QSB 5.9 Loss of Power at High RPM

[Mike Salsa]

Hello,

I’ve got twin QSB 5.9’s 425hp from 2013 in my Azimut 50. I’ve just had the heat exchangers, after coolers, and turbos replaced which I don’t think are related to this issue.

I’ve intermittently had a sudden loss of power for some time now and its progressively getting more severe and more often. The first time it happened I was cruising around 2500 RPM and I felt a sudden surge (loss of power). It returned to normal so quickly that I couldn’t even tell which motor did it. It did the same thing many more times over the course of about 30 hours but again, so quickly that I couldn’t tell which motor was doing it. I had a separate issue of loss of boost pressure and replaced the turbo which solved that. Starboard lost power during sea trial and the Cummins tech’s attributed to possible water in the fuel. I’ve since had the tanks cleaned, fuel polished, and tanks shocked with a biocide. The problem continues.

Now in a matter of 30 minutes at cruising speed (2500rpm) the starboard motor losses power. If I pull the throttle back quick enough, the motor will stay running. If I don’t, then it will stall and shut off. It does start back up after. This issue only occurs at high RPM. All my fuel filters are brand new. What part can be failing?

Topic

[Clark Leighs]

I’ve read about this happening elsewhere. Belt dust build up or some other contamination interfering with the sensor reading. Or an outright failure.

If the computer doesn’t know where the crank is it will shut the engine down.

[Mike Salsa]

Thanks for the info Tony. Considering all the work that has been done over the past couple months, I waited for a technician to come out. The final issue was found to be a faulty “crank shaft position sensor”. I believe the old one may have had a lot of rubber build up causing the problem, but for a $65 sensor I just replaced it. Problem solved! Thanks again.

[Tony Athens]

You need one or both..

A vacuum gage on the filter before ( or at the engine connection) the engine, OR 0-30 PSI pressure gauge on the ON ENGINF filter so you can “SEE” what is going on.. If not are chasing what you will not find.

[Fireisland1]

Although you state your fuel filter have been serviced , this appears to be fuel related. The fact that you can throttle back and catch it implies fuel starvation. Now you have to go through the complete system . Hoses, gaskets, fuel pickups etc.

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