SLight difference in RPMs at WOT / QSB480HO's

[DF470DA]

just looking for a little feedback as to what would cause my starboard engine to run 60 to 80 rpm less than my port which is running about 3440 at WOT which is where it is supposed to. I have 103 hours on the engines, and also that same engine when first turning on my keys to activate the ignition the prestart noise which I figure is fuel injection goes on for what seems like 30-45 seconds? Any help is greatly appreciated, thanks...Don

 

[src]

Seems like you are probably worrying over nothing. That's a 2.3% difference, and is probably well within the tolerance for "normal".

 

[BigBoysToys]

Could be a slight anomaly on a prop, dirty fuel filter, I even had a slightly flattened spot in a fuel line where it was bent just a little too tightly from the factory and it affected WOT rpm. My guess is its probably nothing to worry about.

Sent from my RM-860_nam_usa_100 using Tapatalk

 

[alnav]

Not sure I can add anything to this but would encourage you to use the Cummins warranty service to the max extent; I assume you are still well under the 2 years of coverage. If you call a tech in to evaluate this problem I don't think it will cost you anything but the tech will likely find something that's not perfect and fix it for you. You should also try to get them out just before the warranty expires, after that you will pay through the nose. I had a slight coolant leak but didn't call Cummins until just after the warranty expired and really regret not coordinating the timing of the service call better because the tech found a couple of things that otherwise would have been covered.

 

[DF470DA]

all good advice, thx Al re the warranty thought, I think that's a good call....df

 

[Time To Relax]

Do both engines rotate in the Same direction? If they do then one gearbox is running in reverse to give you counter rotating props. If this is the case chances are that the ratios foward and revers are silty different causing different engine loading. On my boat one engine is running at 2. 03 to one and the other is at 1.99 to one

 

[fwebster]

Is this a Zeus boat?

The problem isn't the fuel filters. Diesels require lots of clean fuel; they either run or not. If a fuel filter has a restriction, the engines will gradually slow down until it kicks an error code, but it will not just slow down 80 rpm and keep running.

This sounds a lot like a prop strike that has caused the prop set to have enough disturbance to slightly affect efficiency.

 

[DF470DA]

thanks Frank - it is a Zues boat...and I think you may be on to something as I do notice a slight vibration at certain rpm's in the range. I'll have the props looked at when I pull the boat for winter storage....df