Engine Management Systems
- The manufacturer usually makes a lot of
compromises when mapping the EMU.
- Most production maps can be adjusted to give
more power with better fuel efficiency.
- The engine management system should be updated
every time a change is made.
- Even simple induction and exhaust changes should
be accompanied by a fuel and ignition map change.
Engine Management Unit (EMU) controls all the engine systems in a modern car.
The two primary systems being controlled are the fuel injection system and the
ignition system. Almost all other electrical systems are also controlled
directly or indirectly via smaller ECUs by the main EMU.
EMU uses fuel and ignition maps to control the engine at all loads and RPM
levels. The AFR and the ignition advance are controlled in this way.
elements in the successful installation and mapping of an EMU are a
comprehensive understanding of the engines varying fuel delivery and ignition
requirements over a broad range of operating conditions and study of the
factors influencing the engine’s fuel and spark needs measured and interpreted
by the control systems.
A thorough understanding
of the electronic systems affected by the EMU and of the electronic systems
onboard the EMU itself and a good knowledge of software development is also
essential… these latter two areas are the most neglected or lacking in most
Air-Fuel Ratio. The engine
has basic demands for air and fuel. The air-fuel mix can be manipulated to
improve driveability, increase economy and horsepower and control the
function of the fuel delivery system is to mix the air and fuel in the correct
ratios dictated by the EMU. Small variations in AFR can have a dramatic effect
on power and economy.
mixture is one with a lower AFR. There is insufficient oxygen to support
complete combustion of the fuel. Rich mixtures increase fuel consumption and
emissions of hydrocarbons and carbon monoxide. They tend to reduce power,
increase carbon deposits and foul spark plugs and dilute the engine oil.
mixture is the opposite. A larger AFR with more air than is necessary for
complete combustion. The fuel will burn more slowly and at a higher combustion
temperature. Lean mixtures reduce power, elevate engine temperatures and
increase emissions of oxides of nitrogen. It also causes driveability problems
and can lead to engine destruction.
Stoichiometric Ratio. This is
the ratio of the air to the fuel. Different ratios are suitable for different
engines, conditions and applications. For a modern engine the AFR must be
controlled very carefully and accurately. The best mixture for the most
complete combustion and the best compromise between lean and rich mixtures is
often the wrong mixture to use on forced induced and tuned NA engines.
stoichiometric ratio can also be represented as lambda. One Lambda equals a
ratio of 14.7:1 air to fuel.
Control for Power, Economy, Emissions. Power is
always a concern, but so too is the demand for good fuel economy and reduced
perfectly mapped system, adjusting the system for maximum power will mean
increasing fuel consumption. Minimizing fuel consumption means sacrificing
power and driveability. Both max power and max fuel efficiency means increased
good mapper can deliver good power, quick starting and smooth trouble free
driving without sacrificed fuel efficiency.
production maps can be adjusted to give more power with better fuel
Ignition Timing. In terms
of all four major aspects of performance – power, fuel economy, emissions and
driveability – ignition control is equally as important as the air-fuel mix.
Combustion in the cylinders takes a certain amount of time. Simultaneous
control of the fuel and ignition is essential to engine tuning.
start, the best ignition timing is near TDC(top dead centre). More advanced
timing allows the engine to fire while the piston is still rising. If the
engine is hot, retarded ignition timing can prevent reverse torque and starter
damage. It is desirable to retard ignition timing for low cranking speed
conditions and more advanced ignition is permissible under less challenging
starting, the ignition timing can be advanced to improve the engine running
and to reduce the requirement for enrichment. After this ignition retard can
be used to quickly heat the lambda sensor and cat. Advancing the timing during
warm-up under part throttle will improve power and driveability and fuel
the throttle very quickly places demands on the engine. The sudden transition
from closed throttle to fully open throttle raises the manifold pressure and
additional fuel is required, but this fuel is not instantly available. There
is a lag between the ideal and actual delivery of fuel.
smooth throttle responses the basic air and fuel sensing is too slow. The fuel
system must be able to compensate for rapid increases in manifold pressure.
Acceleration enrichment is used to provide the required throttle response and
the tuner must set up the parameters in the EMU to achieve this…. Some basic
EMUs do this automatically.
systems a separate acceleration enrichment table must be programmed to achieve
this and a competition table will be very different to a standard road table.
