returned and cleaned all injectors; lines and rails. At each of these past trips; fuel samples were taken with no particulate matter noted. Took off and orbited again. Climbed to 9;500 ft set up for cruise flew for 10 minutes and noted a small issue with number 6 cylinder. Returned and cleaned all injectors on that side (left). Took off and orbited at 9;500 ft set up for cruise; flew for 10 minutes and noted no issues. [We] successfully completed trip. Contacted FBO where the last fuel purchase was made. They reported several purchases at the self-serve both before and after me with no other issues reported. They reported that they sample the tank daily. Aircraft had previously been flown for 3.7 hours; 2 days prior with no problems. Aircraft is flown regularly. It is hangared at home base but spent a large part of the winter outside in new england. A drain that operates from the cockpit with no easy method of collecting the fuel seems to be an issue. Operating manual says to utilize the cockpit activated drain on every 3rd or 4th flight. Subsequent experienced mooney maintenance had told me to do it every flight. The sample drained onto the ramp will tell you if there is water but nothing else.

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Original NASA ASRS Text

Title: M20 pilot reports diverting for a rough running engine. The number six cylinder spark plugs and fuel injector is cleaned by a mechanic but the problem returns. Contaminants are found in the fuel and three more injector cleanings and three more test flights are required before the problem is cleared up.

Narrative: At cruise an hour and a half into a 3 hour planned flight; when the engine monitor (EDM700) showed a spike in EGT and a fall in CHT on number 6 cylinder. [I] attempted to remedy by changing mixture; power settings; etc. to no avail. Condition continued to deteriorate and engine began to vibrate. Reduced power to 20 inches MP (flight idle to maintain power and keep the engine warm). Used GPS to locate the closest airport and landed uneventfully. As it was a holiday; there was no mechanic available to investigate or repair. The next morning; the Mechanic removed and cleaned the injector and spark plug for number 6 cylinder. Ground run showed everything good so took off to complete trip. Climbed out northeast to 9;500 FT; as I passed 8;000 or so same condition as before with number 5 and then number 3 cylinder. Did a 180 and returned. Removed and cleaned all 6 injectors; together with rails and lines. [I] drained fuel from sumps. [I] noted dirt in main sump drain. Both wing tanks showed no matter. Removed gascolator; [I] noted sludge and dirt. Cleaned; replaced gaskets and ran more fuel through all lines. Ground ran for 10 minutes at high idle (15 inches). Took off to complete trip; I made it to about the same location and noted cylinders 2; 3; and 5 with problems. Returned and cleaned all six injectors; rails and lines again. Ground ran and took off and orbited. I was able to reach 9;500 but by the time I set it up for cruise; noted a problem with number 5 cylinder. Returned and cleaned all injectors; lines and rails. At each of these past trips; fuel samples were taken with no particulate matter noted. Took off and orbited again. Climbed to 9;500 FT set up for cruise flew for 10 minutes and noted a small issue with number 6 cylinder. Returned and cleaned all injectors on that side (left). Took off and orbited at 9;500 FT set up for cruise; flew for 10 minutes and noted no issues. [We] successfully completed trip. Contacted FBO where the last fuel purchase was made. They reported several purchases at the self-serve both before and after me with no other issues reported. They reported that they sample the tank daily. Aircraft had previously been flown for 3.7 hours; 2 days prior with no problems. Aircraft is flown regularly. It is hangared at home base but spent a large part of the winter outside in New England. A drain that operates from the cockpit with no easy method of collecting the fuel seems to be an issue. Operating manual says to utilize the cockpit activated drain on every 3rd or 4th flight. Subsequent experienced Mooney Maintenance had told me to do it every flight. The sample drained onto the ramp will tell you if there is water but nothing else.

Data retrieved from NASA's ASRS site 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.