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The Unknown Filter

The Unknown Filter

To get the full story, read this article first.

The engine finally started but was obviously starved for fuel. It wouldn't run much past idle and struggled to do that. I decided against the fuel filter being the culprit. If the engine was running before it was unlikely the filter would be clogged enough. It was then I remembered a little known filter within the pump itself. In reality it is more like a strainer with a very fine mesh. And it's small. Very small.

The internal filter is accessed via this cap on the bottom on the pump. Twist the cap. You may have to use a wrench on the bottom.

Why is this strainer in the pump?

The pump needs protection too

Upon removing the cap (and catching most of the diesel in a plastic bag) the culprit was obvious. A collection of debris completely covered the filter. It had apparently never been checked. We cleaned it as carefully as possible (considering the circumstances) but still managed to damage the mesh a little. This was not part of our spares and there certainly wasn't one aboard, so we were forced to reinstall the damaged filter. We assumed the downstream filter cartridge would catch any debris before it reached the injector pump. We could only hope any remaining debris in the tank wouldn't damage the pump the mesh filter was designed to protect.

The mesh is so fine it is easily damaged, so be careful!

Finally, safely at anchor 

After reassembling the pump, we had to bleed the fuel injection system. Luckily, like most of the Universal engines used by Catalina, this engine had a self bleed return valve so it was relatively easy to bleed. Once that task was accomplished, the engine started and ran fine. We were able to make our way into the anchorage while we could still see the coral, drop anchor and have another round of rum punch.


A close up shot showing the delicate fine mesh filter

Remember to check all of your fuel filters

Primary, secondary, and pump filters!

In any case, this illustrates the need for periodic cleaning of the pump filter. On most occasions, when you check the filter it will be just fine. But occasionally you may find debris that will compromise the safety of your boat. The appropriate time to check the fuel pump filter is at the time you replace the fuel filter cartridge. You will have introduced air into the fuel system and need to bleed it anyway. Why not clean the fuel pump filter at the same time?

Although the M-25XPB and M-35B engines were supplied with their own rectangular electric fuel pumps, a few owners report having this remote cylindrical fuel pump as well. Double check your installation to see if a cylidrical fuel pump is present.

For the complete engine maintenance story, start with the first article: Periodic Engine Maintenance and Spares.

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