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Engine unresponsive after idling

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Question: I have a 39-foot Bertram with twin Volvo Penta TAMD74P-A diesel inboards. The starboard engine, if left idling for a couple of minutes—say, while I’m fishing over a wreck—will not rev up afterwards. Instead, it takes 30 to 40 seconds to respond. The fuel filters are new, and the fuel onboard is clean. Do you have any ideas?

— John Steward Destin, Florida

Professor Diesel: With the starboard engine switched off and you in the engine room, have a friend move the throttle lever at the helm to full throttle. The point here is to make sure the throttle lever at the engine touches the high-speed adjusting stop on the fuel-injection pump. Now repeat the process on the port engine, making sure both engine-mounted levers move an equal distance with equal effort. If either does not, check for rusty, kinked, or worn cables.

Next compare the movement of the stop levers on both engines. Sometimes a difference of little more than an eighth of an inch will make an engine lazy. If the starboard lever gets less than full travel, check its injection pump.

And finally, try the following: Start both engines, leave them in neutral, and check the throttle and stop levers as described above. Also, check for adequate fuel pressure (specifications are in your service manual) between the starboard engine’s lift pump and its secondary filter and fuel-injection pump. Also check turbo boost and turbo reaction time. Low pressure or slow spool-up may mean a worn-out turbo or a plugged mixing elbow or exhaust system. I’ve seen mufflers plugged with muskrats, eels, fish, dirt, and other undesirables.

I believe your engines also have intercoolers; they should be removed and cleaned occasionally as they can become clogged with marine growth, scale, and other obstructions. If all these engine-related aspects check out, it is possible that prop shaft alignment or other drive-train issues are your problem, especially if that sluggish starboard engine throttles up quickly in neutral.

Professor Diesel is Larry Berlin, director of Mack Boring’s Training Services division.


This article originally appeared in the December 2011 issue of Power & Motoryacht magazine.