I've taken my plane in now several times over the past few months to have the same issue fixed. The problem is that it seems to never replicate itself while my mechanic is looking at it. The issue is that while in flight (and sometimes on the ground), my fuel flow gauge starts fluctuating up to a maximum of plus or minus 1 to 2 gallons per hour. When it fluctuates, I can feel a very slight power differences during flight so I know it is more than just the gauge. I got so frustrated, I said the hell with it and just sent the plane in for annual. Well, now my plane is done with annual and my mechanic still did not find anything wrong. For a bit of background, my engine is slightly over mid-life SMOH, although TOH about 400 hours ago. I've had my fuel servo overhauled less than a year ago thinking that would help (it seems to have lessened, but that could be in my head). The problem is intermittent, so I only observe this occurring on average about once per month, flying nearly every weekend. Here are a few things my mechanic has recommended and how I've responded. I'd love to hear your thoughts or other recommendations, although if they are beyond operating procedure, I'm the furthest thing from a mechanic so doing my own work is a out of the question.
Mechanic recommendation: Don't lean the engine at all until above 5,000 MSL. He claims that many pilots around the Chicago area do this given we are fairly close to sea level.
My responses: He gave me this recommendation during annual so I have to try it out. I have a digital EGT/CHT, although it is only single probe. My practice that I've been using is leaning to peak, even I fly to 3,000 MSL, and then richen to be about 75 degrees below peak.
Mechanic recommendation: I should richen mixture to more than 100 degrees below peak because it is a single probe EGT/CHT. He's telling me a common symptom causing this is if the one of the cylinders is burning to lean/hot causing (misfires?).
My response: Haven't tried this method out either since the recommendation also came during annual.
Mechanic recommendation: Water may be getting in the fuel, also a common symptom that would cause the fuel flow gauge to go crazy and affect power. If water is in fact getting in the fuel, he recommends in the winter time to add isopropyl alcohol in the fuel, one pint per tank on a full tank. He says the flight schools used to have water getting in the tanks and after calling up Lycomming, they were the ones that recommended this treatment provided the mixture remains under 1%. He claims they never had problem after that. (FYI - there apparently is a service bulletin from Lycomming that makes this practice permissible)
My response: I don't really want to be adding crap to my fuel. Also, I do a proper pre-flight with sump and have very rarely seen water in my tanks through the sump (maybe once or twice, in the past year). My mechanic says that it is possible that the water swirls around in the tanks and not making it to the sump which is why I'm not seeing it during preflight.
Another pilot buddy's recommendation believing it could also be water: Replace the fuel cap gasket as he replaces his every few years.
My response: Ordered and replaced the seals myself last night, so I have yet to see whether that helps or not. The old seals didn't look that great, but who knows if that was the issue.
Same pilot buddy's recommendation: My recently overhauled fuel servo went bad.
My response: Talked to my mechanic and said that with the shop he uses over the past 10 years, he's never seen a poorly overhauled or faulty parts relating to fuel servo. Furthermore, nothing is leaking and the engine kills on command when I lean out the mixture (prior to the overhaul, it did not, indicating it was leaking). He says there is nothing indicating that is problem and I'd likely be throwing away money to take it back off for a reinspection.
Please provide any input on anything I've provided or my operating procedures.
Mechanic recommendation: Don't lean the engine at all until above 5,000 MSL. He claims that many pilots around the Chicago area do this given we are fairly close to sea level.
My responses: He gave me this recommendation during annual so I have to try it out. I have a digital EGT/CHT, although it is only single probe. My practice that I've been using is leaning to peak, even I fly to 3,000 MSL, and then richen to be about 75 degrees below peak.
Mechanic recommendation: I should richen mixture to more than 100 degrees below peak because it is a single probe EGT/CHT. He's telling me a common symptom causing this is if the one of the cylinders is burning to lean/hot causing (misfires?).
My response: Haven't tried this method out either since the recommendation also came during annual.
Mechanic recommendation: Water may be getting in the fuel, also a common symptom that would cause the fuel flow gauge to go crazy and affect power. If water is in fact getting in the fuel, he recommends in the winter time to add isopropyl alcohol in the fuel, one pint per tank on a full tank. He says the flight schools used to have water getting in the tanks and after calling up Lycomming, they were the ones that recommended this treatment provided the mixture remains under 1%. He claims they never had problem after that. (FYI - there apparently is a service bulletin from Lycomming that makes this practice permissible)
My response: I don't really want to be adding crap to my fuel. Also, I do a proper pre-flight with sump and have very rarely seen water in my tanks through the sump (maybe once or twice, in the past year). My mechanic says that it is possible that the water swirls around in the tanks and not making it to the sump which is why I'm not seeing it during preflight.
Another pilot buddy's recommendation believing it could also be water: Replace the fuel cap gasket as he replaces his every few years.
My response: Ordered and replaced the seals myself last night, so I have yet to see whether that helps or not. The old seals didn't look that great, but who knows if that was the issue.
Same pilot buddy's recommendation: My recently overhauled fuel servo went bad.
My response: Talked to my mechanic and said that with the shop he uses over the past 10 years, he's never seen a poorly overhauled or faulty parts relating to fuel servo. Furthermore, nothing is leaking and the engine kills on command when I lean out the mixture (prior to the overhaul, it did not, indicating it was leaking). He says there is nothing indicating that is problem and I'd likely be throwing away money to take it back off for a reinspection.
Please provide any input on anything I've provided or my operating procedures.
