A Basic Guide to Electronic Fuel Injection
for Minis
Disclaimer:
This article is intended as a basic guide to
converting a Mini to EFI only. It's sole purpose is to provide basic information
about EFI conversions. Seek professional advice before considering converting
your vehicle to EFI. If you have any comments, suggestions or questions about
this article, whether you liked it or not or if you'd like to see more articles
on EFI, email me at the above address or see me at a club meeting.
Converting your Mini to Electronic Fuel Injection (EFI) has its
advantages as well as its disadvantages.
Advantages:
If done properly, converting your Mini to EFI can
have many benefits. The EFI Engine Control Unit (ECU) can control all aspects of
the combustion of the air/fuel ratio under all conditions. For each and every
load point throughout the rev range that the engine may experience, the EFI ECU
can calculate the optimum timing and delivery of fuel as well as precisely when
ignition will take place by supplying spark at exactly the right time in order
to maximise power and torque. This results in an infinitely more flexible engine
with wider power and torque bands.
With EFI, the engine will probably be more reliable, will run smoothly,
be more economical (as fuel is not wasted) and have a longer lifespan. As the
engine will be more fuel efficient, the combustion of the intake charge is
better controlled resulting in fewer emissions, little or no carbon build-up
within the engine and of course be much better to drive.
EFI ECUs can actually help prevent engine damage by not allowing full
power and torque to be generated until all fluids are up to their normal
operating temperature (an anti-thrash mode of sorts!). Nasty
pre-ignition/pinging/detonation can be a thing of the past thanks to knock
sensors, at the slightest hint of detonation the ECU can slightly alter the
ignition timing to fend off potential damage.
Instead of having heaps of gauges
on the dashboard, just look at the EFI ECU handset and they'll usually display
everything from engine revs to oil pressure to the injectors' duty cycle (the
amount of time the injectors are supplying petrol). Some brands of EFI ECUs have
dashboard displays and data loggers (like some of the MoTeC ECUs used in Touring
Cars) which would probably look fantastic mounted above your Mini's steering
column. EFI componentry can also look damn good on a show car. A polished fuel
rail, shiny braided fuel lines and gleaming intake trumpets can have crowds
swooning.
If you are a serious racer and want to cut down your lap times, consider
EFI closely, as some of the high-end EFI ECUs are excellent at data logging.
Imagine being able to retrace every lap you've just done back in the pits on
computer like the Touring Car guys do looking for ways to improve your car OR
your driving. You can compare a multitude of different types of data such as
speed through each corner for each lap, top speed at the end of a straight or
even maximum engine revs. Make sure that the class your Mini races in allows
full engine management, some don't.
All after-market programmable EFI ECUs I have seen possess a special
cold-start function (no more playing with chokes), can automatically control
auxiliary thermo-fans, can easily accommodate forced induction (such as a
supercharger or turbocharger) and many more functions I don't have room to list
here. Some EFI ECUs also possess an anti-theft function (which can be turned off
if desired), such as a PIN-number that must be entered before the engine will
start.
Disadvantages:
The disadvantages of converting your Mini to EFI
are many. Ask yourself the following question: do you need EFI or are you and
your engine perfectly happy with carburettor(s)? You must think carefully about
what use your Mini gets. EFI conversions are only worthwhile if they are used on
vehicles where the ultimate in performance and drivability are desired. If your
Mini's main role is not really performance-based, I definitely don't see the
need to convert to EFI.
If maximising power, torque and drivability are necessary, EFI MAY be the
answer for you. If your Mini is used for venturing out onto our terrible roads
as well as used for any racing events such as circuit sprints, hillclimbing,
motorkhanas or tarmac rallies etc., then EFI's versatility MAY be of benefit to
you.
There is no point converting to EFI if you cut corners. If cheap or
inferior components are used (such as a fuel-only computer rather than a full
fuel and ignition computer) then eventually you will probably wish you'd never
started as the results are always far from satisfactory. You must also be
prepared to outlay a lot of money. EFI conversions are not cheap, in fact they
are usually hideously expensive. Steer clear of modern car's EFI systems, they
aren't readily programmable and are difficult to get working correctly.
Definitely stay away from mechanical fuel injection, a Weber or twin SUs will
outperform an old mechanical fuel injection system easily (and be much cheaper).
You must be prepared to install all the parts required for EFI. A return
line must be plumbed in (probably along with a new supply line), extra wiring
for sensors and power supplies must be installed along with a myriad of bits and
pieces to complete the installation. Only unleaded fuel can be used because the
oxygen sensor that the EFI ECU usually relies on for input are easily poisoned
by the lead in Super petrol (I'll briefly explain how EFI works later). To get a
fuel with a high enough octane rating, use Premium Unleaded with a bottle of
octane booster if running a high compression ratio (near or above 10:1).
Another factor to be considered is the time it takes to perform an
effective conversion. Programmable ECUs use 3-dimensional maps to calculate when
to fire the injectors and when to supply spark. Once the EFI installation is
nearing completion, all the maps must be calculated, setup and installed by
running the car on a chassis dynamometer (which is cheaper and easier than an
engine dynamometer) under all load conditions throughout the rev range. Without
these maps setup correctly it is a waste of time and money.
