Jeff R
Well Known Member
I have been flying my RV-9A about 10 hours now, but the engine is making me nervous.
Here is the background information:
The engine is a YIO-320-D1A obtained new in mid-2008. It has been mounted to my airframe since late 2008. I used desiccant plugs for rust prevention. I have the Precision Airmotive Silver Hawk experimental fuel injection system, and I run a PMAG with BR8EIS auto plugs on the top and a standard Slick mag with standard aviation plugs on the bottom.
Ever since the first engine start the engine has run rough on the ground. We have adjusted the idle for about 750 RPM, but the RPM will vary and drop down below 500 (which is why we have a somewhat high idle speed). I have most always leaned aggressively on the ground to peak RPM to minimize plug fouling.
However, when doing a mag check at 1700, I often see drops exceeding 250 RPM, even 300, which occurs on both the PMAG and Slick. Sometimes, if I lean it out at runup, the mag drop will be around 150 - 200 on each. Sometimes when going to idle the engine will sputter to under 500 RPM and has even died on several occasions.
I can find no induction leaks. We have ried to set the mixture adjustment to give about a 50 RPM drop, though the adjustment is tricky as the RPM is often so variable, so the RPM increase might be closer to 100.
In flight, the engine has been perfect. I have been nervous about pulling it to idle, but it hasn't skipped a beat and has run flawlessly. I went up this morning and was going to go up again this afternoon but aborted due to the high mag drops and failure to clear it out with leaning during runup. (Drops were around 200 this morning - which is high, but 300 is well beyond by comfort range).
Pulling a top plug this afternoon showed lots of black (no fouling), which seems to indicate a too-rich mixture.
I have tried BR8EX and BR9EIX plugs with no noticeable difference. Taking plugs out and cleaning them makes no difference.
With equally bad performance on both mag and Pmag it appears problems in the electrical system can be ruled out. We have checked fuel low to the injectors and all looks fine, so the pump system can be ruled out. I have tried running with the boost pump on and off, where the pressure is 29 psi on and 27 psi with boost pump off. Not much difference. I also checked the filter at the throttle body and it was clean.
Fuel burn seems a bit high perhaps. Today I was burning 9.9 gph at 2070 RPM at 22.6 MP. The Skyview said the power was 63%. This was at pretty much full rich at 1,600 feet with a DA of about 3,000 ft. Isn't this a bit high?
I am wondering if the throttle body is putting out too much fuel. Even so, I can lean the mixture on the ground and the RPM will still vary by 100 RPM and more.
Any ideas?
Here is the background information:
The engine is a YIO-320-D1A obtained new in mid-2008. It has been mounted to my airframe since late 2008. I used desiccant plugs for rust prevention. I have the Precision Airmotive Silver Hawk experimental fuel injection system, and I run a PMAG with BR8EIS auto plugs on the top and a standard Slick mag with standard aviation plugs on the bottom.
Ever since the first engine start the engine has run rough on the ground. We have adjusted the idle for about 750 RPM, but the RPM will vary and drop down below 500 (which is why we have a somewhat high idle speed). I have most always leaned aggressively on the ground to peak RPM to minimize plug fouling.
However, when doing a mag check at 1700, I often see drops exceeding 250 RPM, even 300, which occurs on both the PMAG and Slick. Sometimes, if I lean it out at runup, the mag drop will be around 150 - 200 on each. Sometimes when going to idle the engine will sputter to under 500 RPM and has even died on several occasions.
I can find no induction leaks. We have ried to set the mixture adjustment to give about a 50 RPM drop, though the adjustment is tricky as the RPM is often so variable, so the RPM increase might be closer to 100.
In flight, the engine has been perfect. I have been nervous about pulling it to idle, but it hasn't skipped a beat and has run flawlessly. I went up this morning and was going to go up again this afternoon but aborted due to the high mag drops and failure to clear it out with leaning during runup. (Drops were around 200 this morning - which is high, but 300 is well beyond by comfort range).
Pulling a top plug this afternoon showed lots of black (no fouling), which seems to indicate a too-rich mixture.
I have tried BR8EX and BR9EIX plugs with no noticeable difference. Taking plugs out and cleaning them makes no difference.
With equally bad performance on both mag and Pmag it appears problems in the electrical system can be ruled out. We have checked fuel low to the injectors and all looks fine, so the pump system can be ruled out. I have tried running with the boost pump on and off, where the pressure is 29 psi on and 27 psi with boost pump off. Not much difference. I also checked the filter at the throttle body and it was clean.
Fuel burn seems a bit high perhaps. Today I was burning 9.9 gph at 2070 RPM at 22.6 MP. The Skyview said the power was 63%. This was at pretty much full rich at 1,600 feet with a DA of about 3,000 ft. Isn't this a bit high?
I am wondering if the throttle body is putting out too much fuel. Even so, I can lean the mixture on the ground and the RPM will still vary by 100 RPM and more.
Any ideas?