Mercruiser MPi fuelling self adjustment

[QBhoy]

And 95 is normal here. Not super.

 

[QBhoy]

Yep, same rating, RON, as here. The US post on the pumps the average of RON and MON (motor octane number). It can't be different, because the RON and MON are STANDARDIZED ratings, standardized worldwide.

This is a clip from a document going into a lot more detail if you are interested, but this is the important line....



From that you can understand that it doesn't matter where you are in the world, if the pump says 'RON' it's the same RON as anywhere else in the world. (BTW, I have seen 76RON in some parts of the world. )

Read the full document -> [/FONT]http://www.csgnetwork.com/octaneratecalc.html

Also, read this article from the UK on exactly what fuels you have and what numbers you see on the pumps.... (You don't have 91 RON, so use 95...)

https://www.simplemotoring.co.uk/car-fuel-types/ (and your Mercruiser engine isn't much more than a car engine at the end of the day. A few safety features and a milder cam and that's pretty much it....)

In Aust, we have 91, 95 and 98. Standard, Super and Premium. It appears in the UK you only have Super and Premium. But the 95 you have is the same as the 95 I have.

Here's a clip from the Owner's handbook for your Merc engine....



Chris......

Your very statement above at the top says what the deal is. It’s an average between the two the us uses. The U.K. use the actual RON figure. It’s a different system. So the average of Ron and Mon are not used here.

 

[QBhoy]

US uses (R+M)/2 method

however 87 octane on the (R+M)/2 method is the same fuel as 91R in the UK...... its the low-grade pump swill in both countries........ also the minimum swill the boat is designed to run on.

stole this from here http://www.pencilgeek.org/2009/05/oc...nversions.html

Actual octane rating table

EURO RON	MON	US: (R+M)/2
90	83	86.5
92	85	88.5
95	87	91
96	88	92
98	90	94
100	91.5	95.75
105	95	100
110	99	104.5

Formula for converting EURO to US rating
I've also come up with a pretty good formula that approximates US octane rating based on EURO RON rating, and visa versa. The formula is US=RON*(21/22):

EURO RON	US (R+M)/2
90	85.9
92	87.8
95	90.7
96	91.6
98	93.5
100	95.5
105	100.2
110	105

Formula for converting US to EURO octane
And reversing that forumula, wet get: RON = US*(22/21)

US (R+M)/2	EURO RON
87	91.1
88	92.2
89	93.2
90	94.3
91	95.3
92	96.4
93	97.4
94	98.5
95	99.5
96	100.6
97	101.6
98	102.7
99	103.7
100	104.8

That’s exactly the system. We don’t get a 91 here. But a 95 Ron instead. There is no euro 91 here either. Not sure where you’d get that. Maybe Eastern Europe or something.

 

[achris]

And 95 is normal here. Not super.

So use that!

 

[Scott Danforth]

That’s exactly the system. We don’t get a 91 here. But a 95 Ron instead. There is no euro 91 here either. Not sure where you’d get that. Maybe Eastern Europe or something.

so use the 95 RON, its more octane than the motor is tuned to use. No need ever pay for higher

 

[muc]

While high octane will not hurt the motor, it can reduce amount of available power. The lower octane fuel burns faster and thereby being able to release all the power contained within. Higher fuel burns slower and may not get a complete fuel burn in enough time to get it all

That is really the only answer that can be given, until other questions are answered.


MEFI or ECM 555 or PCM?
Catalyst or speed/density?
IAT, TMAP or none
mean best timing program installed or not?
one knock sensor or two?
what reluctor wheel is on the crankshaft or is it using the distributor for reference?

A few MerCruiser engines will set a fault code and go into power reduction if the fuel has too high of an octane rating.

Once a engines octane requirements have been met, any increase in octane will usually result in less power.

I would think that reed vapor vapor pressure has a bigger effect than octane in power output.

 

[QBhoy]

So use that!

I do Chris. 99% of the time. Just sometimes I pass a petrol station that has 99 for the same price as my local has 95. And like the idea of super being through it before the storage. Sorry for being a little hot headed last couple of days...been crazy with work and not having a boat in the water to relieve the mind, come Friday ! Feel rotten !

 

[QBhoy]

That is really the only answer that can be given, until other questions are answered.


MEFI or ECM 555 or PCM?
Catalyst or speed/density?
IAT, TMAP or none
mean best timing program installed or not?
one knock sensor or two?
what reluctor wheel is on the crankshaft or is it using the distributor for reference?

A few MerCruiser engines will set a fault code and go into power reduction if the fuel has too high of an octane rating.

Once a engines octane requirements have been met, any increase in octane will usually result in less power.

I would think that reed vapor vapor pressure has a bigger effect than octane in power output.

