Engine performance problems can be a major headache. One common marine diesel engine problem is low power. Low power may or may not be accompanied by dark smoke, and could be caused by a number of issues. In fact, the issue might not even be the engine.

Here’s some important information for marine diesel troubleshooting.

Low Power With Black Smoke

If your engine is producing low power or low rpm and is emitting black smoke, the vessel may be underpowered or overloaded in its current configuration. Being overloaded has a direct effect on the propellers and also causes the engine to work harder.

It could also be that the engine is not getting enough air because of a collapsed or dirty air cleaner, a leaking or worn-out hose, a poorly ventilated engine room or a dirty afterfilter. Any one or a combination of these things can cause the dark smoke and lower the power.

Low Power Without Black Smoke

When low RPM marine diesel engines are not releasing dark smoke, the engine is most likely not getting enough fuel. A lack of fuel could be caused by several different issues, including clogged fuel lines and filters, a broken return check valve, suction air leaks and more.

Troubleshooting Steps

If your engine is not getting enough fuel, but there is no dark smoke, try these marine diesel troubleshooting checks:

1. Check the fuel solenoid control linkage and the throttle.

2. Check and change the filter.

3. Use a pressure gauge to check for a bad return line check valve or pump lift.

What if the Engine Is Not the Problem?

If you’ve tried all these troubleshooting steps and you’re still experiencing low power, the issue is likely external and does not have to do with the engine.

The main external force that drives the boat is the propellers. It’s important to remember that the propellers actually move the boat — the engine just turns them. So, if your propellers are turning at the same RPM but the boat is going slower, then there is some sort of external added weight or load that is bogging down performance.

If your marine diesel engine experiences low power without emitting black smoke or displaying other signs of engine issues, you are most likely dealing with an external overload issue.