Lot's of talk on MPG and octane and can the Fit tell the difference in the grade of fuel being used.

87 is published as the minimum octane to be used in our Fit's, but what if you burn 92?
Folks have speculated and a few 'tuners' have insisted but how does a guy like me, running a stock 2010 Fit, know?

I recently purchased the UltraGague.
Nice little unit that monitors lots of things coming out of the ECU.
What I've been looking at are the long and short term fuel trims.

My research has told me regarding FT:
1) Fuel trim is what the ECU uses to adjust injector duration.

2) When a manufacturer sets up a base engine tune the ECU is going to be set [internal drive maps] to provide fuel trim as close to zero as possible using the recommended fuel octane.
This is important to provide the ideal 14.7:1 fuel air ratio EPA requires for catalytic converter efficiency.

3) Fuel trim values are a % above or below zero and are constantly changing under operating conditions.
Long term values are part of the basic injector duration calculation and are stored in the ECU's memory.
Short term Values are a temporary correction factor and are not stored when the ignition is shut off.

4) Fuel trim values that are negative are decreasing the injector duration and positive values are increasing the injector duration.

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So here's what I'm thinking.
Discussion has been made regarding the ability of the Fit to 'compensate' for fuel octane.
I run 87 octane fuel. Here's a typical start-up:

COLD START at idle Fuel Trims not driving, allowing engine to warm-up
Free Air Temp: 19F
Coolant Temp: 24F
idle: 1375RPM
-------------------
LT: 9.38 - stored value
ST:-1.6 -- CT:29F
ST:0 ----- CT:60F
ST:2.3 --- CT:70F
ST:1.56 -- CT:80F
ST:0.78 -- CT:90F
ST:0.78 -- CT:100F
--------------------
15mile drive at idle fuel trims
Free Air Temp: 24F
Coolant Temp: 181F
LT: 7.03
ST:2.34

est MPG 32
idle: 702RPM

Driving I see avg LT: 9.8 ST: 9.8, although ST vary from zero to 14.
--------------------
I plan on switching to premium fuel and see what effect it has on the fuel trim.
My guess is it will bring the %'s closer to either side of zero.
If so then is it safe to say the Fit's ECU is smart enough to adjust to the use of premium fuel?

Anyone else monitoring fuel trim vs fuel grade???

I'm hoping to gather results while winter is still upon us to keep the keel even - if you get my drift...

K_C_

 

I just got mine and this is what I observed so far. I use Amoco(BP) ultimate 93 octane. When I first plugged it in the temperatures out side was in the 20's and the long term fuel trim was -3.1 and the short term was -2.3. The temps fell and the LT went to 0 and but the ST was still pulling fuel. At start up it pulled -7 ST. I dont have the temps but it didn't change until I turned on something or started driving. I also noticed the EGR did not flow until the intake temps got to 32 and then there was a bigger swept in ST. Right know the LT is -3.1 and the ST moves 15 to -15 depending on where the pedal is.


Here is help to understand fuel trims Tech - Closed Loop, http://www.autoshop101.com/forms/h44.pdf, http://www.autoshop101.com/forms/h48.pdf

 

You nailed it with that link SB.

One other thing to keep in mind is that the ECU is actually looking for target lambda. Because you can have the same lambda between two fuels like Ethanol and Gasoline and have wildly different AFRs.

Lambda voltage ranges from .6v-1.2v usually on a Nernst Cell "narrowband" exhaust gas oxygen sensors, which is what all cars come from the factory with, OBD2 usually involves an upstream and a downstream O2 sensor to get a more accurate picture.

It is important to note that the oxygen sensor is only looking for the amount of oxygen left after the burn of metered air. The problem with narrowbands though is there is often no correction for temperature.

But for a given fuel, AFRs @ Lambda .85v with EGTs of 400*C will be a far cry from Lambda .85v at 800*C:


So it is not actually telling you your AFRs it is telling you how close to stoich the burn is. The AFRs are determined based on the chemical equation going on in the combustion chamber, and since we often run rich under conditions where we are looking for performance like at >50% throttle input, this is why people have to switch to a "Wideband" oxygen sensor like the ones Bosch and Denso sell (that comes with a controller/gauge that corrects for temperature and provides a 5 volt loggable output) through groups like Innovative or AEM.

These are still nernst cells which basically create voltage through oxidation of the sensor's element, but they have thermistors and a logic to account for temperature.

So the stock sensors are usually best for when we are rich but approaching stoich or leaner than stoich stoich, and this is why they are good for finding fuel economy, but sometimes not so good for when you feel like spirited driving.

This is when good fuel comes into play for all of us.

Because it does two things.. first it gives you a bit of a buffer zone to work with because it is more knock resistant so you can maintain good LT and STs while also running leaner because it protects you from excess heat in the combustion chamber and radiated energy from the heat soaked intake tract which make you more knock prone on lower octane gas. So it is all around insurance for performance and allows the ECU to run as aggressive as possible under all conditions.

Lambda 1.0V is stoich for all fuels

So for example:

Lambda 1.0v is 14.7:1AFR for Pure Gasoline.

