- In our last lesson, we looked at the basics of reflashing.
We found out what reflashing was,
and we found out why we might want
to make tuning changes to our car in the first place.
Now you'll remember that the two fundamental aspects
of tuning that we discussed last time
where fuel and ignition tuning.
In this next lesson, we're going to discuss
the fuel tuning in a little more detail,
and we'll also have a look at an example
of how we can make changes to the fuel delivery
using the HP Tuners reflashing package
on this 2013 ZL1 Camaro fitted
with a 6.2 Litre Supercharged LSA engine.
Before we get stuck into this though
let's have a quick look at the HP Tuners scanner
and we'll find out what's going on here
as this is going to make a big difference
to what we need to make changes to
in our editors software.
Right now we've got our engine sitting at idle
and you can see that our engine RPM
is sitting at about 580 RPM.
If we look over to the left we can see
our engine coolant temperature
and intake air temperature.
Our engine coolant temperature's at 95 degrees centigrade
and our intake air temperature is at 25 degrees centigrade.
What we're interested in mainly
for this particular lesson is our fuel delivery
and there's a couple of things we need to look at here.
If we move down our graphs we can see
that we have two parameters here,
one is labelled equivalence ratio commanded
and this is our commanded or requested air-fuel ratio.
In this case, we're using units of Lambda,
but this is what the ECU is asking for
in terms of air-fuel ratio.
So right now, at idle, you can see
it's requesting Lambda one,
which is the same as Stoichiometric of 14.7 to one
in terms of air-fuel ratio values.
And the pink values below that
you can see our Measured Equivalence Ratio
or Lambda value and you can see that
that's sitting right on our target right now,
well, it's moving very slowly backwards and forwards,
but we're sitting right on our target.
Now, the way this is being achieved at the moment
in idle, is because the engine is operating in closed loop.
And we can see some of the parameters associated
with our closed-loop control right here.
These are labelled LTFT for Long Term Fuel Trim
and STFT for Short Term Fuel Trim.
So essentially what's happening here
is that the ECU is taking feedback
from the oxygen sensors in the exhaust.
These oxygen sensors tell the ECU
that the engine is richer or leaner than Stoichiometric
and then the ECU can make adjustments
to the fuel delivery in order
to achieve the target air-fuel ratio of Lambda 1.0.
So we can see that at the moment
our trims are all sitting very close to zero
and this is also indicative of a good tune.
If our trims are very positive or very negative
it means that the ECU is doing a lot of work
in order to correct errors in the measured air-fuel ratio.
Okay, so now we know what's going with our scanner,
let's talk about how the ECU knows
how much fuel to deliver in the first place.
And this is a common aspect with factory ECU,
particularly late-model ones, we're going to find
that most of these ECUs are fitted
with air flow metres or Mass Air Flow metres, MAF for short.
These Mass Air Flow Sensors are great
because they tell the ECU exactly
what mass of air is entering the engine.
Now, the reason why this is important
is because when we're talking about fuel delivery
we're talking about a ratio of fuel to air.
More specifically, we're actually talking about
a ratio mass of fuel to mass of air.
Once the ECU knows what mass of air
is entering the engine, it still needs
a little bit more information.
What it needs to know is what mass of fuel
the injectors are able to supply.
Let's jump back into our VCM editor software
and we can see where this data come from
and the tables inside the ECU.
Here, I'm under Fuel General table
and you can see that we have a lot
of parameters relating to injector controls.
I'm not going to go through all of them here,
but in particular you can see that we have
some tables relating to injector flow rate.
The main one here that I'm going
to just look at briefly is our
flow rate versus pressure.
And if I open this, we can see
we get a two dimensional table
with Pressure Delta on the X-axis
and the values in this table define
what mass of fuel in Grammes Per Second
can be supplied by the injectors
at varying differential fuel pressures.
Okay, so now, the PCM knows both
what mass of air is entering the engine,
and what mass of fuel the injectors are able to supply.
If it knows all of this information,
it's actually quite easy for the ECU
to decide how long to hold the injector open for
in order to achieve our desired target air-fuel ratio.
Let's move back to our scanner for a moment
and again let's look at our long term
and short term fuel trims.
I like to think of these parameters
as an indication of the health of our tune.
When we're seeing these numbers
all sitting very close to zero
it means that the information that
the ECU is receiving from the Mass Air Flow Sensor
as well the injector calibration data is all accurate.
If these two pieces of information are both correct
it's very easy for the ECU to supply the correct of fuel.
So we've got our engine operating now at idle,
as we've mentioned, and we know
that our target air-fuel ratio
is Stiochiometric Lambda 1.0 or 14.7 to one.
