Loss of Power - Inboard Volvo Penta Diesel Engine

[Kiwi@Sea]

We have a 1990 volvo penta inboard diesel engine model?AD31P? in our 20ft fishing boat, problem is boat looses power after 2500rpm, have changed all diesel filters, flushed & dried tank, wondering what is the story with the manual diesel pump? does the cap come of the top to expose another filter? is it worth me going in there? any thoughts or opinions would appreciated. it hasnt always had this problem, only noticed it in the past 3mths TIA

[klem]

You need to determine whether this is because there is extra load being placed on the engine or whether you are not delivering enough fuel/air.

If you try to rev it up in neutral, will it hit maximum governed rpm? Have you checked to make sure that there is no growth on the prop or shaft? Have you run aground recently or hit anything that could cause bent propeller blades? Have you done anything else like add significant weight to the boat or any underwater modifications? This should help to figure out whether extra load is being applied to the engine.

The next place to look would be fuel. You have changed the fuel filters which is good. Do you know that the fuel itself is good? Did you cut open one of the old filters to see what was in it? How old is it? If your fuel is good, there are a few other things that can limit delivery. Is your shutdown properly adjusted and traveling the entire way? Have you readjusted your throttle cable? It is possible for a lift pump to go bad or even an injection pump to cause this problem. If you hook up a fuel pressure gauge between the lift pump and injection pump, that should help you. Your engine also has a "smoke limiter" which monitors boost pressure in the intake and limits fuel output if it is too low. It could even be that there is something wrong with your governor.

The next place to look is air. You will probably be able to see more black smoke than usual if you are having an air issue. Likely problems would be a dirty air filter, a boost leak or a worn out turbo. Boost leaks can be frustrating to find and usually are not realized until a boost gauge is connected. To check your turbo bearings, grab the compressor and see whether the shaft has play. Reduced air in itself won't reduce power that much but it will cause your smoke limiter to reduce fuel output.

This is a laundry list of things to look at. Start with the obvious and see whether you are loading the engine more heavily. Then, if you don't see black smoke and if the engine is running well (no air in fuel), start looking for fuel related problems.

Good luck.

[senormechanico]

Same thing happened to me today with my MD2020, only 2500 rpm in neutral with black smoke. I'll bet it's a crudded up exhaust elbow. I'll find out tomorrow.

[MarcW]

Originally Posted by senormechanico

Same thing happened to me today with my MD2020, only 2500 rpm in neutral with black smoke. I'll bet it's a crudded up exhaust elbow. I'll find out tomorrow.

My Farr has a M2030 it had the same problem crud in the exhaust elbow.

[GordMay]

Exhaust Bends MD2010-2040 and 2000 series:

For owners of the compact range of diesel engines a reminder that if your engine tends to overheat when under load, now is the best time to check the exhaust elbow (bend) for a build up of carbon. When checking for this don't be fooled by the fact you can see right through or can blow through with little effort. A small reduction in flow rate is sufficient to cause overheat condition in the most undesirable of situations. Best way to deal with the problem is to remove the elbow, suspend securely on a suitably bent wire coat hanger. Mix carefully a solution of caustic soda and having kitted yourself with suitable gloves and goggles lower the elbow into the solution for the recommended time and do remember to rinse well after this de-coke. A word of caution safety first must take priority over all other considerations. Final word of caution do not attempt to remove deposits with screwdrivers welding rods and the like as exhaust elbows are a couple of hundred quid and sharp tools tend to punch through the twin wall internal, so making them into scrap.

November 28, 2009 ➥ Volvo Penta News

[irw555]

Originally Posted by Kiwi@Sea

We have a 1990 volvo penta inboard diesel engine model?AD31P? in our 20ft fishing boat, problem is boat looses power after 2500rpm, have changed all diesel filters, flushed & dried tank, wondering what is the story with the manual diesel pump? does the cap come of the top to expose another filter? is it worth me going in there? any thoughts or opinions would appreciated. it hasnt always had this problem, only noticed it in the past 3mths TIA

I have a AQAD40B under the top of the lift pump there is a small filter, mine was full of crap, check it out and see how you go, good luck.

[Chief Engineer]

Any Smoke?

Bottom and Running Gear Clean?

Check operation of throttle. Disconnect and manually advance speed.

For a start.