engine menagment.pdf

fast tech / TECH / ENGINE MANAGEMENT /

fast tech

Here we are with the third

and ﬁ nal part of Stu’s engine

management tutorial.

little in parts

one and two, and that you now

have a working understanding

of what makes the engine

management system tick, and how

each separate item plays its role in

the whole package.

We’ve previously discussed the

sensors, how they work and what

they feed out (issue 247).

We have also discussed the

ECU, what inputs it reads and

what hardware it actually drives

as well as how the two basic

conﬁ gurations differ (Speed

Density and Mass Air Flow,

covered in issue 248), so

what’s the missing link?

Well, here in part three

we will discuss the

engine management’s

control program —

or the map or chip

as many of you

will know it.

OUTPUT

CONTROL BRIDGE

The ECU has various inputs

from water, air, pressure and

speed sensors to name just

a few. It also has its outputs

such as idle valves, injectors

and boost control valves. But

how does it decide what to do

with its outputs?

Every ECU will have an engine

control map programmed

within it that allows it to operate

its outputs with reasonable

intelligence using a system of

logical control parameters.

Let’s look into this subject in

a little more detail.

Words: Stewart Sanderson

CONTR OL

covered in issue 248), so

what’s the missing link?

Well, here in part three

we will discuss the

engine management’s

control program —

or the map or chip

as many of you

will know it.

a little more detail.

CENTRE

0114

DECEMBER 2006 FAST FORD

FAST FORD JANUARY 2007

0115

fast tech

I HOPE you learnt a

P A RT 3 : T H E MA P

FAST FORD JANUARY 2007

0115

fast tech

/ TECH / ENGINE MANAGEMENT /

fast tech

speed sensor can create havoc

with your fuelling and spark

advance maps.

actually carries more oxygen at this

temperature than air at 40 degrees

C did when the base fuel map was

made, and thus it requires more

fuel adding to it to keep the air fuel

ratio correct in the combustion

chamber. Again, it normally has a

side map almost identical to the

water temperature one that simply

adds and subtracts from the base

fuel map to keep the mixture

correct for all air temperatures.

Typically it will be mapped from

-55 C to +125 C.

Due to this air density

change, the spark advance

requirement also changes

with the temperature of

the air, cooler air requiring

a different advance ﬁ gure

than hot air to generate

peak cylinder pressure at

the same point. Naturally,

this map being accessed

incorrectly could either retard

the engine and lose lots of power,

or over-advance the engine and

destroy

it completely.

actually carries more oxygen at this

temperature than air at 40 degrees

C did when the base fuel map was

made, and thus it requires more

fuel adding to it to keep the air fuel

ratio correct in the combustion

chamber. Again, it normally has a

side map almost identical to the

water temperature one that simply

adds and subtracts from the base

fuel map to keep the mixture

correct for all air temperatures.

Typically it will be mapped from

WATER TEMPERATURE

MULTIPLIER

One of the biggest variables on

a modern engine is its actual

temperature. This is measured

on almost every engine by the

simple water temperature sensor

screwed into the cylinder head or

surrounding areas.

I should mention in case you

don’t know, that the colder an

engine actually is, the more fuel

it requires to make the same

power. So, when the engine is at -5

degrees C, it will require far more

fuel to idle than it will after it has

been running for 30 minutes and

the water is up at 90 degrees C.

So, how does the ECU actually

work out how much fuel to add

and when? Well, there will be a

map inside the ECU that graphs

the water temperature separately

in degrees and each reading (or

breakpoint as we call it) will have a

multiplier ﬁ gure for the fuel map.

In the example shown here

we have what is essentially the

following instruction. “If the water

temperature is 5 degrees C, multiply

the fuel map by 1.52 (adding some

52 per cent more fuel).”

So, if for argument’s sake our

base fuel map adds 1 millisecond

of fuel at idle speed with the

engine fully hot, the warm-up map

changes that to 1.52 milliseconds if

the water is at 5 degrees C. Typically

it will be fully mapped from -55 C

to +125 C.

