Temporary loss of power on Cummins QSB 5.9

[driver0606]

You solve one problem and up comes another. Hey Ho, I guess that's boating.
I have just completed an hour's run in my Azimut 43 fitted with twin Cummins QSB 5.9. The fuel filters were newly changed. After about 30 minutes at 2400 revs/min., the starboard engine started to lose power and surge and then would only run smoothly at not more than about 1000 revs/min. I let it idle for a while at 600 and it stalled, but restarted easily. “Check engine” appeared on the display. Classic blocked fuel filter symptoms, but the filters were new and the Racor glass was clear. I switched it off for a few minutes, then restarted and it ran normally and cruised at 2400 for a further 20 minutes, so it could not be blocked filters.

Any ideas, please?

 

[jrudge]

Filter not tight enough. At high rpm sucking lots of fuel and air starts to enter the system. Slow down vacuum decreases and air does not enter.

 

[Trundlebug]

Either that or crud in the tank blocking the fuel take off pipe. Engine runs well, sucks fuel then a solid gets drawn towards the pipe and blocks the end, causing classic fuel starvation symptoms similar to blocked filter.

Stop the engine, the solid bit drops away, and off you go again.

 

[PCUK]

+1 Filter problem.

 

[KevB]

Either that or crud in the tank blocking the fuel take off pipe. Engine runs well, sucks fuel then a solid gets drawn towards the pipe and blocks the end, causing classic fuel starvation symptoms similar to blocked filter.

Stop the engine, the solid bit drops away, and off you go again.

I've had exactly that. For some stupid reason the pickup pipes on my engines had a fine wire gauze over the end of the pipes and over the years these slowly blocked till something similar to the OP happened.
Removed the gauze and not had a problem since.

 

[driver0606]

I've had exactly that. For some stupid reason the pickup pipes on my engines had a fine wire gauze over the end of the pipes and over the years these slowly blocked till something similar to the OP happened.
Removed the gauze and not had a problem since.

 

[driver0606]

The filters are tight and that seems unlikely to be the problem as the engine ran fine subsequently. I drained off the bottom of the tank and it was as clean as a whistle. Its not possible to remove the supply pipe as it connects at the bottom of the nearly full tank. Could it be the fuel lift pump?