Lambda 1.0v is 14.2:1AFR for Gasoline with 10% Ethanol.

Lambda 1.0v is 9.8:1AFR for E85

All these will further affect your fuel trims because of the different fuel masses required for a given unit mass of air.

Hope that and this part of SB's post help clear it up:

So basically you want to keep your LTs as close to zero as possible by manipulating the STs with the gas pedal.

This combined with the above should help show you the difference in fuel trims you will experience between different grades and types of fuels.

But 87oct v. 93 should be relatively similar in terms of stoich. But since stoich is too lean for many cells on the various tables the ECU uses, the better fuel lets you run leaner and use less fuel in most instances.

This is why performance and efficiency typically increase with gasoline blends that have a high octane component.

This effect is more profound when there is no ethanol in the gas being used.

Hope that helps! As time goes by post up what you find with your Scan Gauge. Your info provides valuable data points, and we need as many as we can get to make a more accurate picture of what these ECUs do in different situations and climates. Especially on different fuels with different driving styles.

 

I though the GE8 has semi wide band o2s. The fuel trims is based off the MAF then the o2 or both?

I reread my links and the second one explained it better. My mpg is around 30 and going to try mid grade next tank to see where the fuel trims go. I figure it will go to 1-2 percent above 0.

 

No mention of timing here. Mixtures (fuel trim?) are going to vary on amount of gasoline vs alcohol in the fuel. A higher Antiknock Index (octane) is going to make a difference only if the ECU is capable of advancing the timing above the 87 AKI norms. Some owners manuals recommend 91 AKI for "maximum performance", most, such as our Fit, do not.

 

Typically running premium adds 2 degrees more timing and no knock retard. The ecu is more than capable to adjust for different fuel, add cold air kit, cat back exhaust and maybe header. The point to this is to show that the ecu adjusts. The owner manual says 87 or higher and can run up to 100 ron fuels with no problem. The timing in my car runs MBT Knock control tables

This applies to all high compression motors even though it from a Toyota website http://www.autoshop101.com/forms/h59.pdf

 

Timing and Fuel Trims are not directly related. The ECU has 50* of advance at its disposal, so it can certainly take advantage of better fuel.
Also, upthread I covered the basic differences in Lambda/AFRs for gasoline vs. alcohol.

If you would like to talk about Methanol or different target lambdas between different fuels or blends and different operating conditions we can do that as well.

I even have timing figures taken with an OBD2 datalogger from select points in the last three years from my constant experiments with fuels on my cars, I can gather those notes and compile them. I provided some recently in a discussion on spark plugs with another tuner.

Scratch & Dent is currently doing some interesting stuff with ethanol blends as well, perhaps he will chime in with his experiences. Silver Bullet, Klasse Act and Texas Coyote to name a few are also quite well versed in how the ECU reacts to different fuels and conditions.

There are several other scan tool owners on these boards, including the OP now, so we can all share actual advance numbers with you if you are curious.

If you would like to start a seperate thread on timing that would be cool and probably better than mucking up this one which I believe he wants to stick to Fuel Trims v. Fuel grades.

Or if you will take the time to read them... there are a few VERY thorough threads with multiple contributors that go into this far beyond what any average commuter needs to know..

And AKI is basically the same in the US as [(RON + MON)/2] method.

And your right, we do not have a recommendation for high performance, but we do have a stated minimum. And that is 87. I and others now have actual data on the differences between grades in addition to my experiences on many other platforms, those of other tuners as well as textbooks on the subject.

This is a debate that has been beat to death, resurrected and killed again, but I will start gathering links if you would like.

One big mistake a lot of very intelligent people tend to make is that they assume that you have to see actual pinging, knock or premature detonation in order for the ECU to pull timing.

But again that is a lengthy discussion for another thread perhaps.

 

KC and I wanted to show what the ecu is doing. We both have an Ultra Gauge and seen a difference in fuel trims. Like Texas Coyote said it can run on regular but the ecu is set up to run higher octane. First in KC post adding over 10 percent more fuel is not good. The car is running lean using the factory maps and that can causes knock and lower mpg. The closer you are to 0 the better. If the ecu was set up for regular it would be around 0 and even with ethanol it would go up to 2-3 percent more fuel. I was surprised that my fuel trims were pulling fuel out instead of adding because winter gas is less dense and expected 10 percent added fuel too. The point is the ecu can adjust over a wide variety of fuels and conditions. I am looking forward to KC adding premium and see where the fuel trims go. If the fuel trims continue to go positive then he found a problem with the ecu maps that needs correction.


Here is more tech FUEL TRIM(MING) DIAGNOSTIC TIME | Motor | Find Articles at BNET ,http://www.gadgetonline.com/U-Tune.pdf ,OBD2Scanners.com Volumetric Efficiency

 

DSM is correct in that I would like to focus on fuel trim vs fuel grade.
I'm saying this for a few reasons.
First off I would like to keep the variables down and stay in a real world on-the-road condition in a stock set-up.

