Brent Hoops
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- Jul 14, 2019
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New to the forum here and, of course, was drawn in by a desire to solve my latest mechanical mystery. I have a 1966 PA-32-260 with about 2250 TT and 250 SMOH. On my last two flights there's been a disconcerting and intermittent "hiccup" to the engine in cruise flight. It lasts maybe half a second and is just long enough to hear the engine sort of skip and even feel the plane momentarily slow down. As soon as the problem is noticed, it passes and the plane goes back to cruise flight for an indeterminable amount of time before happening again. All engine gauges look good before, after, and during. Fuel pressure needle doesn't seem to move. EGT is around 14, oil temp about 215, and oil pressure basically maxed out. Engine was running with about 10 qts. oil in it.
My first inclination was carb ice, and outside conditions were ripe for it on both days - high humidity and OAT around 70F. However, I've flown in similar conditions many times and never had a problem. Pulling the carb heat maybe made the problem go away for a while, but it's hard to say for sure as I didn't want to leave it on for more than about 5 minutes. I've read that if there is carb ice, pulling the carb heat should make the problem seem worse before it gets better, and that didn't happen. At one point I left the carb heat on for 15 minutes and still eventually got the same engine sputter. In that instance I decided to land about 1 hr into a 3 hr flight to look things over. After removing the top cowling, scratching my head, and talking with the A&P for about 20 minutes, I took off again and had no issues for the rest of the flight, although the problem did resurface toward the end of my return flight home later in the day. Logically, I would guess that I had some carb ice when I made the unplanned stop and the 20 minutes of head scratching allowed it to melt and clear on the ground. The carb heat cable was inspected and seems to be operating as expected during engine run-up.
From what I've read and heard, the carb heat is usually not needed on an O-540 engine due the carburetor's close proximity to the oil pan. I'd like to know if anyone else on the forum has had carb ice issues in a similar plane and what other problems I may be overlooking. The current plan with the local A&P is take apart the carburetor next week and look for abnormalities. Thanks in advance for any replies/advice.
My first inclination was carb ice, and outside conditions were ripe for it on both days - high humidity and OAT around 70F. However, I've flown in similar conditions many times and never had a problem. Pulling the carb heat maybe made the problem go away for a while, but it's hard to say for sure as I didn't want to leave it on for more than about 5 minutes. I've read that if there is carb ice, pulling the carb heat should make the problem seem worse before it gets better, and that didn't happen. At one point I left the carb heat on for 15 minutes and still eventually got the same engine sputter. In that instance I decided to land about 1 hr into a 3 hr flight to look things over. After removing the top cowling, scratching my head, and talking with the A&P for about 20 minutes, I took off again and had no issues for the rest of the flight, although the problem did resurface toward the end of my return flight home later in the day. Logically, I would guess that I had some carb ice when I made the unplanned stop and the 20 minutes of head scratching allowed it to melt and clear on the ground. The carb heat cable was inspected and seems to be operating as expected during engine run-up.
From what I've read and heard, the carb heat is usually not needed on an O-540 engine due the carburetor's close proximity to the oil pan. I'd like to know if anyone else on the forum has had carb ice issues in a similar plane and what other problems I may be overlooking. The current plan with the local A&P is take apart the carburetor next week and look for abnormalities. Thanks in advance for any replies/advice.