The same situation is true for

spark advance; it has its own water

temperature-based multiplier map

that allows more advance on a

cold engine as this is what gives

best results. Once again, incorrect

application here can spell death,

too. Do you see how this system

works? Good, onto air...

incorrectly could either retard

the engine and lose lots of power,

or over-advance the engine and

and discover the injector

nozzle now takes 0.4 ms

to open and 0.4 ms to

close. This means we now only

have 0.2 ms to inject fuel, which

we have already established is not

enough, so the solution is? Yes,

you guessed it; we need to open

the injector for 1.4 ms if the batter

voltage is this low to account for

the dropped opening and closing

speed.

This is inﬁ nitely variable so

also has its own table, normally

spanning around 9-15 volts in very

small increments. Interestingly,

what do you think would happen to

a highly-tuned car when ﬂ at out on

the motorway and the alternator

starts to die due to your massive

high-power stereo draining it to

death? Yes, I have seen many

engine failures attributable to this.

Take care out there music lovers...

to open and 0.4 ms to

Top. The base fuel map.

Top to bottom is pressure,

left to right is engine speed

speed and load combination you

wish to throw at it mile after mile,

day after day.

MAP SENSORS AND

AIRFLOW METERS

In our example fuel map, can you

see the scale on the left? That scale

is essentially load. The scale itself

in this example is actually scaled in

volts, and it is zero to 4.9 volts out

of a MAP sensor. It would be similar

for an airﬂ ow meter. The more load

the engine is under, the higher up

that scale the fuel injector switch-

on time will be read from at any

given rpm — for example, full boost

and 5500 rpm will read a value of

230 from the map.

The ﬁ gure itself equates fuel

injector opening time into a decimal

number and is of little consequence

to this actual discussion, but to

oversimplify the system, let’s just

say it gives the ECU the ability to

vary the injector opening time

between fully closed and fully open.

In an old fashioned system

like a Cosworth you can have

anywhere from zero (closed) to 255

(always open), but more modern

systems can be 0-255000. So, as

you might expect, the 230 in that

table is running the injectors quite

hard indeed. Imagine what would

happen if the MAP sensor only

delivered 2.5 volts instead due to a

wiring issue, or the pipe leaked due

to a missing clip so it didn’t get the

same boost as the plenum... The

management computer would, of

course, deliver a totally incorrect

amount of fuel from totally the

wrong area of its fuel map.

When looking at the spark map,

the same is true, the more load

an engine is put under, the less

advance is normally required.

As many of you will know, too

much advance can spell death

to any petrol engine, so it is very

important that the correct ﬁ gures

are delivered to ensure good

performance and engine life.

BATTERY VOLTAGE

MULTIPLIER

You may be wondering what

battery voltage has got to do with

the fuel map. You would be forgiven

for not knowing as it’s not the

most obvious thing in the world. It

is extremely important and one of

the least-understood things in the

modifying business.

The injectors at 13.8 volts

operate at a certain speed, going

from closed to open, and from

open to closed. As the voltage

drops, the time taken to open and

close increases, and therefore, they

must be held open for a longer time

than in the normal fuel map due to

the fact the injector will have spent

more of its given allowance actually

opening and closing.

Let’s elaborate: if, for example,

we are at idle and the injector is

being told to open for 1 millisecond

(ms), it will actually spend about

0.2 ms of that time opening and

0.2 ms of that time closing, so

the fuel required to idle smoothly

is actually injected in 0.6 ms.

Understand that? OK, so now let’s

say we drop the battery voltage

down from its nominal 13.8 to 11

but most commonly you ﬁ nd that

the main fuel map is erred slightly

towards generating maximum

power and the wide open throttle

multiplier adds a little more to

keep a check of the exhaust gas

temperatures generated under

hard-use conditions.

It is also used to control

many transient fuel correction

parameters which take care of

unusual things like fuel hesitations

when you move the throttle from

one place to another, and other

very complex things related to

ﬂ uid dynamics that this article

just doesn’t have enough room

to deal with.

Again, given that extra fuel is

needed at wide open throttle, the

sensor failing to inform the ECU of

Bottom. Base spark advance

map. Again, top to bottom

is pressure, left to right is

engine speed

THE MULTIPLIER MAPS

The problem with the two base

maps described is this: they will

only ever be correct when the

engine is operating in the exact

same conditions that the map

was developed under. In most

cases this is with the intake air

at 40 degrees C, and the water

temperature in the engine block

at around 88 degrees C.

