Volvo md6a

[Scary_Des]

Help!! I have a problem with my engine. Out of gear it will rev. to 1700+rpm. In gear it will only rev. to 950 rpm. At this speed it does not miss or splutter but the engine sounds like it is labouring.
I have checked the prop, prop shaft and gear box. I have changed the gear box oil (that was fun) and all seem OK. I can turn the gear box/ prop shaft both ways by hand when it's out of gear. The gear box makes no funny noises. I have checked the air inlet and fuel system as far as I can. Now I'm stumped can anyone help?

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[Talbot]

try a clean filter,, it may be that insufficient fuel is able to get to the engine to enable it to run under load. (I assume you have already ensured that the fuel system has been bled to remove any air locks).

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[Scary_Des]

Good point, filters are Jan 03 but that doesn't stop them being blocked. Tell me with a blocked filter doesn't the engine splutter and miss?

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[Mudhook]

A very similar problem on my MD7 turned out to be barnacles on the prop. You say you have checked your prop, but I had to get close with snorkel and goggles to see this stuff. Only in the river (Orwell) for three months and I had little shells all over the prop. Scraped off quite easily with smooth side of old hacksaw blade, and restored my 2 knots to 5 knots under engine. I wouldn't have believed it until I checked it. A good clue is that, with the negine ahead and your boat securely tied up, the prop wash should run out pretty straight behind. If it seems to go out in a wide V-shape then the prop is very likely fouled in this way - there's little lift and lots of drag!

Regards, Mudhook.

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[dickh]

Also check the Exhaust Elbow is not blocked with carbon & deposits. This will mean removing from the boat and checking - if you only find a small hole(say ½" dia), then this is your problem - clean out or renew.
This is quite a common - I've had it on my boat and my friends boat this year.

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I'd rather be sailing... /forums/images/icons/smile.gif

 

[Scary_Des]

Thanks Mudhook I,ll take a closer look.

Dickh is this a gradual thing or can it happen quickly? The boat has not been used for a couple of months but before that it was OK.

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[Guest]

dick has the right idea, a diesel engine needs certain things to run properly, good compression and air and fuel (in the right place!) and somewhere for the resulting product to go.
if the system needs bleeding the engine wont run properly and certainly wouldnt rev to 1900 unloaded so forget about that, lack of fuel causes the engine to sound as if it is not under load as it dies.
if the engine labours and wont rev, it either has a mechanical drag on it or something is stopping the ingress of air or the egress of exhaust products.
you seem to have checked everything except the exhaust system, it sounds as if it may be getting blocked, salt and carbon at the injection elbow?


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[Scary_Des]

Thank GCW I'll nip down and pull it off over the W/E. I will let you know what I
find.

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[KMM]

Had similar problem with same model engine some time ago. Do to age of installation, problem proved to be rubber exhaust hose delaminating internally, causing cross section to be a fraction of what it should be, thereby restricting flow.

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