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My PA28-180's going in for annual soon, and this year my squawk list is small. However, there is one situation that I'm tracking that I'm unsure about. I think it could be an indication of trouble, or it could be a ghost that I'm simply imagining. So I solicit opinions from the group.
I have some indications from my engine monitor that CHTs are reading higher than historically, and fuel flow rates are reading lower than historically, during full-power regimes like takeoffs and climbs to altitude. I am not 100% confident in those readings, for various reasons that would make for a long story. However, if they're real, then I wonder if it's an indication of a problem with the engine-driven fuel pump, or the carburetor.
RPMs still seem to be normal during those operating regimes, so the engine appears to be making the expected power. If I did not have an engine monitor, I would not have any other symptoms to cause me concern...which is why I wonder if I'm imagining a problem.
As a test, I have tried turning on my boost pump during climbs to see if CHTs come down. My thinking is that if the engine-driven pump was degrading, I might see the CHTs drop a bit from the additional fuel provided by the boost pump. (Because the boost pump bypasses the FF sensor, I can't really see what happens to total fuel flow when both pumps are on, so watching CHTs is the only way to maybe derive that more fuel is flowing.) I see no obvious change in CHTs when the boost pump is on.
If there is a real fuel flow problem, then perhaps another place to check would be the carburetor. Maybe some problem with the economizer/enrichment circuit at WOT?
The engine has about 1100 hrs since last overhaul (12 years ago). Logs say "carburetor cleaned and float adjusted" as part of that work. I've skimmed back but didn't see any reference to the engine pump in the last 1500 hours or so (15 years), so I'm not sure when it might have been touched last.
There are no indications of fuel leaks anywhere.
So, should I:
I have some indications from my engine monitor that CHTs are reading higher than historically, and fuel flow rates are reading lower than historically, during full-power regimes like takeoffs and climbs to altitude. I am not 100% confident in those readings, for various reasons that would make for a long story. However, if they're real, then I wonder if it's an indication of a problem with the engine-driven fuel pump, or the carburetor.
RPMs still seem to be normal during those operating regimes, so the engine appears to be making the expected power. If I did not have an engine monitor, I would not have any other symptoms to cause me concern...which is why I wonder if I'm imagining a problem.
As a test, I have tried turning on my boost pump during climbs to see if CHTs come down. My thinking is that if the engine-driven pump was degrading, I might see the CHTs drop a bit from the additional fuel provided by the boost pump. (Because the boost pump bypasses the FF sensor, I can't really see what happens to total fuel flow when both pumps are on, so watching CHTs is the only way to maybe derive that more fuel is flowing.) I see no obvious change in CHTs when the boost pump is on.
If there is a real fuel flow problem, then perhaps another place to check would be the carburetor. Maybe some problem with the economizer/enrichment circuit at WOT?
The engine has about 1100 hrs since last overhaul (12 years ago). Logs say "carburetor cleaned and float adjusted" as part of that work. I've skimmed back but didn't see any reference to the engine pump in the last 1500 hours or so (15 years), so I'm not sure when it might have been touched last.
There are no indications of fuel leaks anywhere.
So, should I:
- Dig into this further? If so, what's the right path of investigation to follow? Or...
- Leave well enough alone until I get clearer indications of a problem?
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