So what happens when these

parameters change? Morning,

noon and night, Spring, Summer,

Autumn and Winter? Yes, the

ﬁ gures you can see in the base

maps will be substantially

incorrect and the engine would

run badly, if at all.

To rectify this, there exists a

whole host of additional maps

that either add or subtract

values from the main base maps

depending on input data from

your multitude of sensors. This

is the way temperature and

additional external inﬂ uences

are dealt with in 90 per cent of

management systems. Please

read on for examples of how the

various multiplier maps inﬂ uence

the running of your engine under

different conditions.

THE BASIC FUEL-

INJECTION MAP

Every control map will have a base-

fuelling map. This map will have

been developed with the engine at

full normal operating temperature,

— likely on a dyno ﬁ rst of all — for

many 10s if not 100s of hours.

This ﬁ nalised fuel map will cover

all manner of throttle/load/speed

combinations and will run the

engine correctly whether idling at

850 rpm on your driveway or ﬂ at

out on the Autobahn with 15 lb of

boost pressure rushing into it at

8000 rpm.

ENGINE SPEED SENSOR

You see the scale on the top of our

example fuel base map? OK, as you

have likely guessed by now, that is

the scale used to determine how

much fuel is added to the engine at

different rotational speeds.

Due to the fact an engine’s

volumetric efﬁ ciency (VE) value

is different at virtually every

different rotating speed, the fuel

level injected into the cylinder at

low speed can be very different to

the requirements at high speed.

Conversely, as an engine’s speed

increases so does its advance

requirements, so it’s important that

the speed signal is correct to avoid

us over or under-advancing the

engine, especially as the former can

be deadly.

Hopefully, it is easy for you to see

how a malfunctioning crankshaft

THROTTLE POSITION

MULTIPLIER

Throttle position has various

multiplier maps connected to

it, the most common one being

injection at wide open throttle

(WOT). This map, as its name

suggests, actually alters the

amount of fuel injected when you

go to wide open throttle. It can be

mapped in many different ways,

Top. Fuel enrichment multi-

plier. More fuel is added when

cold, and gradually decreases

as engine warms up

AIR TEMPERATURE

MULTIPLIER

Arguably the second biggest

variable is the air temperature. This

is because air is actually denser

when it is cold than when it is hot.

For argument’s sake let’s pretend

our air is at 5 degrees C — it

Bottom. Wide Open Throttle

map. This is the map that

adds extra fuel when you

mash your foot to the ﬂ oor.

At 5500 rpm we have 1.24 x

the fuel listed in the base map

THE BASIC SPARK

ADVANCE MAP

Every control map will also have a

base spark advance map. As with

the fuel map, this will have been

developed over 100s of dyno and

road hours and real-life testing. It

will be suitable for pretty much any

0116 FEBRUARY 2007 FAST FORD

FAST FORD FEBRUARY 2007

0117

fast

fast tech

tech

actually carries more oxygen at this

temperature than air at 40 degrees

C did when the base fuel map was

made, and thus it requires more

fuel adding to it to keep the air fuel

ratio correct in the combustion

chamber. Again, it normally has a

side map almost identical to the

water temperature one that simply

adds and subtracts from the base

fuel map to keep the mixture

correct for all air temperatures.

Typically it will be mapped from

-55 C to +125 C.

Due to this air density

change, the spark advance

requirement also changes

with the temperature of

the air, cooler air requiring

a different advance ﬁ gure

than hot air to generate

peak cylinder pressure at

the same point. Naturally,

this map being accessed

incorrectly could either retard

the engine and lose lots of power,

or over-advance the engine and

destroy

it completely.

and discover the injector

nozzle now takes 0.4 ms

to open and 0.4 ms to

fast tech / TECH / ENGINE MANAGEMENT /

this position can be deadly, and one

reporting it too early can cause big

over fuelling problems.

off the mixture to compensate. How

much it does so varies according

to these Lambda correction

maps. Low load only requires low

correction and higher loads require

more drastic correction.

