I had posted a previous thread about a slightly rough running engine (not enough that passengers would notice, just a bit off) http://www.piperforum.com/showthread.php?t=12974
Through diagnostics with the engine management, I think I have that chased to leaks in the intake manifold (the soft tubes look pretty worn and cracked). I also checked the fuel screen in the belly sump just to be sure.
I took it up for another diagnostic flight today to re-confirm my previous results on the E.M. but I ran into some other symptoms that I need to chase.
1. Before start priming, the primer was completely dry. It took a dozen or more strokes before fuel was in the primer to pump. Sometimes I have noticed on a warm start (engine has run that day) that the primer is dry. Indicative of a leak in the primer? Our old PA28 rarely had an empty primer.
2. In cruise climb, at about 2500' I had a complete power failure for about 10 seconds (I think, felt like forever). With arsehole puckered firmly up into my throat, I confirmed I had correct fuel flow, and fuel pressure. Switched tanks and the power came back. Stayed over airport with sufficient altitude and switched back to "suspect tank" and ran hard with high fuel flows, and it ran perfect. Completed my EGT/fuel flow diagnostics over the next 15 minutes with no issues.
In all honestly it felt like pulling the mixture to ICO, and then came back just as smooth. I had sumped the fuel at the tanks and the belly with no signs of water.
So, possible problems?:
- My first reaction is that I got a big slug of air in the fuel lines when cleaning the fuel filter that didn't make it all the way through the system in the run-up/idle. When I looked down at fuel flow, perhaps the air was in the carb, and past the transducer so perhaps fuel flow was now normal again as it pushed the fuel into the carb. The transducer is about 2-2.5 feet from the carb after the mechanical fuel pump. It also wasn't a quick warm-up and run-up; at least 10 minutes so I would have thought the fuel got all the way through the lines, but maybe not. Thank god it was 2500', not 100'
- As Don suggested prior with the rough feel, possible carb issue. But is there a carb issue that would cause momentary loss of power, that comes back without really making changes? (throttle and mixture were full forward and remained there).
- primer leaking is a source for air in the fuel system. While this would not help the smooth running situation, I couldn't see this completely cutting power and then being fine.
- If somehow both mags grounded simultaneously, I would have expected a big pop from raw fuel being pumped into the exhaust. She came back smooth.
Needless to say, I am at a bit of a loss. I am not a fan of just taking it to a mechanic and throwing money at a problem replacing random bits without a good idea of where to look for an issue (besides, we don't have a mech at the field). I haven't been able to re-create any rough running or power losses on the ground, so it is tough for a diagnosis anyways.
Comments, questions, insults?
Through diagnostics with the engine management, I think I have that chased to leaks in the intake manifold (the soft tubes look pretty worn and cracked). I also checked the fuel screen in the belly sump just to be sure.
I took it up for another diagnostic flight today to re-confirm my previous results on the E.M. but I ran into some other symptoms that I need to chase.
1. Before start priming, the primer was completely dry. It took a dozen or more strokes before fuel was in the primer to pump. Sometimes I have noticed on a warm start (engine has run that day) that the primer is dry. Indicative of a leak in the primer? Our old PA28 rarely had an empty primer.
2. In cruise climb, at about 2500' I had a complete power failure for about 10 seconds (I think, felt like forever). With arsehole puckered firmly up into my throat, I confirmed I had correct fuel flow, and fuel pressure. Switched tanks and the power came back. Stayed over airport with sufficient altitude and switched back to "suspect tank" and ran hard with high fuel flows, and it ran perfect. Completed my EGT/fuel flow diagnostics over the next 15 minutes with no issues.
In all honestly it felt like pulling the mixture to ICO, and then came back just as smooth. I had sumped the fuel at the tanks and the belly with no signs of water.
So, possible problems?:
- My first reaction is that I got a big slug of air in the fuel lines when cleaning the fuel filter that didn't make it all the way through the system in the run-up/idle. When I looked down at fuel flow, perhaps the air was in the carb, and past the transducer so perhaps fuel flow was now normal again as it pushed the fuel into the carb. The transducer is about 2-2.5 feet from the carb after the mechanical fuel pump. It also wasn't a quick warm-up and run-up; at least 10 minutes so I would have thought the fuel got all the way through the lines, but maybe not. Thank god it was 2500', not 100'
- As Don suggested prior with the rough feel, possible carb issue. But is there a carb issue that would cause momentary loss of power, that comes back without really making changes? (throttle and mixture were full forward and remained there).
- primer leaking is a source for air in the fuel system. While this would not help the smooth running situation, I couldn't see this completely cutting power and then being fine.
- If somehow both mags grounded simultaneously, I would have expected a big pop from raw fuel being pumped into the exhaust. She came back smooth.
Needless to say, I am at a bit of a loss. I am not a fan of just taking it to a mechanic and throwing money at a problem replacing random bits without a good idea of where to look for an issue (besides, we don't have a mech at the field). I haven't been able to re-create any rough running or power losses on the ground, so it is tough for a diagnosis anyways.
Comments, questions, insults?
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