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25-05-2017, 11:21
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#1
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Registered User
Join Date: Jan 2016
Location: San Diego, CA
Boat: Beneteau 40.7
Posts: 343
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Diesel Won't Make Normal RPMs
The Perkins (Volvo Penta MD2030) on my sailboat suddenly refused to respond to the throttle to turn over 2100 rpm. The max rpm is listed as 3600 and I commonly use it at 2800 to 3200. The engine seems OK to that point with a steady idle at 800 rpm and smooth running up to 2100. When I try to advance the throttle past that the engine seems rough with some black smoke (not dense) from the exhaust. Behavior is the same in neutral and under way.
I have replaced the two fuel filters. There was no evidence of contamination or clogging and the drained fuel is clean with no water. I bled the fuel lines up to the injectors twice with no change in behavior. The three cylinders act the same while I am bleeding them. All drop about the same number of rpms and spray the same amount of fuel when I open the lines.
The engine is 2003 vintage with about 1200 hours on it.
Any ideas? My next step will be to remove the injectors and have them inspected / maintained / replaced.
After that I guess I have to have the injection pump tested. Is there any test I could perform on it while it is mounted to the engine?
Thanks in advance for any help you can supply.
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25-05-2017, 11:29
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#2
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Registered User
Join Date: Dec 2015
Location: Nanaimo BC
Boat: modified Spray 56' oa
Posts: 378
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Re: Diesel Won't Make Normal RPMs
Air filter collapse breath in Exhaust mixer carboned up breath out .Black smoke says air/fuel not tickety boo. (sound of smooth running engine)
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25-05-2017, 11:34
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#3
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Registered User
Join Date: Jan 2017
Location: Mobile
Posts: 9
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Re: Diesel Won't Make Normal RPMs
Your troubleshooting seems focused only on the fuel side. As topmast mentioned, you need to check the air intake and exhaust for restrictions.
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25-05-2017, 11:39
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#4
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Moderator Emeritus
Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,406
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Re: Diesel Won't Make Normal RPMs
Something a little outside the box, did you check to see if your propeller is fouled and that your propeller shaft turns freely?
__________________
David
Life begins where land ends.
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25-05-2017, 13:45
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#5
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Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
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Re: Diesel Won't Make Normal RPMs
Quote:
Originally Posted by David M
Something a little outside the box, did you check to see if your propeller is fouled and that your propeller shaft turns freely?
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OP says it happens in neutral too.
Since he's checked the fuel, I concur with the others who say to look at intake air and exhaust systems.
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25-05-2017, 13:57
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#6
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Registered User
Join Date: Feb 2013
Location: Oregon
Boat: Seafarer36c
Posts: 5,563
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Re: Diesel Won't Make Normal RPMs
He did say in neutral and in gear, so that would rule out an air supply problem because it would still rev higher in neutral. It has to be the other end, because an exhaust blockage wouldn't care about a load just quanity and that would be an rpm limit.
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25-05-2017, 14:02
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#7
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cruiser
Join Date: Jan 2012
Location: Pangaea
Posts: 10,856
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Re: Diesel Won't Make Normal RPMs
Turbo or non turbo? If turbo, have you cleaned out the turbo lately?
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25-05-2017, 14:52
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#8
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,750
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Re: Diesel Won't Make Normal RPMs
I had the same problem with my Yanmar 4JH3 HTE.
I THOUGHT I had checked for fuel issues, and went on to send out the injectors, have a pro look at the turbo, and even send out the injection pump to be bench tested.
Turns out I missed the fine filter. Didn't really even think about it because I had never had any bad fuel problems, and my Racors were always clean. But somehow the fine filter on the engine was very slightly clogged. Didn't show up on the vacuum gauge because that's on the wrong side for that -- it only shows if the Racors are clogged. Once I changed the fine filter, the problem disappeared completely.
My money would be on fuel. Some restriction somewhere, or an air leak. I would eliminate an exhaust restriction (coked up exhaust elbow or water lift muffler maybe) and some restriction in the intake, and then I would go at the fuel system with a fine toothed comb.
One good technique is to make yourself a gravity day tank and hook that up directly to the lift pump -- that will eliminate everything from the lift pump to the tank.
Only after being absolutely sure about no restriction of fuel flow, no problem with the lift pump, no restriction in intake or exhaust, would I start to throw money at injectors or injector pump. This is very unlikely to be the problem, especially since you've already verified that all cylinders are firing equally.
