Does CO trim affect fuel consumption significantly?

A couple of months ago I inspected my sparkplugs and noticed one side was okeyish, but the other seemed too lean. I rebalanced the throttle-bodies to make sure the air intake was as it should be, and also set the CO trim to +3 on Beetle's advise.
Today I re-inspected the sparkplugs, to my delight they are now both absolutely perfect. Light brown 'coffee' colour on both of them, textbook example of good sparkplugs. However I have noticed that since I changed the CO trim & rebalanced the throttle-bodies my GRiSO uses significantly more gas. I'm making fuel-stops noticeably faster, and the dash confirms this: typical highway cruising consumption went from 5.8L/100km prior to 7.1L/100km post.
So I'm wondering if this is possibly related to the CO trim adjustment I did (I have absolutely no idea what CO trim actually does, something with fuel pulse timing?) or is this unrelated to that?

CO trim adds a fixed value to the real-time fuel pulse with. Each increment of CO provides for 100uS of time. So, +1 would add 100uS to the real-time pulse.

For example, a 2500uS pulse at 3000 RPM, would then become a 2600uS pulse. The entire rev range is affected, so each pulse would have 100uS added.

In your case, at +3, you have added 300uS to each fuel pulse.


So, yes, it does affect fuel consumption.

Is that just idle trim? Or does it effect say 2200rpm or past?

All of it.

beetle wrote:

CO trim adds a fixed value to the real-time fuel pulse with. Each increment of CO provides for 100uS of time. So, +1 would add 100uS to the real-time pulse.

For example, a 2500uS pulse at 3000 RPM, would then become a 2600uS pulse. The entire rev range is affected, so each pulse would have 100uS added.

In your case, at +3, you have added 300uS to each fuel pulse.


So, yes, it does affect fuel consumption.

Thanks, so +3 is actually quite significant, increasing fuel consumption by over 11% at 3000RPM, more at lower RPM and less at higher RPM?

Redo your maths. That's 4%.

It has a non linear affect because the pulse widths increase substantially as RPM increases. Therefore, it has a greater impact at idle than it does at say, 6000 RPM.

Where do you spend most of time when riding? 5th gear? Open road? Town? Do you spend much time above 4500 RPM? You want to drop the CO back to +1.

Also, I may be able to tweak the map to reduce fuel usage.

To take the guess work out of adjusting the CO trim I hooked up my AFR meter with a wide band lambda sensor. Starting at idle I set the AFR at 13.5:1 which resulted in a CO value of +6. I then rode the bike and looked at different rpm and the bike was averaging 14.5:1 which is good for fuel consumption without losing power.
I don't really see how you could adjust the CO trim without a CO meter and be sure what the bike is doing. Also on my G1100 the plugs have never been exactly the same colour, the r/h plug always looks to be running slightly weaker. Without two lambda sensors it would would be difficult for me to equalise the two.

beetle wrote:

Redo your maths. That's 4%.

It has a non linear affect because the pulse widths increase substantially as RPM increases. Therefore, it has a greater impact at idle than it does at say, 6000 RPM.

Clear, though however I calculate it I couldn't get 4% (2500 pulse width increased by 300 is a 12% pulse width increase? I obviously don't know enough about this stuff   )

beetle wrote:

Where do you spend most of time when riding? 5th gear? Open road? Town? Do you spend much time above 4500 RPM? You want to drop the CO back to +1.

Also, I may be able to tweak the map to reduce fuel usage.

Thanks! Some first to third gear city riding but most of my time is spend cruising on the highway in 6th gear, about 120-140 km/h at around 4000-4500RPM.

My apologies, I was referring to my example.

Go back to +1 for now. Let me know how that works.

I agree it is a 12% increase at 2500 pulse width but you are not cruising at that pulse width so the percentage increase should be less, but you state a 20% increase in fuel consumption (5.8 to 7.1/100km) at higher rpm, something  doesn't add up.

example:
 4500rpm at 24 degs TPS = 5309 pulse width(pw). Add 300 it becomes 5609, a 5.5% increase in theoretical fuel consumption. Whether it works like that in practice I haven't a clue.

True, but I am not certain the dash gives a 100% correct fuel consumption rate? Also its quite cold here now (around freezing temps), so perhaps its a combination of the co trim, the cold, perhaps even lower tire pressure due to the cold, etc.

I don't know how Mark has set your map to run, the standard map adds as much as 17% to compensate for colder denser air, so there is a dramatic increase in fuel consumption when the weather gets cold.

I thought all the CO trim on GuzziDiag or my other software only adjusted idle CO. Same as the screw on my P8. I have not noticed any more richness on plugs doing chops and looking at them. I wonder if this is just for the 5AM?

Cold weather can alter your consumption by an amount. I find below 10/12 degrees C, my consumption goes up by around 8% or so. The temperature correction table will give you an idea by how much on your map. This table can be modified, however you may end up running uber rich/lean depending on which way you go.

Also prevailing winds can do wonders for consumption, especially in cruise mode. Headwinds alone can add 5% to consumption, and a strong tailwind can improve things remarkably. This is not linear though, as you (well me) tend to go a little faster with a tailwind, because I can.

GuzziSteve wrote:

I thought all the CO trim on GuzziDiag or my other software only adjusted idle CO. Same as the screw on my P8. I have not noticed any more richness on plugs doing chops and looking at them. I wonder if this is just for the 5AM?

Correct, only the 5AM operates this way.





Timothy, if you are riding in very cold temps, Dave & Tony a correct. The fuel is enriched to compensate for the cold air. Both the pressure-air-temp and fuel-engine-temp correction tables will be in affect here.

Thank you Mark, as you know I don't like crunching numbers. Had enough of that w/MyECU, but it's working pretty sweet.

Does all that mean that we need a different map according the different seasons 

Does anyone remember slowly altering the manual choke on a carbed bike. It wasn't difficult and before long the choke was off and all was golden. To achieve this the air flow was restricted (choked) thus richening the mixture, easy.
With the event of fuel injection instead of restricting air flow more fuel is added not just for a cold start  but for changes in engine temperature and air temp/pressure, thus supposedly improving efficiency. If efficiency is measured in increased fuel consumption then progress has surely been made.

Richard_HdS wrote:

Does all that mean that we need a different map according the different seasons 

Joking apart the air pressure/temp table does this for you, if poorly in my opinion. If you look at a dyno chart it usually states the air temperature and pressure at the time the readings were taken. Without very accurate map compensations this is the optimum point, at any other temperature/pressure the results will be different.
Where I live, basically just above sea level with a relatively narrow change in air temperature and pressure it is easy to do away with any compensation in the air/pressure table and run the bike more like a carbed set up.

Thanks for the explanations