Once we get fuel trim understood then it's time to move on to timing and other over-all factors.
-----------------------------------------
Expanding on my original understanding of Fuel Trim:

I'm comfortable in understanding that fuel trim numbers are directly affected by driving style in that engine load and throttle position and coolant temp contribute to their calculation.

I also understand the the primary O2 is used as well.
This is the only fuel trim calculation input that is 'combustion' related.

Here's my premise.
Running premium fuel will alter the output of the primary O2 sensor, thus effecting the fuel trim numbers.
In what I'm seeing that effect would be to bring them closer to either side of zero.
If this is so, then it might be safe to deduct that the base fuel trim diver map was set up for an octane other than the minimum recommended by Honda for the Fit.

It's as simple as that.

All the book learning needs to give way, at some point in time, to real world collection of data and the experience of speculation. K_C

 

All Fits have a Wideband (Air\Fuel Ratio Sensor in Toyota terms! LAF Sensor to some other...) from factory according to Bosch's website!

GD3 -> http://www.boschautoparts.com/Vehicl...=OxygenSensors
GE8 -> Don't have a part number Yet but a allready found the info on NTK's Website!

Marko!!

 

I thought so how else would the ecu know how far away the fuel trims are. Thank you the clarification DOHCtor. I know all the ecu's are similar and have adaptive learning.

 

Silver - good article, I found the original pdf w/ illustrations.

http://www.motor.com/magazine/pdfs/092006_11.pdf

 

This is exactly what should happen were things done under control conditions, and in theory is what should happen in at least the majority of cases.

So your working hypothesis and understanding is right on the money

Edit: Do you know if the 87 your are using currently has any ethanol in it? Or if the premium you intend to switch to contains any? This could skew your results.

 

Good find! That would allow for the ECU to be far more flexible and accurate!

It probably explains why the GE ECU is so good at dialing back gains when bolt on parts are added that increase VE and no outside changes are made to the tune.

Between the MAF and the Wideband it knows exactly how much air is entering and leaving under all conditions.

 

Fuel around these parts is 10% ethanol - so my fuel trims show that on 87octane fuel.
I was thinking to go to non-ethanol fuel, which I might be able to find, but it's scarcity and my tendency to travel north tells me to simply go with high test starting next tank full and watch the numbers.

When dealing with the objective the scientific process is at least worth striving for... though difficult to maintain in real world conditions.
But I figure that's where we all tend to live - or at least exist - so why not experiment there. lol

Silver convinced me to do this once before, but I really was driving by the seat of my pants and could feel no difference.
Well I've gotten new pants and a trick little dealybop to show me the numbers so my confidence is up.

Amazing how this quest has advanced, eh Silver?

 

I thought if the ecu was programmed for 87 and 10 percent ethanol would adjust the fuel trims 3-4 percent more fuel. 7-9 surprised me with them still going up. The -3.1 LT and ST still pulling fuel surprised me too. Even though its ethanol free it still has extra oxygen added because its RFG. The mpg factors are numerous so driving style has a lot to do with it but premium seems to make it easier to get good mpg. Try ethanol free regular and I bet the trims still add fuel but in the 5-6 LT percent range.

Just a quick note about timing, seen on wifes car not a real difference but thats due to the cold but the fuel usage was high averaging 26-28 mpg using regular.

I will use mid grade next fill up later today and report back, The ecu does adjust the trims pretty fast and seen that during the week. -3.1 on the way to work and bitter cold on the way home brought the long term fuel trims down to 0 but the ST still pulling -1.6 percent.

It going really good and if others post their numbers it will give a better idea whats going on.

 

It got up to 50 today and I went to get gas and the LT fuel trims went to -8. I filled up with mid grade and the fuel trims are still pulling fuel. The LT fuel trim -9.6 but I see the ST starting to add fuel. Tomorrow I will see where it goes on the highway. I am a little confused that they are still pulling fuel LT. I guess thats because the timing has not changed yet. I got 31.2 last tank and with the snow and extreme cold I think that good.

KC check the set up again.

 

I'm confident the UG is set-up correctly. I'm wondering about the trim numbers I'm seeing as well.

Today it hit a pleasant 55F in these parts. I saw long and short trims even out at 9.84 on an extended 70MPH cruise.

Seems this is where my FIT feeds.... avg 39MPG by the OBC.

Any feedback anyone?

 

My fuel trims leveled off at -3.1 LT and ST -2.3 to -5.5. The faster I drove it did get closer to 0 LT but the ST was alway pulling fuel. 2/3 89 and 1/3 premium 93 and approx. octane is now 90.5 which is close to 95 octane in Japan. I think the octane the maps are made from is 89 octane. I also think BP midgrade is ethanol free too. Its gonna warm up and expect the trims to continue to pull more fuel. Power is down because it down shifts to accelerate when before it would just go.

 

With 100 octane fuel the fit will give you 25 degrees of advance. My general understanding of the ecu has taught me that under wide open throttle the ecu will keep tying to advance as high as it can go and retard for knock as it occurs. The target I got with premium on n/a was 22.5 degrees before tdc. There is a huge huge power difference when you get up there. Octane on it's own never cause my ltft to change but it's amazing how much fuel quality varies from station when you are on the borderline of knock.