Engine won't make RPM's II

[thunderhoof]

Since the first time I started this thread about my Volvo Penta MD2030 (2003, 2000 hrs) I have replaced my flexible fuel lines (the real problem), all filters, rebuilt the injectors, and bled the system several times. It now starts instantly and runs smoother than ever... up to a point. The throttle response seems about normal up to about 2600 rpm - half throttle underway. Boat speed is correct for that setting. If I push past that point the rpms will not increase toward the normal 3200 rpm I used for 10 years. I also see and smell some black smoke from the exhaust. If I back down below 2600 rpm the engine acts as if it is happy and will run all day with no symptoms.
Any ideas? Is it time to rebuild the high pressure pump?
I have bled the injectors at 2000 rpm. Should I do it at 3000 which I can reach at no load?
Thanks

[DougR]

At first glance it sounds like the engine is overloaded/ over propped, so the first thing is to make sure the bottom and the propeller are clean.

The fact that the engine cannot rev beyond 2600 could be a lack of fuel issue, but the black smoke indicates that there is plenty of fuel, but maybe not enough air to burn that fuel, so:
- Check the air filter for restriction, or try running without it.
- Check the exhaust elbow and exhaust manifold or exhaust hose for carbon build up / restriction. If the engine can't get rid of exhaust freely, it won't be able to pull in clean air to burn the fuel that is being injected....resulting in loss of power & black smoke.

Once the injectors are bled, they are bled, so no worries there.

DougR

[Badsanta]

Agree with Doug. Check prop. Maybe just fowled growth or picked up an discarded line

[Lepke]

Another check is air volume coming to the engine. As other said, black smoke is too much fuel for the air. Besides the intake, many people, trying to quiet their engine, restrict their engine room vents. An easy test, when running at near wot, open the engine room door, hatch, etc. If black smoke goes and rpms raise then you know.

[Captjohn4]

I had a similar situation with a volvo 2040D 2 years ago. I had pulled into Atlantic Yacht Basin in Va and complained of the boat not going past 4.5 kts. My first suggestion was to check the compression. Their response was everything is fine with the engine what was wrong was the pitch of the prop - they hauled the boat and shipped off the prop to PYI in CA for adjustment. The folks at PYI changed the pitch but returned to me the original pitch key. They put the prop back on and the same thing. Their next solution was to have the injectors cleaned. Still no joy - finally they did a compression test and found the middle cylindar was off. Pulled the head and found a cracked valve spring. Sent off the head to volvo and had ir completely rebuilt and now all is good. CHECK THE COMPRESSION.

[stormalong]

Check the exhaust for blockage - especially the water injector elbow. I had a friend with the same problem - even overhauled the engine with no relief. Then found the carbon buildup. Once cleared all was well.

[Thumbs Up]

clogged exhaust elbow

[Cheechako]

How many rpms can you get in neutral? If a lot higher than it is a prop or dirty bottom issue etc.

[seabreez]

Originally Posted by thunderhoof

Since the first time I started this thread about my Volvo Penta MD2030 (2003, 2000 hrs) I have replaced my flexible fuel lines (the real problem), all filters, rebuilt the injectors, and bled the system several times. It now starts instantly and runs smoother than ever... up to a point. The throttle response seems about normal up to about 2600 rpm - half throttle underway. Boat speed is correct for that setting. If I push past that point the rpms will not increase toward the normal 3200 rpm I used for 10 years. I also see and smell some black smoke from the exhaust. If I back down below 2600 rpm the engine acts as if it is happy and will run all day with no symptoms.
Any ideas? Is it time to rebuild the high pressure pump?
I have bled the injectors at 2000 rpm. Should I do it at 3000 which I can reach at no load?
Thanks

A quick little test is crack open the fuel line going to an injector, do one at a time and check how the engine reacts, try all cylinders and compare the engine miss. If one cylinder reacts differently I would do a compression test for further investigation...

[travellerw]

I throw my bet in with clogged exhaust elbow.

[ballvalve]

yep same problem on my 2040 - blocked exhaust elbow, tried to clear the carbon out and the inside was completely coroded and fell apart, stainless replacement ones costs around the same and will out last the cast one

[thunderhoof]

You guys have good info. The elbow comes off this week.
Thanks,
Dick