These correction maps are

essential to stop the ECU over

compensating and getting stuck

in a rich-lean loop it cannot

correct. When the Lambda sensor

input is faulty the ECU will try

to compensate based on the

information it is given, leading to a

too rich or too lean situation.

valve can lead to stalling of the

engine or too high an idle speed,

but conversely so can any sensor

error that causes the idle speed

map to drive the valve incorrectly,

such as a coolant sensor error

telling the idle map that the engine

is in fact hot when it is really cold.

Top. The idle speed control

map. This map shows how

the valve is told to open

more, the colder the engine

is, giving you the raised cold

idle speed

KNOCK SENSOR MAPS

The map attributable to the knock

sensor on most system is based

on load and rpm. When knock is

detected by the sensor it looks up

its load and speed position in the

table and retards the timing by the

amount dictated there or until the

knock stops.

The knock table is essentially

a table that dictates how severe

the retard is. This table exists as it

will require less retard to make the

engine safe at low rpm/low load

than it does at high rpm/high load.

Some more modern systems are

now fully active and constantly

advance or retard the ignition,

keeping the engine on the verge of

knock where maximum power can

always be found.

Obviously when the knock

sensor reports knock that doesn’t

exist we end up with a retarded and

non-responsive engine. Conversely,

when it fails to report knock that

is actually present we can end up

with an over-advanced or totally-

destroyed engine.

Bottom. The boost map. Top

to bottom is rpm, left to right

is load. This map controls

your boost control solenoid

and thus your boost curve

BOOST MAPS

The boost pressure on virtually all

production turbocharged engines

is controlled by a boost pressure

solenoid. This solenoid, as you will

no doubt have guessed is controlled

by its own map in the ECU.

This map (or more commonly

maps) can be controlled by a

multitude of things such as load,

engine speed, throttle position and

air temperature, not to mention

barometric pressure, gear selection

and road speed; either way, the

map works in a similar way to the

idle speed control valve, essentially

controlling a pulse width output

to the valve itself that in turn

controls how much air reaches the

wastegate actuator, or how much

air is bled away from it, depending

on whether the system is a bleed-

on or bleed-off design.

Faults with this valve normally

mean a lack of, or too much boost

pressure, and faulty sensors can

cause the pulse width delivered by

the ECU to be incorrect, such as an

air temperature sensor reporting

extremely hot air, or a knock sensor

reporting detonation. As you are no

doubt aware by now, everything is

very tightly interlinked.

Well, that about covers the basic

maps that we deal with everyday

as an ECU mapper, but there are

literally many 100s more maps in a

modern ECU — yes, 100s more.

You would probably be quite

shocked if I were to show you

every map in a modern ECU, but

sufﬁ ce to say that the ones I have

shown you are the mere basics

and don’t even scratch the

surface of a modern engine

control system.

But they are still the foundation

maps upon which all management

control programs are built.

IDLE SPEED

COMPENSATION MAPS

The idle speed control valve is

often a source of problems on

many old Fords.

This valve is controlled by a map

in the ECU, that essentially dictates

what pulse width is sent to the

valve. The pulse width at the valve

controls how much air is allowed

to ﬂ ow, and this controls the idle

speed directly. The map is normally

based primarily on temperature;

when the engine is cold the idle

speed needs to be higher to

maintain a stable idle speed, so

the ECU looks at the temperature

and takes the required pulse width

out of the map that will give the

correct idle speed.

Typically, as the engine warms

up the map delivers less and less

pulse width to the point the valve

has no effect at all. Some systems

also work the valve in other

situations such as when heavy

loads are applied to an engine that

may stall it, such as air conditioning

activation at idle. Naturally, a faulty

CONTACT

Stewart Sanderson

co-owns Motorsport

Developments in Blackpool

01253 508400

www.remapping.co.uk

LAMBDA

CORRECTION MAPS

Since 1992 pretty much all engine

management systems in the

world are operated in closed-loop

mode with the help of a Lambda

sensor. The output of the Lambda is

monitored and when fuelling is not

at the chemical correct ratio of 14.7

parts air to 1 part fuel — the ECU

automatically richens up or leans

NEXT MONTH

Cylinder heads: how valve

and port sizes affect power,

plus how much difference

can they really make?

0118 FEBRUARY 2007 FAST FORD

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: