Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Hi ,

I've noticed that at any engine rpm the port engine consumption is always around 10-15% over the starboard even idling.
Both have 110 hours and plugs and filters were replaced 20 hours ago. Since I ve had the boat since that last service done when I bought it I can't tell how consumption figures were before.
I get the values via EVC gauges and gallons left at tanks matches the readings. Both engines start right away and run smoothly.( it's a Regal 3760 2010)

Is this normal or I should look into something? (Bad filters, gas, etc?)

Thanks

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Swap the wiring from the sensors, engine to engine and try again.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Have both engines checked out with a scan tool and compare the readings. It could be as simple as the ECT showing the engine is running cold when it isn't and the ECM adding extra fuel for cold running.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Would one motor run a little differently if it was getting 10% more fuel? Not that I know anything about these powertrains, but I find this question interesting. Do they both draw from one, single fuel tank?

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Each engine has its own fuel tank so I was thinking about an ethanol related problem (I believe last time fuel truck got out of non ethanol fuel so it might have put a different blend in one of the tanks but I dont recall exactly in which one).

Now that Don mentioned temperature, the port engine takes more time to reach its working temperature compared to the other one but (I assume because water heater system is tied to its cooling system) but once they are at the same temperature the difference remains.
I will have it checked because I believe that the problem is related to temperature .

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Not referring to the gauge reading you see at the helm, this is a sensor the ECM reads.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Don S said:

Have both engines checked out with a scan tool and compare the readings. It could be as simple as the ECT showing the engine is running cold when it isn't and the ECM adding extra fuel for cold running.

Click to expand...

Here is a chart to which the Oracle is refering to. As you can see the ECU delivers less pulse rate as it warms up.

Water Temp
Deg F Multiplier
0 2.50
50 2.00
100 1.50
150 1.00


Throttle % Multiplier
25 1.50
50 2.00
75 2.50
100 3.00


Air Temp
Deg F Multiplier
0 1.10
50 1.05
100 1.00

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Hi Don,

I checked the on line parts list and I saw that the 8.1 has two temperature sensors , one on each side of the engine (on top of each manifold). Does the ECM reads both or one is for the gauge and the other one is for the ECM ?
Since I dont have an SCAN tool at hand I was thinking in comparing both engines sensor readings with an ohm meter. Anyway Ive always wanted an scan tool so I wonder if an standard OBD II tool will be good for these engines. BTW, where is the tool connection port on these engines?

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

so I wonder if an standard OBD II tool will be good for these engines.

Click to expand...

Nope, they aren't setup to read marine engines. You need one of these. http://www.rinda.com/marine/mtspec.htm#techmate

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Ups I realized that EVC requires an special tool (vodia scan tool ??) , I will have to check on the sensor values with my multimeter then.
Dealer is busy for the next two weeks so I want to do something on my own in the meanwhile.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

I use an analog voltmeter to compare injector pulse widths when checking fueling problems.
Put it on a DC scale and it will give you a rough idea of injector duty cycle.
If it says zero, then the pulse width is zero.
If it says 5 volts then the injector is locked open at 100% duty cycle.
If the two engines have different values when run at the same RPM...then you likely have an engine electronic problem.
If they are the same then you either have a drivetrain problem or (most likely) different fuel pressures on the engines.
If the fuel rail pressure on one engine is 40 psi and it's 44 psi on the other...check/adjust the fuel pressure regulator.
Actually, I'd check fuel pressure before I started messing with any wires.
Fuel pressure regulators are mechanical devices and can drift as they age.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Thanks for the feedback, i will try swapping the Coolant Temperature sensors first because it looks as the easiest thing to do.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Here.. below is pdf on how marine fuel injection works have a read. It is not a guide for your exact ecm and software type but there is very little difference on how the WHOLE system works. You will find that there are not that many components in the system but it illuminates how they work together..swapping parts is expensive

http://www.mdmotors.ru/netcat_files...akteristiki_sistem__EFI__MEFI__MPI__alb_2.pdf

Here is a example page 77

a driveability concern still exists after following the diagnostic circuit check and reviewing
“Troubleshooting,” an out-of-range sensor may be suspected. Because of the unique design
of the EFI system, fail-safes have been incorporated into the ECM to replace a sensed value
with a default value in the case of a sensor malfunction or sensor wiring concern. By allowing
this to occur, limited engine performance is restored until the vessel is repaired. A basic understanding
of sensor operation is necessary in order to diagnose an out-of-range sensor.
If the sensor is within its working or acceptable parameters, as shown, (Figure A) the ECM
does not detect a problem. If the sensor should happen to fall out of this “window,” a code will
be stored. A known default value will replace the sensed value to restore engine performance.
If the sensor is out of range, but still within the operating window of the ECM, the problem will
go undetected by the ECM and may result in a poor driveability condition.
A good example of this would be if the coolant (ECT) sensor was reading incorrectly and indicating
to the ECM that coolant temperature was at 20? F, but actual coolant temperature was
175? F. (Figure B) This would cause the ECM to believe that the engine was running cold. The
ECM would then control the fuel injectors to deliver more fuel than was actually needed and
result in an overly rich, rough running condition. This condition would not have caused a code
to set as the ECM interprets this as within its range.
To identify a sensor which is out of range, unplug it while running the engine. After approximately
two minutes, the diagnostic code for that sensor will set a code, and replace the
sensed value with a default value. If at that point a noticeable performance increase is observed,
the diagnostic testing code chart for that particular sensor should be followed to correct
the problem.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Datkine said:

I use an analog voltmeter to compare injector pulse widths when checking fueling problems.
Put it on a DC scale and it will give you a rough idea of injector duty cycle.
If it says zero, then the pulse width is zero.
If it says 5 volts then the injector is locked open at 100% duty cycle.
If the two engines have different values when run at the same RPM...then you likely have an engine electronic problem.
If they are the same then you either have a drivetrain problem or (most likely) different fuel pressures on the engines.
If the fuel rail pressure on one engine is 40 psi and it's 44 psi on the other...check/adjust the fuel pressure regulator.
Actually, I'd check fuel pressure before I started messing with any wires.
Fuel pressure regulators are mechanical devices and can drift as they age.

