Volvo Penta MD2030 Dropping RPM's

[merrytimer]

So I'm coming up river against a bit of current (1-1.5 knots) the other day in my new to me boat, at about 2400 - 2600 rpm and my engine starts dropping about 200 rpm at random times. It would recover in about 5 seconds and wouldn't happen again for 30 - 60 minutes or would happen more frequently. The motor was running very smoothly otherwise and never quit on the trip which lasted about 4 hours. I don't have a temperature gauge but I wasn't getting an alarm. Using a hand held temp. gauge I was getting up to 210 to 220 on the crankcase. So I reduced the revs a bit & got it to cool down 10 degrees but the problem continued although perhaps less frequently. At times it didn't seem like the engine was responding to increased throttle either. Thanks for any suggestions on what might be happening here!

[sandy stone]

99% chance it's a fuel delivery problem. Check/replace the fuel filters to start off with.

[Compass790]

Originally Posted by sandy stone

99% chance it's a fuel delivery problem. Check/replace the fuel filters to start off with.

+1 for this diagnosis.
Also check all connections for air/fuel leaks

[merrytimer]

Thanks very much for those suggestions. I will follow up on them. KJ

[Charlie]

Same problem with a Yanmar. Placed a bot of clear fuel line and found bubbles in the fuel. Lowered RPM. Filled tank next day problem disappeared and hasn't come back.

[tarian]

Check for diesel bug , but this is a classic fuel starvation issue check your primary filter for gunk , if there is you need to get rid of the fuel and clean your tanks and potentially change filters twice . Happened to us this year exactly as you described, happy hunting

[keithw88]

Had a similar symptom. The issue turned out to be that the air supply to the engine compartment was made of flexible ducting, which would periodically collapse when the engine was put under load, and spring back into shape when the engine was throttled back. Took quite some time to work that one out.

[merrytimer]

Thanks very much for taking the time to reply Tarian. This is very useful especially since you had the same problem. I will follow your advice but I really hope I don't have to clean the dang tank!

[Searles]

Check fuel tank breather is clear and clean ,a classic cause of fuel starvation ,a partially blocked or linked breather .a simple check,often over looked

[MicHughV]

a) have you checked your fuel filters lately....???...if you have a vacuum gauge installed you can tell right away if it's a fuel delivery problem..but a dirty bowl is also a good sign..
b) if the boat is used and fuel has been sitting for a while in a tank, all sorts of stuff can grow in there and give the kind of problems you mentioned...it will be a good time to change all the filters and even give the fuel a scrub...or remove and replace...
c) check the tank vent line for blockage....this can also cause fuel starvation...
d) it's possible there is some air in the fuel lines..some small bubbles of air coming thru' a bad connection.....check all the connections for fuel dripping, moisture,etc..

this may require a process of elimination until you find the problem....I've owned two volvo's in prior boats, and while I can't say they are my favorite engine, they should run trouble free...diesels are relatively simply...they require clean fuel and clean air...and they will run forever...

[ftamburrano]

AIR BUBBLES ENTERING.
I agree with other replies to this post: it's a fuel problem that I experienced in the past. Among the causes, check for bad conycal copper joints in the fuel line. These joints shoud be replaced every time the line is disconnected, but very few do. The conical surface is marked every time the line is closed and tightened, reusing it may cause air leaks. Check the upper part of the line, the one getting out verticalli from the top of the reservoir: that part has an internal negative pressure, and it is possible that it sucks air. Use rubber heavy duty line instead of old copper lines. Another cause is microbial growth in the diesel fuel, plugged filters, bent lines (the internel section from circular becomes elliptical, with a lover sectional area, eventually totally squeezed.
Francesco

[merrytimer]

Thank you all for your replies. It gives me confidence in the diagnosis since almost everyone is saying it's a fuel supply or venting issue. I now have a great list of things to check & remediate if necessary & am hopeful I can get the problem solved!