Update #1: Significant Fuel Consumption Difference

[bjd76]

Thanks to all who offered advice/suggestions regarding my issue. I thought I would provide an update given that my mechanic has hooked up the PC to see what was going on. First thing we discovered is it is the starboard engine that is burning more fuel. When connecting the wire leads to the Command Link apparently someone had the starboard engine and fuel tank represented by the fuel gauge on the left! He analyzed both engines' plugs and saw 2 from the starboard engine that were worse than the others.

My installation of the new spark plugs were all ok.
With the new spark plugs in and the PC hooked up it

revealed that the starboard injectors were open longer - about 8.5 millisecs and the port injectors open 7.3millisecs (I think I have that right) at my normal cruise of 3600 rpm. We are going to replace the VST filters as start and take a trip and see how that does. If still a major difference he is thinking the injectors or injector screens may be a problem. He thought those scenarios may be more likely than a bad Oil Control Valve (OCV, which Yamaha calls an "oil solenoid if you're looking for it on their engine schematics). I have always bought fuel from the same gas station since I have owned the boat but fill tanks using 2 different hoses (therefore different dispenser filters). If dirty gas or tank bottoms I would have thought it would affect both engines but who knows...

[boscoe99]

As rodnut has noted, injector pulse width varies based on a number of inputs to the ECU. For instance, engine temperature, air temperature, manifold pressure, throttle angle opening, etc..

When comparing pulse widths between two motors it might be a good idea to also see if the input variables are one and the same.

A quick swap of the ECU's might be performed just to see what can be seen when the ECU's themselves are the variable.

The oil control valve does not provide inputs to the ECU. The ECU simply tells them what to do. It does not monitor them to see if they are doing what is told.

Does your mechanic have a Yamaha "boat in the box"? This can be used to measure actual fuel flow to the motor to see how it compares with what the ECU is reporting as fuel flow. It is a conventional Yamaha fuel management meter that uses a sensor in the fuel hose to physically measure the rate of fuel flow.

[rodbolt17]

actually the ECU does monitor the OCV's.
it is called intake cam timing and is displayed in degrees.
the ECU also monitors the port and stbd cam sensors .
were the throttle angles the same ?
you can use YDS to monitor that as well.
code 73 s-oil control valve
code 74 p-oil control valve.
your simply going to have to compare what the ECU's are seeing.

[bjd76]

Thx again for the interest and help. One other thing I forgot to mention is that we again did the single engine test to WOT. And similar to last time, the starboard engine went to 4100 rpm before prop slip/cavitation and Command Link showed about 25 gal/hr fuel consumption. The Port engine again went to 4600 rpm before prop slip/cavitation and showed about 21.7gph. Are the "codes" mentioned to be "input" and the results observed? Thx.

[99yam40]

why would anyone run a twin engine boat on one motor at WOT?

[boscoe99]

why would anyone run a twin engine boat on one motor at WOT?

Damn if I know.

Sounds like the same kind of folk that will run a motor to WOT in neutral. Testing for something. I guess. Don't know what.

[pstephens46]

Good to blow out the carbon from time to time.

[boscoe99]

Good to blow out the carbon from time to time.

Which way?

By running a motor at WOT in an over propped condition or by running a motor at WOT with no load at all? Or is it both?

[pstephens46]

Which way?

By running a motor at WOT in an over propped condition or by running a motor at WOT with no load at all? Or is it both?

Probably easier to remove in reverse. Put in reverse going about 45 mph and blow it all out the intake. Catch it in a towel to keep it tidy. Like blowing your nose.

[boscoe99]

Probably easier to remove in reverse. Put in reverse going about 45 mph and blow it all out the intake. Catch it in a towel to keep it tidy. Like blowing your nose.

Thanks for the graphic thought.

Remember the old days when men carried cloth handkerchiefs around with them. Using the same rag all day, nose blow after nose blow? No thanks.

[rodbolt17]

hey
I wear a belt everyday.
I carry a hankerchef everyday.
when I wear a ball cap I know how the brim works.
I also know how to PROPERLY test an engine.
it actually involves eyeballing it at its failure RPM and load.

[bjd76]

I guess a couple of you are having fun at my expense, yuk it up... It was done under the supervision of a certified mechanic and for a very short duration. It amazes me the assumptions Internet folks make without knowing anything about somebody. There is a big difference in having knowledge and using it to help someone, as opposed to having or thinking one has knowledge and poking fun at someone trying to learn. Your parents/teachers should have taught you that. If you have something constructive to offer please do so. I get enough chuckles at my own ignorance on this issue without your help.

[boscoe99]

I guess a couple of you are having fun at my expense, yuk it up... It was done under the supervision of a certified mechanic and for a very short duration. It amazes me the assumptions Internet folks make without knowing anything about somebody. There is a big difference in having knowledge and using it to help someone, as opposed to having or thinking one has knowledge and poking fun at someone trying to learn. Your parents/teachers should have taught you that. If you have something constructive to offer please do so. I get enough chuckles at my own ignorance on this issue without your help.

We are not laughing at you we are laughing with you. Oh, but you are not laughing.

Seriously though, we are trying to make a point. If one of two motors is run at wide open throttle without a propeller change there is a risk of doing serious damage to the motor. The motor is being lugged. It is way over propped. Yamaha wants the motor to be able to turn at or near 6000 RPM when it is at wide open throttle. By your own comment the motor could only turn 4500 RPM or so. Not good for the motor. Furthermore, it is not a valid test of anything.

Same with running a motor at wide open throttle when in neutral. It cannot validate anything. It can only possibly, repeat possibly, do harm to the motor.

[pstephens46]

As a group we do this often. Just banter back and forth while waiting on the OP to return with more info. Been slow around here. No one intended to insult or cause you to leave.

[zenoahphobic]

Running a dual engined boat on a single engine will in all likelihood produce different results, even to the differences you have found without anything really wrong with any particular engine.
This is because there are differences in how each engine relates to the boat; for example they both rotate in the same direction although the props run opposite to each other.
Moreover the boat probably has not been setup to optimise each individual engine on their own (no one really does). Simply the differences could even be attributed to the differences between propellers.
I would not worry about short term WOT at any revs. This nonsense you hear is to do with possible long term running damage. It is nonsense because say running at half throttle should therefore produce what revs?. Or for any other throttle position? Just think if you were to put a smaller carburettor on the same engine, WOT would now be equivalent to less than WOT with the previous carburettors!
So there is room to optimise each engine; running the existing propellers is meaningless. It's a catch22 to do this. A very difficult thing to balance them!
All that said, I suspect the problem lies in the boat. Things like weight distribution, damage to the hull etc. etc.
I would critically look at what might have changed.