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sirlegin 12-14-2011 02:46 PM

Rough engine at 1500-1700 rpms
This is an injected Lycoming OF-320. Catto 3 blade fixed pitch. 10 hours
The engine starts and idles nicely, however both on the ground and in the air when the throttle is advanced to 1500rpm the engine becomes rough and does not respond well to the throttle until 1800 rpms are reached and then the engine will play catch up and go to 2000 rpms.
While at 4500 ft and after about 35 minutes of flight I could get no rpm's above idle. I switched tanks from left to right with the boost pump on and after a little while, varying throttle settings, the rpm's came back. I had switched the tanks after 30 minutes from right to left about 5 minutes earlier. I think this was more coincidental rather than significant. When I did have rpm's I was also getting backfires. There was no holding a set rpm and surges of 1 to 300 rpm on any setting above 1200 rpm was the norm. There was alot of throttle movement with no reaction from the engine.
The engine never made full power and at best WOT at cruise was 2500 rpm.
I ran it up back at the hangar and the same dead zone at 1500 to 1700 rpm was evident but none of the other inflight symptoms.
I have changed the injectors, sealed induction leaks, cleaned fuel filters and have run out of idea's.
Below is a graph of the MAP vs engine rpm's and there is a definate lack at the dead zone area. 1500-1700 rpm's.
I have a K&N filter which was recently cleaned and re oiled, perhaps too much oil?
Any thoughts would be greatly appreciated.


dlloyd3 12-14-2011 03:00 PM

Rough engine
My engine on 1st start did not respond well to throttle, was rough at and above idle to near full throttle and backfired. Idle mixture was too lean. Simple to adjust.

sirlegin 12-14-2011 05:07 PM

The engine is only rough running at 1500-1700 rpm. It starts and idles nicely.

Bruce 12-14-2011 05:21 PM


First thing----DO NOT FLY till you figure out your fuel flow problem.
You are asking for trouble.
There are plenty of guys out there that can help you.
I would change the filter to paper if you can. Don't know how much oil
you used but don't think that is the problem.

Pull off fuel line to engine and do a fuel flow test.
Check the mixture lever and make sure it is hitting the stops.
Do you run it full rich?? or are you leaning??
What is your egt's showing 1200-1300??

Give Walt a call if this doesn't help.

sirlegin 12-14-2011 05:36 PM

Definately not flying until the problem is resolved.
During the flight when things started going horribly wrong, average CHT was 357, EGT 1412. After flight before shut down:
CHT's 1)330 EGT 1377
2)282 1374
3)342 1223
4)308 1423
The fuel burn for the hour was 5.5 gph so possibly quite lean or fuel starvation?
This is a FADEC run engine so no mixture adjustments available by pilot.
I will be calling on Walt who helped me with pre certification checks etc, (Thanked on the mothership 1st flight note) although he is not familiar with FADEC systems.

Bruce 12-14-2011 05:46 PM


Walt is your man.

It does look like it is running lean. I would do that
fuel flow test and go from there.

Glad your not getting air under the wings.
You had me scared for a second.


sirlegin 12-14-2011 06:18 PM

Will do Bruce and thanks.
However, how would the fuel flow affect the MAP graph with the loss of non ambient pressure at 1500+ rpm per the chart?

Ron Lee 12-14-2011 08:37 PM

With a FADEC you have other things that may go wrong. Since you can duplicate the problem on the ground, I suggest just one change at a time then see if it works properly.

Steve 12-15-2011 06:05 PM

leaks at the fittings
My friend has an injected O-320 in his 9A. He had low fuel pressure and much air the lines due to loose fuel line fittings at the tanks. He tightened every fitting in the fuel systems and all was well for the last 2 years. However it seems the problem may be returning as he felt a bit of roughness on a recent flight. I mentioned he should closely inspect all the flares on the fuel lines. Perhaps replace the lines with the Bonaco braided product.

Walt 12-15-2011 07:28 PM

I'll have to get up to speed on the Aerosance FADEC system as yours is the first one I've encountered. If you have the manual in PDF send me a copy and I'll have a look at it, then we'll go from there.

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