Click to expand...

Now that never crossed my mind.....Are you referring to running a engine at a constant 2500 and trying to take a longterm look or averaging the volt signal and comparing the two engines at the same rpm???...Better have a digital read out I need to try this

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

If you use an analog meter the inertia of the needle assembly will average the pulses into a steady reading that reflects the duty cycle of the injector.
If the injectors are rated for five volts drive voltage then when the duty cycle is 100% the meter will read 5 volts.
With no input pulses the meter will read zero.
If the injectors are at 50% duty cycle the meter will read close to 2.5 vdc.
Won't work with a digital meter unless it has a duty cycle scale.
This duty cycle averageing with an analog meter is the same as occurs in an old analog dwell meter used with points.
Ya gotta love old school tricks.

For this boat, you would need to get it on plane and be running at about 50-60% throttle.
Check the duty cycle on one engine and note the rpm.
Get the other engine to that exact rpm and check it.
A 10% duty cycle difference would be like .2-.3 volt difference.

Of course, if you can tap into the ecu it will do this for you.
You can check to see if your injectors are firing with a 12 v light bulb if you are in a jam.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

I question the idea of using an analog meter or light bulb to test an EFI system.
ALL the EFI manuals caution against using a meter that has less than 10 megaohms input impedance and a test light that draws more than 300 mA of current.
Might work might not ---- but your risking a very expensive ECM?
Also might explain some of the ECM?s I?ve replaced due to bad injector driver circuits.

xixp is your boat inboard powered with transmissions?
Some transmissions have more friction when run in reverse and that?s how some of them get one prop to spin in a different direction.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

muc said:

I question the idea of using an analog meter or light bulb to test an EFI system.
ALL the EFI manuals caution against using a meter that has less than 10 megaohms input impedance and a test light that draws more than 300 mA of current.
Might work might not ---- but your risking a very expensive ECM?
Also might explain some of the ECM’s I’ve replaced due to bad injector driver circuits.

xixp is your boat inboard powered with transmissions?
Some transmissions have more friction when run in reverse and that’s how some of them get one prop to spin in a different direction.

Click to expand...

The 300 ma limit is reasonable and won't be exceeded when using a small 12v bulb.
The 10meg ohm spec is meaningless...typical injector impedence is 8-12 ohms.
That means the injector will draw (I=E/R) about 1/2 amp when locked open.
Most ECU driver failures are manufacture related according to a GM engineer friend from Delphi.

I don't understand your comment on friction at all.
It takes gears and clutches to make a transmission work.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Hi Datkine,
My post was aimed at other people that might read your post.
I’ve found over the years that some of the people that come to this board looking for advice don’t have the knowledge of an EFI system that you do. The point that I was trying to make is when a person decides to start coming up with their own troubleshooting methods they really need a good understanding of how the system works. That’s why I said “might work” I’ve never tried your method because the owners of the marinas that I’ve worked for don’t seem to like it when the mechanics blow up a $1000 ECM because they didn’t follow the manual. The instructors at the factory schools do teach us troubleshooting methods that aren’t in the manual. They have never mentioned your method --- but they do assume that we will have access to the factory recommended tools. That’s why I said might work.

“The 300 ma limit is reasonable and won't be exceeded when using a small 12v bulb.”
Sorry didn’t know you meant a small light bulb. All I know is that the circuit tester that I was using before EFI came out didn’t meet the 300mA spec and I had to buy one that did.

“The 10meg ohm spec is meaningless”
Once again maybe it is meaningless, it’s possible that the first person to write a EFI manual just threw that in because he didn’t know what he was talking about and all the rest of them just copied. But did I mention the marina owners and service managers who seem to take it personal when a mechanic burns up $1000?

“Most ECU driver failures are manufacture related according to a GM engineer friend from Delphi.”
Maybe – I just know that when MerCruiser, Volvo, PCM ect. Ship me a ECM under warranty they want me to test the harness and actuators that may have caused the ECM to fail before I plug in the new ECM.

“ I don't understand your comment on friction at all.
It takes gears and clutches to make a transmission work.”
Some boat inboard transmissions use planetary gears to reverse rotation so when you have more gears spinning you have more friction and when you have more friction you use more gas. I’m not saying that’s what’s causing his 10% more fuel burn. I’m just trying to get the point across that maybe he should look at that or shaft log friction or fuel pressure being different between the two engines. Or maybe even swapping the ECM’s from one engine to the other. Before using an analog VOM or light bulb to find out if one ECM is commanding a longer pulse width than the other ECM.

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

Hmm with efi getting aged in our boats and not well understood maybe its time for a efi section....calm down now just a thought..

Re: Port engine consumes 10% than starboard , why? ( 8.1 gi 2010)

At least boats don't have closed loop to complicate things.
I went through the EFI on my 5.8 Ford and changed out the needle in the float bowl.
Some of these older systems are a bit strange.