Engine Vibration and Exhaust Noise at Low Power Settings

Any DA40 related topics

Moderators: Rick, Lance Murray

User avatar
Pawarren
1 Diamond Member
1 Diamond Member
Posts: 3
Joined: Tue Oct 08, 2019 12:09 am
First Name: Patrick
Aircraft Type: DA40
Aircraft Registration: N821T
Airports: KOSU
Has thanked: 2 times

Engine Vibration and Exhaust Noise at Low Power Settings

Post by Pawarren »

Hello, I'm new to the forum.

I'm prepping for a commercial checkride in my 2012 DA40XLS. When performing simulated engine out maneuvers and steep spirals, I'm getting a fairly significant engine vibration and an occasional popping from the exhaust. This happens only with the throttle closed or nearly closed, and adding a few inches of manifold pressure typically eliminates the vibrations. Engine performance is otherwise near perfect with normal cruise and climb performance, fuel consumption, and CHT/EGTs. It is just out of annual with all compressions >70 and no issues other than an exhaust valve seal that needed replacement. Engine tach time is only 400 hours.

I'm going to need to get it into the shop to address this before my checkride, but was wondering if anyone had dealt with this issue or could give me some idea of where to start.

Cheers,
Patrick
User avatar
Rich
5 Diamonds Member
5 Diamonds Member
Posts: 4592
Joined: Mon Aug 30, 2010 12:40 pm
First Name: Rich
Aircraft Type: DA40
Aircraft Registration: N40XE
Airports: S39 Prineville OR
Has thanked: 145 times
Been thanked: 1180 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Rich »

Questions:
MP/Prop/mixture/airspeed in these cases?
At what RPM does your engine idle with throttle pulled all the way back?
Have you had idle mixture checked?
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
User avatar
Colin
5 Diamonds Member
5 Diamonds Member
Posts: 2006
Joined: Sat Aug 21, 2010 8:37 pm
First Name: Colin
Aircraft Type: DA42
Aircraft Registration: N972RD
Airports: KFHR
Has thanked: 319 times
Been thanked: 527 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Colin »

When this happened to me John Deakin said it was an intake manifold leak. Just in case you have your mechanic looking at it and want to point him in a direction.
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
colin@mightycheese.com * send email rather than PM
http://www.flyingsummers.com
N972RD DA42 G1000 2.0 s/n 42.AC100 (sold!)
N971RD DA40 G1000 s/n 40.508 (traded)
User avatar
Pawarren
1 Diamond Member
1 Diamond Member
Posts: 3
Joined: Tue Oct 08, 2019 12:09 am
First Name: Patrick
Aircraft Type: DA40
Aircraft Registration: N821T
Airports: KOSU
Has thanked: 2 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Pawarren »

It usually occurs between 68 and 85KIAS with MP<6, prop full forward, and mixture rich. I think the engine idles at around 940-960rpm, but I'll go out and confirm that tomorrow. Thanks for the input.
User avatar
Rich
5 Diamonds Member
5 Diamonds Member
Posts: 4592
Joined: Mon Aug 30, 2010 12:40 pm
First Name: Rich
Aircraft Type: DA40
Aircraft Registration: N40XE
Airports: S39 Prineville OR
Has thanked: 145 times
Been thanked: 1180 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Rich »

I like the idea of an induction leak.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
User avatar
Karl
4 Diamonds Member
4 Diamonds Member
Posts: 317
Joined: Wed Aug 04, 2010 3:58 am
First Name: Karl
Aircraft Type: DA40
Airports:
Has thanked: 68 times
Been thanked: 102 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Karl »

Replace the intake manifold gaskets would be my first call.
User avatar
caseyayers
2 Diamonds Member
2 Diamonds Member
Posts: 36
Joined: Thu Aug 16, 2018 1:27 am
First Name: Casey
Aircraft Type: DA40
Aircraft Registration: N384DM
Airports: KCRG
Has thanked: 19 times
Been thanked: 10 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by caseyayers »

