Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 28-07-2018, 19:05   #1
Registered User

Join Date: Nov 2014
Posts: 37
Yanmar low RPM under load

I have a Yanmar 3QM30H and recently while in gear it will only go up to 1900 RPM. It also kicks out extra black unburnt fuel from the exhaust. While in neutral the motor RPM goes up to it normal level.
I have pulled off the mixing elbow (2 years old) and it still is in good shape. I removed the injectors and had them professional cleaned. I visibly inspected the exhaust manifold, while still attached to the motor. I could not see anything that stood out. Also while under load, I manually disengaged the compression from each cylinder. There was no change in motor sound on the middle cylinder. The other 2 you could hear the change in the motor.
So that brings me to the next question. What is it. The only thing else I thing I could do is to remove the exhaust manifold and inspected it better. Other than than, is the middle cylinder done. Any assistance would be appreciated.
__________________

jmurray109 is offline   Reply With Quote
Old 28-07-2018, 19:21   #2
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 8,763
Re: Yanmar low RPM under load

Quote:
Originally Posted by jmurray109 View Post
I have a Yanmar 3QM30H and recently while in gear it will only go up to 1900 RPM. It also kicks out extra black unburnt fuel from the exhaust. While in neutral the motor RPM goes up to it normal level.
I have pulled off the mixing elbow (2 years old) and it still is in good shape. I removed the injectors and had them professional cleaned. I visibly inspected the exhaust manifold, while still attached to the motor. I could not see anything that stood out. Also while under load, I manually disengaged the compression from each cylinder. There was no change in motor sound on the middle cylinder. The other 2 you could hear the change in the motor.
So that brings me to the next question. What is it. The only thing else I thing I could do is to remove the exhaust manifold and inspected it better. Other than than, is the middle cylinder done. Any assistance would be appreciated.
Check valve lash (tappets) on middle cylinder - actually check all of them.
Does sound like middle cylinder is not good. Valve burnt?
Compression check?

Have you checked that the prop and bottom is clean?
__________________

__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 28-07-2018, 20:26   #3
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 22,255
Re: Yanmar low RPM under load

OK, after you check valve adjustment, just for kicks try loosening each injector line at idle, once they leak, that cylinder should cut, just in case somehow your decompression lever is messed up.
But it certainly sounds as if you have a dead cylinder.

One of the three cylinder Yanmars is bad about breaking pistons, I don't know which one
a64pilot is online now   Reply With Quote
Old 28-07-2018, 20:41   #4
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 8,763
Re: Yanmar low RPM under load

Quote:
Originally Posted by a64pilot View Post
OK, after you check valve adjustment, just for kicks try loosening each injector line at idle, once they leak, that cylinder should cut, just in case somehow your decompression lever is messed up.
But it certainly sounds as if you have a dead cylinder.

One of the three cylinder Yanmars is bad about breaking pistons, I don't know which one
Good tip about the decompression lever!

It was early 3GM30's and IIRC, it was number 3 (furtherest from flywheel). Supposedly had a bad batch of pistons but why it was only number 3 eludes me. Might be wrong of course .
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 28-07-2018, 23:11   #5
Registered User

Join Date: Nov 2014
Posts: 37
Re: Yanmar low RPM under load

Bottom clean and nothing on the prop. I am not a motor head and I am volunteering my time for a youth sailing group. Trying to fix something and I am way over my head. I am hoping it is not the cylinder, and hoping to find a clogged exhaust. Thanks
jmurray109 is offline   Reply With Quote
Old 28-07-2018, 23:34   #6
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 8,763
Re: Yanmar low RPM under load

OK, well first try the easiest, check the tappet clearance (valve lash) on the middle cylinder. It should be about 8 thou (0.008" or 0.2mm). If that is OK, then try A64's idea (post#3). After that, it's a compression test or call a mechanic.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 29-07-2018, 03:34   #7
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 2,049
Images: 7
Re: Yanmar low RPM under load

Heavy black smoke and lack of engine revs is a classic sign of engine overload.
RaymondR is offline   Reply With Quote
Old 29-07-2018, 09:27   #8
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 22,255
Yanmar low RPM under load

Quote:
Originally Posted by RaymondR View Post
Heavy black smoke and lack of engine revs is a classic sign of engine overload.


It is, because itís excess burned fuel, reason is an overloaded engine doesnít pull in as much air but the pump is injecting the right amount of fuel, remember Diesels unlike spark ignition engines donít have a carburetor that meters fuel and air together.
So a dead cylinder will be excess fuel, cause itís not burning it and can show similar symptoms.

