ColoRv
Well Known Member
Good Morning VAF'rs
I've been chasing an issue for a few months now, thought I found the smoking gun a couple of times but alas it still happens.
All was well for first 60 hours, then this issue showed up. If I let the plane sit for 12 hours or more I get an odd occurrence on start up. Crack throttle, mixture rich, boost pump 5 seconds... It fires up normally, runs great for 30 seconds or so then a cylinder drops off. Idle goes up a couple hundred RPM, EGT on that cylinder plummets, CHT starts falling and the engine shakes like a dog after a swim. 30 seconds or so and the cylinder comes back and she runs great from there on out. Normal run up, perfect in flight. Hot starts are normal. Switching Pmags off one at a time has no affect, EICommander says Pmags running normally. It only does this after sitting overnight or more.
The cylinder that drops out isn't always the same cylinder. Has been #1, #3 or currently #4. This leads us to believe it's fuel related and I'm getting air in the fuel line somewhere and that slug of air kills a cylinder until fuel arrives. What I am struggling to wrap my head around is why only one cylinder drops out when this happens, why it changes cylinders and why I'm not seeing any fuel leaks anywhere.
Here is what I've done so far:
Pulled all the injector nozzles and thoroughly cleaned them - no affect
Flow tested spider - seems fine
Pulled spider, checked diaphragm - looks fine, no holes
Pulled every fuel line from spider to tanks and checked the flares - no issues I can find.
Replaced lines from selector to firewall from my lines to professional built - desperation - no affect
Changed boost pump (had air leak when pressurized) - no affect
Capped the tank lines at the selector, pressurized the entire fuel system from spider to selector (10psi) and soapy water tested everything...no leaks I can see.
Spider and Servo (rsa5) were given an experimental overhaul by Airflow Performance prior to build and all was perfect for 60 hours.
Has anyone seen an issue like this before? A neighbor had a plane that would randomly drop a cylinder but only when hot and it turned out to be a bad fuel flow divider. I'm typically resistant to throwing new parts and a prayer at a problem....but this one has led me on quite the merry chase. I'm a heartbeat from replacing the entire fuel system. I want to fly my beautiful new plane without this annoying issue.
Any words of experience from the VAF masses?
Signed Desperate in Denver
I've been chasing an issue for a few months now, thought I found the smoking gun a couple of times but alas it still happens.
All was well for first 60 hours, then this issue showed up. If I let the plane sit for 12 hours or more I get an odd occurrence on start up. Crack throttle, mixture rich, boost pump 5 seconds... It fires up normally, runs great for 30 seconds or so then a cylinder drops off. Idle goes up a couple hundred RPM, EGT on that cylinder plummets, CHT starts falling and the engine shakes like a dog after a swim. 30 seconds or so and the cylinder comes back and she runs great from there on out. Normal run up, perfect in flight. Hot starts are normal. Switching Pmags off one at a time has no affect, EICommander says Pmags running normally. It only does this after sitting overnight or more.
The cylinder that drops out isn't always the same cylinder. Has been #1, #3 or currently #4. This leads us to believe it's fuel related and I'm getting air in the fuel line somewhere and that slug of air kills a cylinder until fuel arrives. What I am struggling to wrap my head around is why only one cylinder drops out when this happens, why it changes cylinders and why I'm not seeing any fuel leaks anywhere.
Here is what I've done so far:
Pulled all the injector nozzles and thoroughly cleaned them - no affect
Flow tested spider - seems fine
Pulled spider, checked diaphragm - looks fine, no holes
Pulled every fuel line from spider to tanks and checked the flares - no issues I can find.
Replaced lines from selector to firewall from my lines to professional built - desperation - no affect
Changed boost pump (had air leak when pressurized) - no affect
Capped the tank lines at the selector, pressurized the entire fuel system from spider to selector (10psi) and soapy water tested everything...no leaks I can see.
Spider and Servo (rsa5) were given an experimental overhaul by Airflow Performance prior to build and all was perfect for 60 hours.
Has anyone seen an issue like this before? A neighbor had a plane that would randomly drop a cylinder but only when hot and it turned out to be a bad fuel flow divider. I'm typically resistant to throwing new parts and a prayer at a problem....but this one has led me on quite the merry chase. I'm a heartbeat from replacing the entire fuel system. I want to fly my beautiful new plane without this annoying issue.
Any words of experience from the VAF masses?
Signed Desperate in Denver