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25-05-2017, 17:03
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#9
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Re: Diesel Won't Make Normal RPMs
If it does it in neutral under no load, I do not think it is air or fuel, cause very little of either is necessary to turn full RPM under no load. I'm betting clogged elbow.
No load pretty much rules out turbo too in my book. But I've been wrong many times
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25-05-2017, 17:22
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#10
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Registered User
Join Date: Jan 2016
Location: San Diego, CA
Boat: Beneteau 40.7
Posts: 343
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Re: Diesel Won't Make Normal RPMs
Thanks for the inputs.
I replaced both the water separator / filter and the engine filter and checked for a strainer in the line (none).
The simple foam air filter fell off recently. The light foam is clamped to the intake runner and it ripped off due to its own weight and engine vibration. Really weak construction. I found almost all of the very light foam in the bilge. I don't think that's it but I will put a borescope into the manifold and take a look. On the exhaust side, water and gas flow seems normal but I I will look at the mixing elbow.
I believe the change in performance was sudden so I like the idea of a sudden restriction rather that simple degradation over time but have not yet found a smoking gun.
Has anyone repaired / replaced the injector pump on this type engine? What were the symptoms before you did and what was the problem with the pump?
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25-05-2017, 20:26
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#11
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,242
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Re: Diesel Won't Make Normal RPMs
Quote:
Originally Posted by a64pilot
If it does it in neutral under no load, I do not think it is air or fuel, cause very little of either is necessary to turn full RPM under no load. I'm betting clogged elbow.
No load pretty much rules out turbo too in my book. But I've been wrong many times
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I with you on this one .
The sudden onset of the problem would normally preclude a clogged elbow but clogged elbows are funny things; often work OK without symptoms and then suddenly they stop the engine .
__________________
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
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25-05-2017, 23:11
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#12
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,750
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Re: Diesel Won't Make Normal RPMs
Quote:
Originally Posted by a64pilot
If it does it in neutral under no load, I do not think it is air or fuel, cause very little of either is necessary to turn full RPM under no load. I'm betting clogged elbow.
No load pretty much rules out turbo too in my book. But I've been wrong many times
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Logical, yet I've seen that very thing - twice. Other time when I tried to install Maretron fuel flow sensors - the restriction caused the engine to develop full revs even in neutral.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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26-05-2017, 07:53
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#13
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Registered User
Join Date: Feb 2016
Location: So Cal
Boat: Lancer 44 Motor Sailer
Posts: 560
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Re: Diesel Won't Make Normal RPMs
Hi guys, I'm late getting in on this one. Just about anything I would guess at being the problem has already been suggested. My first thought was rope or kelp wrapped on prop blades till I read it happens in neutral also. So apparently we can toss that one out the window. I went to the factory owners manual and looked at what they might have to say about not reaching max RPMs. Listed in order given as follows.
Fouled fuel filter
Air in fuel injection system
Water/contaminants in fuel
Boat abnormally loaded
Fouling on underwater hull/drive/propeller
Limited speed control lever movement
Insufficient air supply
Defective/incorrect propeller
My thoughts lean towards blocked air flow, blocked exhaust. O.P. mentioned foam air filter disintegrating. I wonder if any got through the intake or further. Since it happened suddenly I don't think it would be incorrect prop or some of the other things that happen gradually. I learned long ago not to be certain about anything. If it's not the obvious things that we all encounter as obvious causes then it must be something less common. All he can do is go through the easiest cheapest most likely things first and hope that solves the problem. I found on my particular injection pumps a very fine screen where the fuel line enters the injection pump as a final filter. (CAV)When I went through the pump last fall I found the screen was pretty dirty and replaced it with a new one. I would not recommend pulling injectors and pump until all other options are checked first.
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26-05-2017, 09:01
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#14
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Diesel Won't Make Normal RPMs
Quote:
Originally Posted by Dockhead
Logical, yet I've seen that very thing - twice. Other time when I tried to install Maretron fuel flow sensors - the restriction caused the engine to develop full revs even in neutral.
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Yes but. There is always a but, right?
Anyway he says black smoke, that is usually unburned as in excess fuel, so I'm betting not fuel delivery.
Could be as simple as a slipped throttle cable so that its not getting full throttle
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26-05-2017, 09:10
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#15
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Registered User
Join Date: Nov 2016
Location: Gulf Coast of FL
Boat: Pearson
Posts: 408
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Re: Diesel Won't Make Normal RPMs
On another note check cutlass bearing. Could have picked up some fish/trap line and wound tight inside the bearing. Is your gearbox running hot?
__________________
Ken Z
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