Toobuilder
Well Known Member
I need some help! Flew my buddy's -8 for 1.7 today and had a great time exept for the last 3 minutes... After flying all over the countryside and doing landings at multiple airports, it was only after I entered the pattern at my home base that trouble began. As I pulled the power back to idle, the engine went very rough and lost significant power. It acted very much like my Hiperbipe does every time I run a tank dry (normal ops on a long cross country). So I swithched tanks (both had plenty of gas) and hit the boost pump (good pressure) all to no avail. Did a quick mag check on downwind and pulled the throttle to idle (as normal) for a power off pattern to land. At idle, it SEEMED to carry a bit more thrust than normal, so I'm thinking I'll need to kill it on short final with the mixture or ignition. Seems ok after all so I land the thing no problem. Once stopped on the runway, does not want to idle, but at anything off the idle stop, it runs up to 2000 RPM with lots of popping out the exhaust and roughness. Cylinder #3 EGT is almost nothing, so it has given up.
Once at the hangar my brain is trying to comprehend the problem so I start checking stuff that I know I can verify:
Comperession
Fuel flow and injector nozzle pattern check
Ignition timing
Intake leaks
Throttle butterfly loose/induction blockage
Plugs
With all these good, I feel it's safe to run the engine on the ground without much chance of doing any damage to the really expensive stuff. With the tail tied down, I run the engine and it is still running the same (of course), but I can monitor EGT and so forth. Long story short, it is running very, very fat, with lots of smoke, popping, sputtering and roughness. The mixture will change the behavior somewhat, but at best, it barely runs at part throttle, let alone idle. It drops a cylinder or two due to plug fouling, and they come back with new plugs, so it seems fairly obvious to me that the servo has failed somehow and there is simply a super rich mixture.
Now I am an A&P, but I don't have much experience troubleshooting Bendix injection other than flying behind the same system on my Hiperbipe for hundreds of troublefree hours. Am I missing anything? Can I replace a simple diaphragm and be on my way, or am I looking at an overhaul? In theory, this unit only has 388 hours on it, but it was overhauled before 1988, then not flown until 2003. I suppose there are some rubber parts that didn?t like sitting for all those years without use.
Any help is much appreciated!
Once at the hangar my brain is trying to comprehend the problem so I start checking stuff that I know I can verify:
Comperession
Fuel flow and injector nozzle pattern check
Ignition timing
Intake leaks
Throttle butterfly loose/induction blockage
Plugs
With all these good, I feel it's safe to run the engine on the ground without much chance of doing any damage to the really expensive stuff. With the tail tied down, I run the engine and it is still running the same (of course), but I can monitor EGT and so forth. Long story short, it is running very, very fat, with lots of smoke, popping, sputtering and roughness. The mixture will change the behavior somewhat, but at best, it barely runs at part throttle, let alone idle. It drops a cylinder or two due to plug fouling, and they come back with new plugs, so it seems fairly obvious to me that the servo has failed somehow and there is simply a super rich mixture.
Now I am an A&P, but I don't have much experience troubleshooting Bendix injection other than flying behind the same system on my Hiperbipe for hundreds of troublefree hours. Am I missing anything? Can I replace a simple diaphragm and be on my way, or am I looking at an overhaul? In theory, this unit only has 388 hours on it, but it was overhauled before 1988, then not flown until 2003. I suppose there are some rubber parts that didn?t like sitting for all those years without use.
Any help is much appreciated!