[Antoine MTA]

Hello aviators !

I'm looking for your advice as my RV8 has now about 35 hrs and since the beginning I have a problem on cylinder #3.

Here is the configuration of my engine:
- LYCOMING IO-360 Parallel Valve 180hp – Overhauled in authorized workshop
- Dual P-Mag
- Superior Cold Air Sump
- Fuel Injection System AVSTAR AVX360-1 brand new (including flow divider and injectors)
- MT-Propeller 3-blades constant speed
- Idle power is set around 700 RPM. Increase of about 80 RPM while idling test at 1000 tr/min.

I have an issue on cylinder #3 from the beginning that appears in two specific cases (all the time):

- In flight, if I throttle back to idle power, and propeller slow down the aircraft due to constant speed regulation, EGT#3 falls while others are increasing. Engine vibrates and is running rough until I add power or until propeller stops to slow down the aircraft. Feeling would confirm that engine is running only on 3 cylinders.

- On ground, same problem with EGT#3 falling at idle power but with the difference that engine seems to run smoothly on its 4 cylinders. And then EGT#3 becomes hotter than all other EGTs.

Here you can see what records show :

IN FLIGHT :



And ON-GROUND :



What already have been done:
- Cross of EGT probe between cylinder 1 and 3 – No effect, probes are functioning.
- Verification of EGT probe distances from cylinders, all the same and within specs.
- Spark plug test ok, change of both spark plugs on cylinder #3 – no effect.
- Check of spark plug wiring – all good
- Cleaning of pipe from flow divider to injector
- Injector check – all good, and cleaning.
- Flow rate test with injectors #1 and #3 in cups, with boost pump ON at idle power and full power. Cylinder #3 flow rate is slightly but not significantly higher than cylinder #1 at idle power.
- Pressure test of MAP circuit OK (MAP is taken on cylinder #3 to MAP sensor and both P-MAG)
- Spark plugs are quite black but not oil fooled, engine is still a bit too rich I think. I always lean the engine during taxi. However as the engine is still in break-in process, I couldn't climb and run it at lean of peak during cruise.

I had to lean quite a lot the fuel servo with the screw on idle linkage from factory setting.

I’m now running out of ideas to determine origin of this problem; I would appreciate further advice if you have already encountered this problem ?

Antoine - RV8 F-PCMA

 

[Cth6]

One item you may want to try.

Flip the PMAG wires between Cylinder 3&4 to see if the problem follows. If they are long enough swap the plug wires as well. This would rule out a PMAG issue. If it moves to Cylinder 4, then start to slowly move back to the original condition until the issue moves back to 3.

PMAGs Fire 1&2 at the same time and 3&4 at the same time.