Greetings
I need some help diagnosing an engine issue. Background info: RV-7A, IO-360B1B (vertical induction) Aerosport power engine built from ECI parts, Whirlwind 200RV constant speed prop, AFP fuel injection, dual p-mags, GRT EFIS, and EIS.
Lately I have noticed an in-flight change in my engine performance that seems to spontaneously show itself after anywhere from 1/2 to 1 hour of flight time during cruising operations. Today I went up and tried to quantify things a little bit. After normal preflight, startup and run up, departed airport and climbed out with WOT, full rich, and just short of max RPM, somehwere around 2650. After 9 minutes of flight and at 8500 feet, I level off, cut my RPM to 2300, and do the big mixture pull to LOP. Everything normal at this point, and I am fat dumb and happy, because my no tail wind ground speed is 185-187 mph with about 7.2 gph fuel flow, and the EFIS says that means over 25 mpg. Cant beat that with a stick. CHTs 1-4 stabilize at 325, 345, 373, 370 while OAT is 57 degrees F. Biit of a spread from high to low there, and I plan at adding an air dams in front of #1 and #2, but just havent done it yet, and anyway, these numbers are what constitute 'normal' for me over the last three years, taking into account OAT variations.
OK, so far so good. But after about 30 minutes of hands-off autopilot flying today, and no changes to anything by me other than very minor tweaks to the mixture to keep it at 7.2 GPH, my numbers and performance suddenly change. CHTs drop by 25 to 30 degrees across the board, EGTs drop 30-45 degrees, my ground speed drops (dont have a hard value for that, but something like 15 mph) and the engine no longer runs smooth at 7.2 gph; I have to richen up to somewhere around 8.3-8.5 gph. I dont like the power loss, and certainly not the increased fuel flow to get things running right again, but other than that, the engine seems to keep running ok - I dont get the feeling its gonna quit on me.
These symptoms are now happening on a regular basis, although the flight time at which it happens isnt exactly the same from flight to flight. It occurred to me that perhaps I was losing the use of one p-mag? Gas was running low, so I didnt get a chance to fully check this out today, but during my less than full throttle, probably ROP descent, I did cut first the the left p-mag, then the right p-mag, and saw all the EGTs go up each time, so they both were working at that point, and they both functioned during pre-takeoff run up, so that theory seems unlikely.
What else could be happening here? Maybe some kind of induction leak that only shows up after the engine reaches normal operating temps? I dont get it. Any theories or trouble shooting advice?
thanks in advance
erich
I need some help diagnosing an engine issue. Background info: RV-7A, IO-360B1B (vertical induction) Aerosport power engine built from ECI parts, Whirlwind 200RV constant speed prop, AFP fuel injection, dual p-mags, GRT EFIS, and EIS.
Lately I have noticed an in-flight change in my engine performance that seems to spontaneously show itself after anywhere from 1/2 to 1 hour of flight time during cruising operations. Today I went up and tried to quantify things a little bit. After normal preflight, startup and run up, departed airport and climbed out with WOT, full rich, and just short of max RPM, somehwere around 2650. After 9 minutes of flight and at 8500 feet, I level off, cut my RPM to 2300, and do the big mixture pull to LOP. Everything normal at this point, and I am fat dumb and happy, because my no tail wind ground speed is 185-187 mph with about 7.2 gph fuel flow, and the EFIS says that means over 25 mpg. Cant beat that with a stick. CHTs 1-4 stabilize at 325, 345, 373, 370 while OAT is 57 degrees F. Biit of a spread from high to low there, and I plan at adding an air dams in front of #1 and #2, but just havent done it yet, and anyway, these numbers are what constitute 'normal' for me over the last three years, taking into account OAT variations.
OK, so far so good. But after about 30 minutes of hands-off autopilot flying today, and no changes to anything by me other than very minor tweaks to the mixture to keep it at 7.2 GPH, my numbers and performance suddenly change. CHTs drop by 25 to 30 degrees across the board, EGTs drop 30-45 degrees, my ground speed drops (dont have a hard value for that, but something like 15 mph) and the engine no longer runs smooth at 7.2 gph; I have to richen up to somewhere around 8.3-8.5 gph. I dont like the power loss, and certainly not the increased fuel flow to get things running right again, but other than that, the engine seems to keep running ok - I dont get the feeling its gonna quit on me.
These symptoms are now happening on a regular basis, although the flight time at which it happens isnt exactly the same from flight to flight. It occurred to me that perhaps I was losing the use of one p-mag? Gas was running low, so I didnt get a chance to fully check this out today, but during my less than full throttle, probably ROP descent, I did cut first the the left p-mag, then the right p-mag, and saw all the EGTs go up each time, so they both were working at that point, and they both functioned during pre-takeoff run up, so that theory seems unlikely.
What else could be happening here? Maybe some kind of induction leak that only shows up after the engine reaches normal operating temps? I dont get it. Any theories or trouble shooting advice?
thanks in advance
erich