Hopefully Itís a too tight valve, and hopefully it hasnít been burnt.
a64pilot is online now   Reply With Quote
Old 29-07-2018, 10:10   #9
Registered User

Join Date: Aug 2017
Location: Missoula, MT
Boat: Flicka 20
Posts: 42
Re: Yanmar low RPM under load

Had a bad air cleaner and it blew black smoke under load. I had inspected it and it looked slightly dirty but not clogged. Boy was I wrong. Replaced it and the engine ran fine. Usually the problem is simple. Just an idea.

CaptainJohn49
CaptainJohn49 is offline   Reply With Quote
Old 29-07-2018, 11:01   #10
Registered User

Join Date: Nov 2009
Boat: Tayana 37 Pilot House
Posts: 36
Re: Yanmar low RPM under load

That's a good approach, starting with the simplest and least complicated first. Factory trained Yanmar mechanics commonly say that if they can't find external causes for low rpm under load (i.e. dirty fuel, dirty fuel filter, dirty air filter, dirty injectors, plugged exhaust) they will then usually find that the head is carboned up because the owner is afraid of over-revving the engine. This particularly applies to those of us who mostly use the motor just to come in and out of a marina or an anchorage.
Taipe is offline   Reply With Quote
Old 29-07-2018, 16:06   #11
Registered User

Join Date: Sep 2007
Location: Queensland, Australia
Boat: None at present--between vessels. Ex Piver Loadstar 12.5 metres
Posts: 748
Re: Yanmar low RPM under load

OK--Stating the obvious--check your propeller for damage or obstruction such as rope etc. If the engine is straining and throwing out black smoke--you run a risk of damaging both engine and gearbox.
Mike Banks is offline   Reply With Quote
Old 29-07-2018, 20:26   #12
Registered User
 
Jerry Woodward's Avatar

Join Date: May 2008
Location: Punta Gorda/Kentucky
Boat: PDQ 32 LRC
Posts: 370
Re: Yanmar low RPM under load

I question how you know the mixing elbow is in good shape? You can't really see up into the elbow and it could very well have a constriction that you can't see. I had similar issues with my 2GM20F engines although not to that extreme. The elbows looked pristine from the outside and I couldn't see any obvious problem, but replaced them anyway. Solved the problem. There is a reason why they call it the achilles elbow.
__________________
s/v Terrapin
May the four winds blow you safely home
Jerry Woodward is offline   Reply With Quote
Old 29-07-2018, 21:44   #13
Registered User

Join Date: Nov 2014
Posts: 37
Re: Yanmar low RPM under load

Quote:
Originally Posted by Jerry Woodward View Post
I question how you know the mixing elbow is in good shape? You can't really see up into the elbow and it could very well have a constriction that you can't see. I had similar issues with my 2GM20F engines although not to that extreme. The elbows looked pristine from the outside and I couldn't see any obvious problem, but replaced them anyway. Solved the problem. There is a reason why they call it the achilles elbow.


I removed the elbow, not sure if you would even call it an elbow because it is almost straight. This engine has 2 types of mixing elbows one that is almost 180 and one that has a slight bend. I could see everything and it was clean. I had replaced this elbow approximately 2 years ago, and it was still in good shape.
jmurray109 is offline   Reply With Quote
Old 29-07-2018, 21:46   #14
Registered User

Join Date: Nov 2014
Posts: 37
Re: Yanmar low RPM under load

Quote:
Originally Posted by CaptainJohn49 View Post
Had a bad air cleaner and it blew black smoke under load. I had inspected it and it looked slightly dirty but not clogged. Boy was I wrong. Replaced it and the engine ran fine. Usually the problem is simple. Just an idea.

CaptainJohn49


Took the air cleaner off and ran engine without. Still same issue.
jmurray109 is offline   Reply With Quote
Old 30-07-2018, 12:35   #15
ATC
Marine Service Provider

Join Date: Feb 2011
Location: St Petersburg, FL
Boat: 18' Banno USA Old World
Posts: 76
Re: Yanmar low RPM under load

Wow, the second time today, your exhaust mixing elbow is 'caking up' with carbon. This causes restriction in the exhaust and you have unburnt fuel, a reduction in RPM's and horsepower.
__________________

__________________
Absolute,

"Suckin Sludge & Havin a Gas"
ATC is offline   Reply With Quote
Reply

Tags
loa, rpm, yanmar

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
PERKINS 4108 LOW RPM UNDER LOAD...help! avazquez Engines and Propulsion Systems 47 10-06-2016 13:02
Yanmar 2gm white smoke low rpm Captryan23 Engines and Propulsion Systems 8 25-01-2016 12:09
3HM35 Yanmar stalls under load. What next? Canibul Engines and Propulsion Systems 16 05-03-2014 11:46
Yanmar excessive no load rpm? Capt.Alex Engines and Propulsion Systems 11 05-03-2013 06:26
Fouled Injectors > Low RPM & Smoke? Northeaster Engines and Propulsion Systems 30 11-05-2009 15:26



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:05.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.