RPM Wandering

[dolfuns2]

I have a 1969 38C with original Cummins 555's. Just recently have developed an RPM flux in the port engine, not too noticeable at high RPM, but at low RPM it is enough to stall out the engine. Am hoping it's not the fuel pump, and perhaps just a restriction in the fuel supply or something related. Any advice or experience with similar problem appreciated. I am traveling right now, and have not been able to trouble shoot at all, but plan to attack the problem when I return next week. Tks, Billy

[Genesis]

... on any diesel is almost always either fuel supply or governor related, and are usually the first.

The fuel supply side is the easy one to check. Do you have vacuum gauges on your supply side past the primary filter(s) but before the lift pump? If not, put some on there and see what kind of vacuum you're pulling.

Also, while you're at it, install a piece of clear fuel line temporarily on the suction side and see if you have air bubbles in the line. Air leaks will also lead to this kind of thing.

[dolfuns2]

Thk for the tips, will try this out when I return home this weekend. Since I'm fairly new to the diesel world, will have to find some sort of engine diagram to identify the lifting pumps/lines, etc, or perhaps I'll be able to figure it out. Again, thanks for the post. Billy

[dolfuns2]

Genisis, I took your advice, and everything looked fine until I discovered a rust spot on the engine mounted fuel filter. As it turns out, the steel had rusted all the way through, and the engine was sucking air in through that spot. Replaced the filter, ran for a few minutes and the problem is solved. Now I have to stop the salt water leak from the manifold that was leaking onto the filter, ie: causing the rust. Thanks again for the help, I' m back to fishing!!! Billy