Sorry to dig this thread back up, but I was wondering if you might have confirmed if this was the issue or not? Shortly after my annual in February I started noticing a similar issue. I figured it might be some sort of vibration in the cockpit at first, but I consistently only notice this grinding/vibrating kind of sound when at idle or near idle on final with mixture and prop full forward. As soon as I get the throttle back north of 10” or 12”, it immediately stops, without any real fade; it’s either “grinding” or not. Wondering if I should get this looked at and if this might be a good place to have my shop start at.
User avatar
perossichi
3 Diamonds Member
3 Diamonds Member
Posts: 188
Joined: Tue Sep 18, 2018 4:05 am
First Name: Peter
Aircraft Type: DA40
Aircraft Registration: N925RH
Airports: KVNY
Has thanked: 31 times
Been thanked: 75 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by perossichi »

check your MP at idle on the ground. Should be around 9" or so. Higher manifold pressure is associated with induction leaks. MP is really a measure of the vacuum created by the suction from the engine as the MP sensor is downstream from the throttle butterfly valve. So low values with throttle closed are signs of a heathy induction system. I've never heard of an MP value less than 6, but I don't have a lot of experience outside my plane.

RPM at idle should be something like 700-800 rpm.

Can you download your engine data? If so, put it up on the savvy aviation engine analysis site. You will get some free analytics. If you want to, you can pay them for a professional analysis.

A partially clogged fuel injection nozzle can cause engine roughness at low values of MP (with mixture rich). This cylinder will not develop full power because it is running too lean. When you open the throttle with mixture rich, then you may get enough fuel flow to smooth this out. If this is true, attempts to run LOP will cause a great deal of roughness.

I think Rich's theory should be the maintained hypothesis until proven otherwise, though.
Sold 2002. Powerflo, Hartzell composite two blade, 530W/430, 345 transponder.
User avatar
Pawarren
1 Diamond Member
1 Diamond Member
Posts: 3
Joined: Tue Oct 08, 2019 12:09 am
First Name: Patrick
Aircraft Type: DA40
Aircraft Registration: N821T
Airports: KOSU
Has thanked: 2 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Pawarren »

Turns out it was low ground idle. My mechanic adjusted the idle speed and mixture and the problem seems to have vanished. Every now and then you get lucky with a cheap fix. Cheers.
User avatar
mhoran
4 Diamonds Member
4 Diamonds Member
Posts: 476
Joined: Fri May 23, 2014 11:56 pm
First Name: Matt
Aircraft Type: DA40
Aircraft Registration: N269RB
Airports: KLDJ
Has thanked: 121 times
Been thanked: 244 times

Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by mhoran »

I'm now having this problem as well. My plane came out of annual about 10 hours ago and the situation has slowly been getting worse. I checked with my mechanic and he verified that mag timing and injectors were fine at annual. I believe the vibration was happening before the annual as well, so it would seem there must be something else at play.

I've been poring over a recent engine analysis I uploaded to Savvy (https://apps.savvyaviation.com/flights/ ... 4f74a702a6) but haven't seen anything jump out. At 1000 RPM the MP is just below 11. Seems that's not far off from 9 mentioned in this thread that would suggest an induction leak.

At full power in cruise, there's some vibration but it's not too noticeable. However, when on approach to landing or when taxiing around the airport, the engine is quite rough. I noticed last weekend that the standby airspeed was bouncing around by about 10 knots and the backup HSI was unreadable. My co-owner and I are generally very good about leaning both in the air and on the ground and our spark plugs were clean last they were checked.

Magnetos are okay during run-up but not great. There's some slight roughness on both. But EGT comes up on both mags for all cylinders. The drop is about 150 RPM on both, a bit more on left. I had the idle mixture adjusted a few weeks ago but that didn't help either.

You'll see in the engine analysis above that cylinder 1 runs a bit hotter than the others. I actually have to push fuel flow up to over 10 GPH at 8000 feet to get the temperature down to 404 degrees. This has been a problem for as long as we've had the plane, so I don't think it's directly related to the roughness problem but perhaps it is.

Any thoughts would be appreciated.
Post Reply