Bubblehead
Well Known Member
I've been battling gremlins for 6 months on my engine. Every time I think I have things solved, the engine proves me wrong.
For about 6 months the engine would start fine, run fine, the plane would fly about the same speeds as always, but occasionally would start running rough and lose a little power. I'd try richening, leaning, mag checks, throttle back, throttle up, and sometimes it would get better and sometimes not.
For a while I thought it was dirt getting into injectors. I inspected the sleeves with a magnifying glass. Sometimes I'd find a little piece of dirt but usually not. Sometimes the problem got better only to later to reappear. I checked the fuel filter and fittings and never found anything in the filter and the fittings look good.
A month ago I pulled the magneto cap (dual mag system) and ignition wires and found a spot worn through the insulation to the conductor. I ordered a new harness and cap, but it has not arrived yet. I repaired the damaged area with silicone stretch-tape and carefully routed the wires. For a few flights things were smoother but Sunday I flew to Midland, TX from Ft Worth and back to visit family and it acted up a little going and a lot coming home. 1 hr 15 mins is a long time when an engine is running intermittently rough.
For most of the 6 months I did not have a way to record data from the EIS, but before leaving Sunday I plugged in my EIS Mate and recorded the 3 hours of flight time. I graphed EGT and fuel flow and noticed that EGTs are fluctuating about 50 to 100 degrees and fuel flow is fluctuating about 1 gph. I noticed that while in flight yesterday but did not realize how bad it was.
I went back over data from flights last spring and last fall, and in the fall it varied a little, and got a lot worse in the spring, but not as bad as it is now.
I noticed one other strange indication yesterday. Usually when I turn my boost pump on or off the fuel flow changes about 0.3 gph and then within a few seconds returns to the same fuel flow as before. Yesterday it jumped up about 1 gph and took a minute to return to the old flow rate.
Does it sounds like the fuel injection servo or spider might be bad? It has 600 hours on it on this airplane but I'm not sure how much total time it has on it. My next guess is mechanical fuel pump is going bad.
I need to call Don at Airflow and get his opinion but I thought I'd start here and learn more before taking some of his time.
One additional piece of data. I just did a little statistical look at the cruise portion of the flight from Midland, TX to Ft Worth, TX.
Cylinders 1 and 3 had the biggest variation of EGT temperatures with a standard deviation of 23.9 and 22.3 respectively compared to 9.3 and 11.9 for cylinders 2 and 4. Whatever is causing this seems to be affecting the right side cylinders more than the left side.
Fuel flow varied from 7.7 to 9.2 gph. Not sure why it drifted up to 9.2 but it did and I then leaned back to about 8.5.
For about 6 months the engine would start fine, run fine, the plane would fly about the same speeds as always, but occasionally would start running rough and lose a little power. I'd try richening, leaning, mag checks, throttle back, throttle up, and sometimes it would get better and sometimes not.
For a while I thought it was dirt getting into injectors. I inspected the sleeves with a magnifying glass. Sometimes I'd find a little piece of dirt but usually not. Sometimes the problem got better only to later to reappear. I checked the fuel filter and fittings and never found anything in the filter and the fittings look good.
A month ago I pulled the magneto cap (dual mag system) and ignition wires and found a spot worn through the insulation to the conductor. I ordered a new harness and cap, but it has not arrived yet. I repaired the damaged area with silicone stretch-tape and carefully routed the wires. For a few flights things were smoother but Sunday I flew to Midland, TX from Ft Worth and back to visit family and it acted up a little going and a lot coming home. 1 hr 15 mins is a long time when an engine is running intermittently rough.
For most of the 6 months I did not have a way to record data from the EIS, but before leaving Sunday I plugged in my EIS Mate and recorded the 3 hours of flight time. I graphed EGT and fuel flow and noticed that EGTs are fluctuating about 50 to 100 degrees and fuel flow is fluctuating about 1 gph. I noticed that while in flight yesterday but did not realize how bad it was.
I went back over data from flights last spring and last fall, and in the fall it varied a little, and got a lot worse in the spring, but not as bad as it is now.
I noticed one other strange indication yesterday. Usually when I turn my boost pump on or off the fuel flow changes about 0.3 gph and then within a few seconds returns to the same fuel flow as before. Yesterday it jumped up about 1 gph and took a minute to return to the old flow rate.
Does it sounds like the fuel injection servo or spider might be bad? It has 600 hours on it on this airplane but I'm not sure how much total time it has on it. My next guess is mechanical fuel pump is going bad.
I need to call Don at Airflow and get his opinion but I thought I'd start here and learn more before taking some of his time.
One additional piece of data. I just did a little statistical look at the cruise portion of the flight from Midland, TX to Ft Worth, TX.
Cylinders 1 and 3 had the biggest variation of EGT temperatures with a standard deviation of 23.9 and 22.3 respectively compared to 9.3 and 11.9 for cylinders 2 and 4. Whatever is causing this seems to be affecting the right side cylinders more than the left side.
Fuel flow varied from 7.7 to 9.2 gph. Not sure why it drifted up to 9.2 but it did and I then leaned back to about 8.5.
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