Diagnosing a Cranky Engine

By: Frank Lanier

QuestionI have a 2003 Ebbtide Mystique 2400 with a MerCruiser 350 MAG MPI and a Bravo III drive. There are 450 hours on the engine, which starts up with no issues when cold, but I am having a problem starting it after it runs for a while. When the engine is hot or warm, it cranks but will not start until I pump some gas (in neutral). After I give it a little throttle (before starting), it starts right away. Once it starts, there are no issues (idling is fine, etc.). I know I am not supposed to pump any gas with fuel-injected engines prior to starting, but it’s the only way to get it going.

If it matters, I always add the appropriate amount of fuel stabilizer at each fill-up. I have tried using marine-grade fuel (purchased at a marina), but it did not help. The fuel filter was recently replaced, but it did not resolve the problem. What could be the issue?

AnswerMy first recommendation would be to have the engine checked with a Mercury DDT (Digital Diagnostic Tool) for trouble codes. This engine is very sensitive to its sensors, and even a seemingly innocuous problem (e.g., a small vacuum leak) can produce some unusual symptoms. The DDT will show all stored codes, which should provide a better picture of what’s going on and aid in the trouble¬≠shooting process.

Fuel-injected engines can have this issue as a result of air bubbles in the injector lines expanding when the engine reaches operating temperature and is then shut down. Some airplane engines are notorious for this problem and have a special sequence of startup procedures for use when the engine is hot (sort of like your throttle pumping solution). You could take a look to see if any fuel lines are routed too close to the engine, exposing them to excessive heat.


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