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I have noticed that my port engine (F300) has been burning more than fuel than starboard, usually about 10 gals more on a 170 gal trip. Took a longer trip (216 gal total) and fuel gauge (which has been accurate so far, don't think it's a bad sending unit) showed port engine burning about 120 gal and the starboard engine burning 95 gals. Have not detected a miss but did try running each engine alone and starboard reached 13.8mph and port only reached 12.7 mph. What are the chances this is just a spark plug problem (they have 670 hrs - I typically get 1000 hrs before changing). Observed engine run without cowling (on trailer) and no visible or scent of a gasoline leak. Anybody have any thoughts? Experience something similar?
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What are you using to determine fuel consumption? Total and GPH. -
I would swap the fuel lines to make sure the usage moves also just to rule out the devicesComment
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GPH - I use the Yamaha flow meter (but I have not reviewed for each engine - #s I quoted were mph). The actual difference in fuel consumption is by gas gauge meter and then verified by actual gallons put in.Originally posted by boscoe99 View PostComment
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Originally posted by bjd76 View Post
F300 engines, I doubt that there are actually flow meters -
but rather Command Link gauge reporting what the ECU "thinks" its using
which may be absolutely correct...Comment
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I did not think about no flow meters since he mentioned sending units.
spark plugs a cheap enough.
I would change them and then see if that gets the motors back to even burn ratesComment
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the ECU can calculate and display fuel burn,fuel burned for that trip and estimated fuel.
use the command link wisely.
it also may help us if you can tell us if this is a 5.3L or a 4.2L
may make a difference in my advice.
the ECU is usually dead nuggets on the fuel consumption.
but your going to have to run the engines with YDS or the dongle attached to see why the ECU is upping the fuel burn.
could be the engine is running cold,could be the rail pressure is high,could be an issue with cam timing or a clogged OCV filter.
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Rodbolt - the ECU "doesn't know" what the rail pressure is, yes?Originally posted by rodbolt17 View Post
so the reported fuel burn assumes rail pressure is in spec?
if it only "knows" rpms and "how long it thinks injectors are open"
seems to me, in a "high rail pressure" case, the fuel burn would be under-reported
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yes, the ECU assumes rail pressure is in spec. not high or low.
the ECU KNOWS how long the injectors are open and does the math.
it has long amazed me that since rail pressure is absolutely critical, no one ever used a transducer to tell the ECU the exact pressure.
and the OP really needs to quit hopping about with meters and mph.
need to look at GPH and RPM.unlike old two strokes and early 4 strokes the command link does not use a flow sensor.
it uses injector on time.
it assumes rail pressure is ok.
Yamaha wont tell us if the fuel calculation is based on a truth table or does it take in RPM.
Injector on time is a function of engine speed,engine load,air temp,air density,engine temp and throttle angle.not real sure how cam timing affects on time or if it does at all.
a clogged OCV filter may make an engine burn more fuel for a given mid range RPM.
I would want to see the YDS reports compering both engines at idle,1000,2000,3000,4000,5000 and 6000 RPM.
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And neither is the voltage to the injectors monitored. Voltage variances have been known to affect fuel delivery rates.Originally posted by rodbolt17 View Post
Obviously, in the scheme of things, it must not really matter. The system works and works well.
I still see a benefit of monitoring actual fuel flow through the fuel hose. It should agree more or less with what the engine is calculating fuel flow to be. If there is a large variance, or if the two systems start disagreeing, whereas they once were in agreement, it is a heads up as to something going amiss.
There is no such thing as too much information IMO. Well, for some there might be. For them just a light is sufficient. If they will even pay attention to it.
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never thought about valve timing,
these motors are getting more and more complected
fuel pressure should be simple to checkComment
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Interesting to me how different companies go about designing their motors. Some for instance will monitor exhaust gas temperatures and exhaust gas air/fuel ratios to obtain feedback inputs to the ECU. Some don't. Some use a speed/density system whereas some will measure mass air flow.Comment
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which is the best?
and then which is the cheapest to produce?Comment
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Many thanks to all for the comments. Some clarifications... yes, the fuel consumption reference is through the Command Link/ECU and it has been dead on for years. I did not look at it for fuel consumption during the single engine test noted previously - should have.This issue started about 9 months ago and I figured it may be because of sea direction, trim angle off, or because it's a counter rotating engine. Nothing has been physically added to boat to cause this issue. This was a more noticeable difference and seems to indicate a worsening problem. BTW, my typical trip is running at 34-2800 rpm for 8-10 hours and from idle to 1000 rpm for 14-16 hrs. I have changed all spark plugs but will need to run boat to determine if performance and fuel consumption has changed. Have not been able to get mechanic to hook up PC while running and feel I need to do so before my next typical 240 mi round trip. Searching the forums, some past issues/suggestions for similar problem were:
- low pressure fuel pump problem and dumps gas in crank
- Leaking float valve (carbureted engine only?)
- Cracked pick up tube in fuel tank so sucks more air/gas
- Fuel injectors and/of VST filter clogged/issue
- "Dropped" cylinder or two
- Bad coil
About the same time as this fuel difference surfaced I have had to stop filling fuel tanks about every 8 gallons or it will act as if the tank is full and burp/shut off. I attributed this to a kink or low spot in vent line. starting to wonder now if they are related.... There is no visible gas or fume smell with this problem. I need to get this fixed so I don't mss the next weather window as they are few and far between this time of year!!!Comment
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Rodbolt is a Yamaha master tech, so pay attention to his postsComment
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