Engine Misfiring on Throttle Back

[Mark Castle-Smith]

Hi

I wonder if there is anyone out there who can help me with my engine problem. I have a Lycoming IO-360 200hp with FADEC connected to the VM1000 engine display. I have a 3 blade MT constant speed prop. I went up for my first RV test flight yesterday after four years of building- great feeling! However, after 40 minutes at 25inches square with the engine feeling very smooth and, we throttled back to land and the engine started to hunt (as if the prop was cycling) and misfire and ran very roughly, on slow throttle increase the engine went back to running fine until I throttled back and the symptoms started again, less hunting but badly misfiring Anyway, as we always stayed within gliding range of the airfied we landed safely and would be very grateful for any ideas. Regards from the UK.

 

[Jamie]

Congrats Mark! It's really fun, huh?

I would start by checking your injectors. Remove them one at a time and blow them out. I'm not an engine gear head, but it would seem to me that if the line is partially blocked it would cause a lean condition on that cylinder, which will shut it down when you throttle back.

I'm not too familiar with the VM1000 engine monitor, but if it has data logging capability I would download it to a PC and chart the CHTs and EGTs. You may find a hint of a partially blocked injector line by looking for one cylinder with a noticeably higher EGT than the others.

If your problem is simply a popping sound when you throttle back -- well, it just means that you have an RV with FI and a Vetterman exhaust. I have found being a little more conservative when throttling back will avoid the popping sound.

Again, I'm no engine guy but these are my amateurish observations.

Congrats again! Enjoy that airplane!

 

[frankh]

Popping

I use it to wake up the neighbours....I had on guy tell me thought I was "going down"...it is loud an obnoxious though so gently throttling helps a lot.

Frank

 

[Tandem46]

Mark,

Misfiring or backfiring? My IO-360 has always backfired if I pull the throttle to idle too quickly from a higher throttle setting. I was told its "normal" and what's happening is that the prop is driving the engine (vice the other way around) and the popping you're hearing is unburnt fuel in the exhaust igniting. I've learned to gradually pull the throttle back and gradually slow down which eliminates the backfiring.

 

[Rene Bubberman]

Sounds familiar...

Hi Mark,

Congrats on your first flight! Hop over to Lelystad EHLE if you are ready for it!
A little backfiring is normal, see the other comments, but misfiring / rough running is something else. We have had similar problems. We had the Fadec hooked up to a laptop via the SBC so from the recorded data Jabe at Aerosance concluded that our #4 cylinder misbehaved. You can see it by a rise (partially blocked) or drop (cylinder offline) in the EHT. We cleaned the lines and the #4 injector but the problem came back after two hours. We then exchanged the #4 injector with a new one (225 dollar!) and cleaned the Spark plugs because Mahlon suggested that they could have been fouled by the rough running. We have flown about three hours since without problems and the engine is even smoother then before. Some more info on our adventures: http://websites.expercraft.com/PHVII/index.php?q=log_entry&log_id=20157 and beyond.
This kind of trouble seems to be quite normal and Fadec engines always have it with their #2 and #4 cylinders. Even Mahlon does not know why!
Do not hesitate to mail if you want to exchange more info.

 

[pboyce]

Mark:

After 350 hours on my RV-7A, I had a rough running engine problem. Which exhibited itself only in flight, not taxiing or run-up.

Jabe Luttrell at Aerosance was extremely helpful in diagnosing the problem. He really knows his stuff! Turns out that one or more of the injectors got a bit of dirt in them, leading to erratic functioning.

I replaced all the injectors and the problem is now solved.

I also added a 5 micron fuel filter to prevent future problems. This is a high-performance high-volume automotive filter with a paper cartridge. Made by Mallory model 3160, about $80. My plan is to replace the $20 cartridge every year. I DO NOT want this to happen again!

I went with an automotive filter because from what I can tell, there is no aviation filter available with 5 micron filtration.

The FADEC injectors are precision pieces of equipment, apparently sensitive to dirt. It behooves us to keep them scrupulously clean.

FYI: these injectors cannot be cleaned by 'blowing them out'. They are more like sophisticated auto injectors, rather than traditional aviation injectors.

Paul