You'll remember that in the last lesson
we looked at the Power Enrichment Table
in the GM software.
Now, this Power Enrichment Table
which we can see here remember was
a two dimensional table which defined
our target air-fuel ratio when
the engine was in power enrichment or in other words,
an open loop or wide open throttle.
So instead of supplying a full
three-dimensional table of our air-fuel ratio targets,
GM instead have decided to just simply define
whether the engine is operating in closed loop mode,
in which case the air-fuel ratio target
is always Stoichiometric, or alternatively
if it's in Power Enrichment Mode
in which case our air-fuel ratio targets
come from our Power Enrichment Target Table.
So when we're trying to alter our fuel delivery
in the GM ECU, we're going to be spending
most of our time on the Power Enrichment Table.
When we're talking about the GM
Power Enrichment Table though,
what exactly do these numbers mean?
Most tuners wouldn't be familiar
with the term Equivalence Ratio
which is how GM are defining the target air-fuel ratio
so let's look at these numbers now.
In the table for example, we can see that
above 5,000 RPM, the Equivalence Ratio target is 1.316.
Now on it's own, that might now mean too much,
so let's find out how we can convert
into meaningful numbers.
What I'm going to do is bring up
my calculator so we can actually calculate
the air-fuel ratio as well as the Lambda.
The easiest way is to convert between
Equivalence Ratio and Lambda,
is they're simply the inverse of each other.
What this mean is if I insert the Equivalence Ratio target,
1.316, and then I use the inverse function
on my calculator, we're going to see
what this equates to, in terms of Lambda values.
Let's do that now.
And we can see that this equates to 0.759,
or let's call it 0.76 Lambda.
So this gives us a more useful value.
Now if we want to convert that into
air-fuel ratio values, we can simply multiply
by the Stoichiometric AFR in this case for pump gas,
let's call that 14.7-to-one,
so let's go through that process now.
So we'll multiply by 14.7 and we can see
that our target and air-fuel ratio values
is 11.17.
So this is how we can use the Equivalence Ratio Table
and convert the numbers into what most tuners
would be a little more familiar with understanding.
Now if you don't wanna go through
the process of converting to Lambda first,
we can convert straight from Equivalence Ratio
into Power Enrichment values, and vice versa.
Let's how we can do that.
For a start, if we enter our Stoichiometric
air-fuel ratio, again, 14.7-to-one,
and we now divide by the Power Enrichment value,
in this case 1.316, we're going to be able
to convert to our commanded air-fuel ratio.
So you can see that gives us exactly the same result.
So Stoichiometric AFR divided by our
Power Enrichment gives us our target air-fuel ratio.
If we want to convert straight
from a desired air-fuel ratio target
into Power Enrichment numbers,
we can do that really easily too,
in this case, we simply divide
our Stoichiometric AFR by our desired target air-fuel ratio.
Let's do that now.
So we take our Stoichiometric value, 14.7,
and we divide that by our desired target,
in this case 11.17, press enter,
and we can see we have our Equivalence Ratio
target value, 1.316.
So hopefully this explains what
the Equivalence Ratio values mean
in our Power Enrichment table.
Now we're gonna make some changes
to this table and see the effects on our tune.
We're going to start though by laying down a base run
with this air-fuel target table or Power Enrichment table.
Let's do that now.
Okay, we've got our run complete
and on the dyno we can see that we made
362 kilowatts or 486 horsepower at the rear wheels.
What we're looking at here is our redline
which is Lambda value that's being measured
by the wide band Lambda sensor in the exhaust.
And we can see that at the start of our run
we're sitting at around about 0.8, 0.82 Lamba,
and at the end of the run we're sitting
at around about 0.76.
Lets jump into our VCM sanner software though
so we can see it in a little more detail.
Now here we can see first of all in the top
we've got our run here, and you can see that
at the start of the run, we're sitting
at around about 1500 RPM and we went through to 6000 RPM.
So this is essentially a repeat of
what we saw in our first lesson.
What we're interested in though
for this particular lesson is our
Equivalence Ratio commanded versus our measured Lambda.
So we can see here our green value
is our commanded lambda value.
At the start of the run, you can see that
our commanded Lambda value before
we go to full throttle is sitting at 1.0.
You can also see at the same time
that our short term, long term
fuel trims are still active.
So this means that the ECU is still
operating in closed loop.
We haven't gone to a high enough
throttle setting to move into Power Enrichment.
At this particular point here you can see
that our commanded Lambda value drops to 0.80,
so this when the ECU moves into Power Enrichment
and this corresponds to the point
where I've started to move throttle wide open.
