Question: I have a 1989 Sea Ray with 375-hp Caterpillar 3208 diesels. Last year I overheated one of them and blew a head gasket. Overheating had been a problem for some time prior, incidentally. Anyway, I determined shortly thereafter that the gasket had blown into the cylinder although no cooling fluid had escaped. So I hired a diesel shop to make repairs but now, though both mains run up to 2200 rpm, the one that was recently repaired simply stops there while the other goes up to 2800 rpm. I’ve checked the problematic engine’s timing, turbo boost, injectors, and injector pump. There is no excessive smoke, no excessive blow-by, and no intake or exhaust blockage. Moreover, I’ve done an impeller change, consulted with lots of mechanics, but still the problem remains. What’s going on?
Professor Diesel: First, make sure the throttle at the fuel-injection pump is going all the way from idle stop to full-throttle stop. Falling short by as little as an eighth of an inch can cause the problem you’re having. Second, make sure the transmission and prop shaft are turning freely. Try shifting the engine into neutral while underway—if the shaft spins smoothly you’ve eliminated a drive-train issue. And third, try running the engine off a separate fuel supply, like an adjoining tank. Should the problem persist, you know it is not fuel-related.
Now for some specifics. Lift-pump pressure at the fuel injection pump may be low resulting in a power reduction. Fuel filters can be dirty; change the elements, including the one in the small filter unit that may be on the inlet side of the lift pump. Hoses and clamps associated with the boost compensator on the fuel injection pump may also be leaking, a problem that’s easy to spot when the engine is running. Finally, there may be a restriction on turbo boost (or some part of the exhaust system) or the engine’s valves may simply need adjusting. You’ll find the proper clearance values in your engine manual.
Professor Diesel is Larry Berlin, director of Mack Boring’s Training Services division.
This article originally appeared in the January 2011 issue of Power & Motoryacht magazine.