Basics of High Performance Mapping.
book could be written on this topic alone, but as a general guide keep the
following in mind….
mods to the engine to increase power, revolve around improving the volumetric
efficiency of the engine so that more air can flow into the cylinders on each
stroke… most of the other links on this website relate to this in one way or
another. The gains may be tailored to the middle or top end of the power band.
Higher lift and longer duration cams, larger valves, ported heads, better
intake manifolds and exhaust headers, free flowing exhausts and induction
systems all do the same basic job.. improve air flow. And of course forced
induction forces more oxygen into the cylinders.
system must compensate for this increase in air. The standard EMU and fuel and
ignition setup is designed to be optimum at the standard air flow and when we
increase the air flow we can quickly go outside of the stock EMUs most
efficient range of operation and when we go to more extreme states of tune we
can go completely outside of the stock EMUs range of operation.
modification made to the engine, a remap of the air-fuel and ideally of the
ignition is necessary to gain the full value of the changes. A few horsepower
may be liberated without remapping, but to get any significant performance
increase, a remap is required.
Stoichiometric mixture setting (or the Lambda
setting) on all production cars are not optimized for peak power, so a remap
without changing anything else on the car will immediately liberate some
power. Peak power is achieved with a slightly richer mixture in some areas of
the power band and a leaner mixture in other places. There are some exceptions (such as the Subaru Impreza), but in general, we can
achieve more power AND better fuel economy than the production EMU… this is
especially true on hot hatches and almost all NA cars(the downside is slightly
higher emissions, but still well within the NCT limits). Even cars with very
aggressive full throttle tables can be significantly improved.
Conservative fuel control is usually accompanied by conservative ignition
mapping… mainly because most manufacturers have to limit themselves to
operating on 91octane fuel. The revised fuel control mentioned above can be
further enhanced by better ignition mapping, tailored specifically for the
fuel you are running on(normally 95 octane).
adjust the stock EMU without using a replacement or piggyback unit will at the
very best produce a purely linear response in fuel and ignition change. You
can tune one point in the power curve for best power, but the rest of the
power curve will suffer. Resulting in a big drop in overall power. The net
result is that even the area you tuned will show less power because the
surrounding load sites will be operating at reduced power and the added
theoretical power of the site you tuned won’t have enough shove to overcome
the reduced power of the points immediately before and after this point. We
know every trick in the book when it comes to tweaking stock EMUs and the best
that can be achieved is a perceived increase in power, but on inspection on
the dyno, you end up with a slower car. These tweaks include upping or
lowering the fuel pressure, altering the mass air flow sensor or the throttle
sensor or the manifold absolute pressure sensor etc.. all these changes
produce a LINEAR change in air-fuel mix that isn’t of real practical value. On
the ignition side, you can rotate the crank angle sensor, or modify other
sensors such as the ref or trigger sensors and in this way achieve a linear
change in ignition advance or retard. The difference here is that you run the
risk of detonation and pre-ignition which will lead to head gasket failure is
you’re lucky and piston meltdown on a worst case scenario.
the only way to properly remap is to use a fully mappable replacement EMU or
to use a good piggyback EMU.
exception to this is the boost pressure on turbo and blown cars. Upping the
boost a little by altering the wastegate in some way (electronically or mechanically), will normally give a nice power increase
across the entire charged power curve – without any change to the EMU.
Obviously no gains are available in the off boost area. However, care must be
taken to keep within safe limits. Once you go past a certain limit (different on each car) you can say goodbye to your head
gasket or at worst suffer complete engine failure. A good example is the
Celica GT4. The factory boost level is 0.7bar(depending on year), and on 95
octane the engine will happily run at 0.9bar, but much past this, without any
other mods to exhaust or induction is not advisable. Competition engines can
run at 1.3bar on 97 octane, but a revised head gasket is advised.
changing the induction and exhaust will usually up the boost without going
near the wastegate or the EMU(e.g. Skyline GTR). Always monitor the boost
levels after every change to the engine, even if the change isn’t intended to
modify the boost level.
just because the engine appears to run OK after a boost change doesn’t mean
that you aren’t doing permanent long-term damage. Any change should be carried
out on the dyno with all the diagnostic and knock – det sensors attached. Then
engine should then be run at full power for a sustained period and all
parameters carefully monitored.