Low Maximum Revs

[Scallywag]

I have a Volvo Penta d2-40 with S130 saildrive.

The maximum revs I can get with the gear engaged is only 1800 revs. Previously it reved above 2500 as a maximum. There is nothing around the prop and the prop moves freely.

Does anyone know what could be the problem?

 

[prv]

Just a wild guess, but partial blockage in the fuel supply?

Pete

 

[skip50]

I had a similar problem with a VP 2003.

To cut a long story short, replaced the diesel lift pump, a new sealed pump was available. Problem solved.

On inspection of old pump, a spring on one of the valves was displaced so that the valve was not operating correctly. Indeed, I was surprised the pump operated at all!

Just saying what worked for me.

 

[theoldsalt]

If the engine revs OK out of gear then two things to check. The supply of air and diesel.

I believe if it is lack of air then the exhaust will be very sooty.

If lack of fuel then the lift pump (if one is fitted) may not be delivering the demands of the injector pump. I had this problem on my engine and replaced the mechanical lift pump with an electric one.

 

[scottie]

Blocked exhaust is a likely reason on this engine worth a search on forum

Any smoke?

 

[Tranona]

I have a Volvo Penta d2-40 with S130 saildrive.

The maximum revs I can get with the gear engaged is only 1800 revs. Previously it reved above 2500 as a maximum. There is nothing around the prop and the prop moves freely.

Does anyone know what could be the problem?

It should reach at least 3000 and something like 7.5 knots. You do not say what speed you are, or were getting. Progressive loss of power is either a fueling problem or a choked exhaust. If the 2500 was the maximum you ever had when the engine was new, it suggests the prop is too big, probably too coarse pitch. The overloading of the engine could be the cause of a choked exhaust.

 

[Mistroma]

Blocked exhaust is a likely reason on this engine worth a search on forum

Any smoke?

I'd include this as a possibility as well it happened to me once but was even more extreme. The engine revved in neutral but revs were very limited in gear and then the engine stopped. It could re-start but same thing happened.

I traced the fault to delamination of the flexible hose in the exhaust. Both ends were fine but I found a flap part way down the inside. Exhaust gas caused it to peel away from the sidewall and block the tube. I think that I reversed the tubing as a quick fix to get home so that the gas pushed the flap open and everything was fine.

 

[nigelmercier]

I went through this loop, after a plastic bag on the propeller seemed to limit revs at WOT.
I checked: air supply, fuel supply, exhaust hose and elbow (punching a hole in the latter as I did so). The culprit was the propeller I had fitted; it was the wrong pitch.

 

[Scallywag]

Thanks to all of you for helping so far.

Today I have changed both the main fuel filter and the pre-filter. And removed and cleaned the exhaust elbow (which was a little dirty but not too bad. Removed and checked air filter which seemed fine. Throttle linkage is fine.

The problem persists - seems fine to 1800 revs and then no more revs.

The exhaust seems normal and not sooty.

In answer to Tranona I was getting up to 3000 revs and 7.5kn of boat speed, now 5.5kn.

So, from the answers, I guess I am left with a problem in the flexible exhaust hose (it is ok at the engine end but I have not checked elsewhere) or the fuel pump. Any other ideas?

Is there a way to test the fuel pump apart from swapping it out?

I should add that the engine has done 800hrs since new in 2006 and that the prop is the original fitted by Bavaria.

 

[nigelmercier]

The rubber exhaust hose could be delaminating, or possibly blocked. I pulled a rolled up rag through mine to check for obstructions.

Also, check for air leaks on the fuel suction side.

 

[Tranona]

Thanks to all of you for helping so far.

Today I have changed both the main fuel filter and the pre-filter. And removed and cleaned the exhaust elbow (which was a little dirty but not too bad. Removed and checked air filter which seemed fine. Throttle linkage is fine.

The problem persists - seems fine to 1800 revs and then no more revs.

The exhaust seems normal and not sooty.

In answer to Tranona I was getting up to 3000 revs and 7.5kn of boat speed, now 5.5kn.

So, from the answers, I guess I am left with a problem in the flexible exhaust hose (it is ok at the engine end but I have not checked elsewhere) or the fuel pump. Any other ideas?

Is there a way to test the fuel pump apart from swapping it out?

I should add that the engine has done 800hrs since new in 2006 and that the prop is the original fitted by Bavaria.

Sounds like you may have lost one cylinder if fuel flow is OK. Have you checked by cracking open a fuel pipe at each cylinder when running under load tied up in a berth?. If there is no fuel coming out or the engine revs don't change that cylinder is not working. Could be an injector problem or lack of compression.

The fact that you achieved full revs/speed in the past suggests prop is OK. Fouled prop holding down revs would result in rough running and lots of smoke, so think the problem is with the engine rather than transmission.