Thanks Muc for the interested reply.

as far as I know;

No Cat
not sure on knock sensor (but I assume if it does then this would only have an influence on timing at full throttle...perhaps thinking it wouldn’t knock at cruising speed in most cases)
crank shaft sensor definitely there
ecm 555 I think
crap cap Diz cap
has a fancy cam fitted at time of fit out in factory. Not well suited at anything under about 4000 rpm though. Quite lumpy low down. Not sure if that is normal or not as a result.

 

[QBhoy]

so use the 95 RON, its more octane than the motor is tuned to use. No need ever pay for higher

I get you Scott. But maybe one of the reasons for asking is perhaps if the motor is able to adjust to suit higher octane...it might well be able to optimise itself to suit...as opposed to your suggested, that it’s tuned to only suit a lower fuel ?

 

[Scott Danforth]

I get you Scott. But maybe one of the reasons for asking is perhaps if the motor is able to adjust to suit higher octane...it might well be able to optimise itself to suit...as opposed to your suggested, that it’s tuned to only suit a lower fuel ?

Unless you reprogram the FAST (Fuel, Air, Spark Timing) tables and change the combustion mix (compression, cam timing, piston profile, combustion chamber, etc) to use better than the minimum octane, it cant benefit from higher octane

 

[QBhoy]

Unless you reprogram the FAST (Fuel, Air, Spark Timing) tables and change the combustion mix (compression, cam timing, piston profile, combustion chamber, etc) to use better than the minimum octane, it cant benefit from higher octane

Can that be done easily with a rinda?

 

[achris]

Can that be done easily with a rinda?

No. Not easily, not with great difficulty. Rinda software can't do it at all. It's not designed for that.

Also, it might seem nice to put the higher octane in when it's the same price, but it's actually a backwards step. As AllDodge explained, the higher octane fuel burns slower (resists knock more, but...)...

There's a fallacy around that higher octane fuel has more energy in it. It does not. It has the same, exactly the same, it's just more resistant to knock. And because it burns SLOWER, less energy is available to do the work on the piston at the right time..

A few weeks ago a friend asked me why one of his friends got a worse fuel economy when running higher octane fuel. I had forgotten about the slower burn rate, and until I read AD's line regarding that, I was stumped. Then it made sense.

Hope this helps.

Chris......

 

[Scott Danforth]

Can that be done easily with a rinda?

NO, Rinda is a diagnostic software

If you had development software and a dyno to tune it properly........you still need to change pistons, cam, etc

 

[muc]

Can that be done easily with a rinda?

I have always used the Mercury CDS-G3 to load new calibration files, so I’m not 100% sure Diacom will do it. But I think it will do it for a ECM 555 easily.

But first you would need the new file to load and I don’t think Diacom will build the files.

 

[Lou C]

What the modern technology can do is react to the effects of the fuel octane you are using. So if your engine does not knock it will keep the timing at its preset level of advance; if it does it retards timing till it does not hear knock. All the ECM can do is respond in a programmed way to inputs form sensors. That said I’d have no concern using fuel of the octane level specified by the manufacturer. This was more of problem on engines with no knock sensor and no way of adjusting timing in response to knock that can be caused by things like carbon build up or lean fuel mixtures.
BTW both gas docks I use have only one choice of octane; 93 US level. Probably overkill for the majority of marine engines.

 

[Lou C]

And if the original concern was about storage in the off season, it is more of an issue if you have to use E10 gas as we do. If you’re using straight gas I’d say you have nothing to worry about with a 4-6 month storage period

 

[alldodge]

But I think it will do it for a ECM 555 easily.

But first you would need the new file to load and I don’t think Diacom will build the files.

Hey, can you provide any insight as to how this can be done? There would be many that could use the info. I know where not talking about PCM 555. Thanks

 

[QBhoy]

No. Not easily, not with great difficulty. Rinda software can't do it at all. It's not designed for that.

Also, it might seem nice to put the higher octane in when it's the same price, but it's actually a backwards step. As AllDodge explained, the higher octane fuel burns slower (resists knock more, but...)...

There's a fallacy around that higher octane fuel has more energy in it. It does not. It has the same, exactly the same, it's just more resistant to knock. And because it burns SLOWER, less energy is available to do the work on the piston at the right time..

A few weeks ago a friend asked me why one of his friends got a worse fuel economy when running higher octane fuel. I had forgotten about the slower burn rate, and until I read AD's line regarding that, I was stumped. Then it made sense.

Hope this helps.

Chris......

chris there have been many tests on dyno which see bhp improvements, when using super over regular unleaded fuel. Without altering anything but the fuel in the tank.

 

[achris]

In that case, the engine was probably designed to run on the higher octane fuels. I venture to suggest that an engine designed to run on 91 would perform poorly on 99 for the reasons I have suggested (already seen that on a few cars in Australia)...

Chris.....

 

[muc]

Hey, can you provide any insight as to how this can be done? There would be many that could use the info. I know where not talking about PCM 555. Thanks

In the upper left corner of the Diacom screen is the tools drop down menu for downloading the file. If you’re asking how to build a new calibration file, I have no idea. They are sent to us by the manufacturer and are tightly controlled.