Fuel Consumption port vs starboard engine

I have a 2006 38' Sundancer I was having a problem with one engine burning more fuel. I found a spark plug wire off and another half off. It would be worth checking
 
Shaun Quilty said:
I have a 2006 38' Sundancer I was having a problem with one engine burning more fuel. I found a spark plug wire off and another half off. It would be worth checking
Click to expand...

Yeah... better check those spark plug wires on the QSM-11's... never know when one might pop off... Maybe you should call Cummins and have them come out and tell them to bring a new set of spark plug wires just in case.

Good grief... where the hell did that come from? Just when you think posts can't get more stupid.

"Sometimes it's better to keep your mouth shut and let them think you are stupid than to open your mouth and let them know you are stupid."
 
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Gary,
I put new Champion Platinum Series Spark Plugs (Herr Rudolf Diesel Signature Series) in my C Series and my fuel burn decreased by 20% at the same RPM. This cool mod included ceramic plug wires, and a new distributor cap and rotor. You may want to try this on your Qs and see if that rather gaudy fuel burn decreases a bit-
Sure, the plugs don't last as long with the whole 23:1 compression thing, but I think the improved fuel economy is worth it.
Next step: Nitrous injection into the turbochargers.

Get 'er done

Your pal,
Skip
 
Maybe one tank has a higher ratio of Ethanol in the fuel mix?:huh:


:grin:
 
Getting back to WOT, the OP needs to warm up the engines then disengage the synchronizer and run the boat with both engines running at full throttle. He should then report the top ROM acheived by each along with load percentage.

I don't know about Cummins, but CAT also has a spec. for bare high idle. This is the RPM the engine should acheive at WOT throttle with the gear in neutral. If Cummins provides such a specification, it can help to diagnose if the problem is engine related or gear/shaft/suffing box/prop related.
 
Sea Gull said:
Getting back to WOT, the OP needs to warm up the engines then disengage the synchronizer and run the boat with both engines running at full throttle. He should then report the top ROM acheived by each along with load percentage.

I don't know about Cummins, but CAT also has a spec. for bare high idle. This is the RPM the engine should acheive at WOT throttle with the gear in neutral. If Cummins provides such a specification, it can help to diagnose if the problem is engine related or gear/shaft/suffing box/prop related.
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The QSM-11's will not go above 2330 as the electronics limits the RPM to that regardless of the load... That test won't work here. He's hitting that but with less fuel being burned than should be... it's either got too little load on it or has discovered a way to increase the efficiency (maybe with a magic carburetor?) of the engines.

If the starboard engine is underpropped, it's also going to put more load on the port engine as well. However, his port engine numbers (the one burning more fuel) look right on the money...

I would also be curious what the boat's speed is at 2100 RPMs.. Although subject to how loaded up the boat is, if it has half fuel or less, it should get to 26+ knots. I suspect it's not getting there....
 
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Ah, OK. I'm just vying for the stupid post award. I would think the electronic governor would allow the engine to spin up higher in an unloaded state. They don't seem to allow much leeway in propping assunming rated WOT is 2300.
 
Sea Gull said:
Ah, OK. I'm just vying for the stupid post award. I would think the electronic governor would allow the engine to spin up higher in an unloaded state. They don't seem to allow much leeway in propping assunming rated WOT is 2300.
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I have no idea what parameters go into the "Engine Load" number on the electronic display but proper propping means the engine hits 100% load at 2300.. It's a nice system to have because I know that at rated cruise (2100 RPM) I should see 80%. If the boat is really loaded down and I see 80% load at 2000 RPM, I know to stop there and not blindly run at 2100 RPM.

I actually run around 75% load... It's interesting because I'm not sure that getting to rated WOT is impacted much by the loading/propping on this boat. I've had the boat full of fuel, jet ski on the back, and 4000 pairs of my wife's shoes and was running at 80% load at around 2000 RPM and it still hit 2330 RPMs at WOT... so I've never seen where WOT was diminished by loading on my QSM-11's (other than a crapped up bottom). I still follow the load meter though. Sea conditions also will dictate slowing down to keep the load under 80%... Climbing over those damn swells last year on the way to Block Island had my load meter going from 95% to 60% going up and surfing down...

Who knows the history of this boat though. Maybe both props were underpropped and the prop shop put the port prop where it should be and left the starboard one underpropped... Don't really know... other than the starboard numbers are wrong.
 
Those fuel burn curves represent a proper loading of the engine (read the details at the bottom). The electronics will dump less fuel in the system when there is less load...

Also, you'll note that the spec sheet for the QSM engines listed on that website do not match what is in a stock 2003 480DB.
 
Four Suns said:
I have no idea what parameters go into the "Engine Load" number on the electronic display
Click to expand...
At cruising speeds, it seems like a linear relationship with fuel flow. In my case 100% = 50 GPH (combined), 80% = 40 GPH, 60% = 30 GPH. Depending on the conditions (load, etc.) the same RPM will be associated with a different fuel flow and thus a different "% Load". This is only an observation, I don't know this for sure.

Also, the linear relationship falls apart at lower speeds. For example, at 6 knots, my combined fuel flow is under 3 GPH, but the % load is around 23%. Go figure.
 
Thanks for all the suggestions guys. The Boat Yard has offered to pull the boat and the props. I think I am going to take them up on it after the 4th. I will update you all on the results.
 
Update:
The retuning of the props solved the problem. The fuel on the consumption on the port engine is now within 1.4 gal/hr of the starboard engine at 2100 rpm's. FOUR SUNS has posted that this is normal. The overall fuel consumption has been reduced by 3.1 gal/hr at 2100 rpm's. Both engines now reach 100% load at WOT.

I has told that when the props were checked that it was discovered that one of the wheels was 2 lbs heavier.
 
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