We actually transition into Power Enrichment
at 47 per cent throttle opening at 1700 RPM.
Now once we've gone to wide open throttle
and start the run we can see that
our Equivalence Ratio commanded,
or our commanded air-fuel ratio value
and our measured match very closely.
Particularly in the top of the run,
you can see that the two values are exactly the same.
And again this is a sign of a well-tuned ECU.
If our measured air-fuel ratio matches our commanded,
what this means is that the ECU knows
the correct amount of air that's entering the engine,
and it can supply the correct amount of fuel.
If on the other hand we're seeing errors
that are significant here, so our measured air-fuel ratio
wasn't matching our target, this means
that there's problems in our calibration
and we need to do some work there.
Okay, so now we've seen our base run,
what we're gonna do is make a change
to our air-fuel ratio target.
So let's go back to our VCM editor software,
and for the purpose of this quick demonstration,
all I'm going to do is highlight the entire table
and what I'm going to do is multiply it by 1.05.
So essentially this is going to add 5 per cent more fuel.
It's going to richen our entire mixture.
So now what we're going to do is
we're going to just shut the engine off
and we're going to flash that change
into the ECU, so we can run it again
and see the effect of that change.
In order to flash this change into the ECU,
all I need to do is click on
the little Write Vehicle icon here.
We can then select which of the two controllers
we're going to write to, in this case
I'm just choosing not to write to
the Transmission Control Module,
we're only making changes to the Engine Control Module,
so that's the only change I'm going to go through.
When click 'Write', the write process will continue,
and we'll reflash the ECU with these changes.
Depending on the ECU you're tuning
this can take anything from a few seconds,
up to several minutes.
In our case we're looking at around about 45 seconds.
So we'll just allow this process to complete now.
Right, with our reflash complete,
we've got our engine up and running again,
so let's get into fourth gear,
perform another pull on the dyno
and see the effect of that change
we've just made to our fueling.
Okay, that's our second run complete
and you can see this time we've made
a little bit less power.
We're at 344 kilowatts or 461 horsepower at the rear wheels.
Now, part of the reason for this
is we have purposely moved to quite a rich air-fuel ratio.
And while the power that an engine produces
is relatively stable, I've a reasonable range
of air-fuel ratios.
Now if move excessively rich or excessively lean
from that point we will start to see the power drop off.
The important part here though
is to look at our air-fuel ratio.
Now remember we made a five per cent change
to that Power Enrichment table.
The blue line which we can see
on the dyno here is our air-fuel ratio
Lambda plot from our first baseline run,
and now we can see the redline from our current run.
So particularly in the top end here
we can see that our air-fuel ratio Lambda
is sitting at around about 0.72,
and that's obviously richer than our first run.
Let's jump into our scanner
and we'll have a better look at this.
Now the part that we're really interested in here
is to compare our commanded Lambda with our measured Lambda.
And again you can see that our purple-pink line
of our measured Lambda value overlays
almost exactly with commanded Lambda.
We're seeing errors very, very close to zero,
we're always within about 1 per cent
of our commanded air-fuel ratio value or Lambda value.
So this is just a brief demonstration
showing you how quickly we can
make accurate changes to the air-fuel ratio
our engine's running, using reflashing.
Now all of this does rely on the Mass Air Flow Sensor
calibration being correct.
In other words, it's essential
that the ECU correctly knows how much air
is entering the engine.
If it doesn't know this correctly,
then it can't hope to give us
the air-fuel ratio that we're asking for.
Now the really important part of all this is
when we're reflashing a factory ECU
often our job is really, really quick and easy
because we're only really focusing on
the open loop area of operation that wide-open throttle area
of operation that we've just looked at.
Under cruise and under idle,
where particularly a street car is going
to spend the majority of it's time,
we can simply allow the closed-loop control system
to take care of any small errors,
and that let's us simply focus on
the wide-open throttle operation.
This is much quicker and much easier
in comparison to the likes of a stand-alone,
aftermarket ECU, where we have to map
the entire fuel table in three-dimensions,
looking at all of the combinations
of load and RPM.
Now if we're tuning an engine that's seen
significant modifications such as
the addition of a supercharger or turbo,
or perhaps the fitment of a larger camshaft,
then our fuel-delivery tuning is going to require
a little bit more work than what we've just looked at.
For probably 90 per cent of reflash tasks though,
we're going to be able to concentrate
our fuel-tuning solely on the open-loop area of operation.
So now we can move on and in our next lesson
we're going to be talking about ignition timing
and we'll see how we can adjust
the ignition timing by reflashing the ECU.
Look out for the next lesson in your email inbox shortly.