Electronic Fuel Injection conversions are not incredibly DIY-friendly,
once installed and set up, its best not to fiddle too much. Possible points to
consider are that EFI-equipped cars run very high fuel pressure (up to 45+ psi
easily, so don't muck around with it) and it's also easy to destroy an EFI ECU
and all of it's settings by playing around with the wiring, so be careful.
Finally, converting your Mini to EFI is a pretty big step. Due to the
reasonably large expenses involved as well as the time required for an effective
EFI installation, you might well consider this to be a good excuse for either
starting a completely new project or to renovate your Mini. Although expensive,
the most effective EFI conversions always start out with a completely fresh
mechanical package in a good, sound bodyshell. Everything from the engine,
gearbox and driveline package to the braking, cooling, electrical, steering and
suspension systems must be in top condition. Remember that it is always the
weakest link in the chain that breaks first.
How Electronic Fuel Injection (EFI) works:
Under full throttle,
the EFI ECU will try to maintain the optimum air/fuel ratio the engine receives
for maximum performance (a reasonably rich air/fuel ratio near 12:1) by
interpreting the data it receives from all of the input sensors in what is known
as 'closed loop' mode. The oxygen sensor mounted in the exhaust system provides
the air/fuel ratio. This sensor calculates the amount of oxygen present in the
exhaust gases and passes that information back to the ECU.
Once the EFI ECU has
figured out what to do after calculating and interpreting data from the input
sensors, it controls other output actuators such as the fuel pump control
electronic mechanism, radiator thermo-fan(s) and of course the fuel and ignition
systems. The fuel injectors are told when to open and how long they should stay
open. The longer the injectors stay open, the more fuel flows into the engine
(this is known as the injector's pulsewidth). The ignition timing is calculated
and then the ignition system's igniters are sent a signal at precisely the
correct time to tell the coil to supply a spark through the lead and into the
engine.
Under cruising conditions, or part throttle, an air/fuel ratio near the
'stoichiometric' level of 14.7:1 is maintained to aid fuel economy and throttle
responsiveness in what is commonly known as 'open loop' mode. Under minimal
throttle conditions, when slowing down etc., the EFI ECU maintains an air/fuel
ratio that is incredibly lean, near 16 or 17:1 (or more), to further aid fuel
economy.
The great advantage of an EFI system is that the EFI ECU knows how to
provide maximum performance and drivability for any and all conditions that the
engine may experience. From full throttle up a steep hill to zero throttle down
a steep hill, the EFI ECU can provide you, the driver, with the most power
possible.
For a typical Mini EFI conversion, the EFI ECU should receive information
from the following sensors:
* A throttle position sensor that tells the computer how hard your foot
is on the accelerator pedal.
* A crank angle sensor that basically tells the
computer where the pistons are in their travels.
* A knock sensor which
detects any sign of detonation (pre-ignition or 'pinging') which is where the
air/fuel mixture is exploding violently inside the combustion chamber instead of
as a controlled progressive brurning.
* A Manifold Absolute Pressure (MAP)
sensor which measures manifold vacuum (or boost!).
* The engine speed in
revolutions per minute, which, among other functions, informs the ECU whether or
not the rev limiter should be invoked.
* An oil pressure sensor as an
emergency input, if the oil pressure is too low, some EFI ECUs actually turn the
engine off after triggering a warning to the driver to restrict engine
damage.
* An engine temperature sensor to let the ECU know if a cold-start
function is required where the idle speed is increased along with different fuel
and ignition settings are used until the engine has reached a normal operating
temperature.
* An oxygen sensor that is plumbed into the exhaust manifold
that examines the exhaust gases leaving the engine and informs the ECU what the
air/fuel ratio is.
* Many other input sensors that can be used include the
temperature of the intake air (especially important for a Mini using forced
induction), a sensor indicating which gear you have selected and many more I
don't have room to list.
The parts required for a typical EFI installation: 
Starting from the fuel tank(s), fuel is pumped by a
small fuel pump (known as a 'lift' pump) through a high-quality fuel filter into
a cylindrical container called an anti-surge tank (which is also called an
'(anti-)swirl pot'). It is 
vitally important to maintain an
even flow of fuel to the engine, as forces from accelerating, braking and
cornering can interrupt the flow of petrol through the fuel system causing the
EFI ECU to receive incorrect data upsetting engine performance (lean mixtures
for a very short period of time etc). Fuel is then pumped from the anti-surge
tank into the fuel rail mounted close to the intake manifold preferably through
another fuel filter. This main fuel pump should be able to supply petrol at high
pressure (45+ psi) for the amount of horsepower 
your
engine may make. Don't get sucked in by the person trying to sell you a fuel
pump that is way too powerful such as a Bosch 'MotorSport' or VL Turbo Commodore
pump. All they do is circulate too much petrol through the fuel rail, heating
the petrol up leading to a lack of power.
Once the
petrol has reached the fuel rail, it sits behind the injectors waiting for them
to open and flow into the intake manifold. The amount of pressure through the
fuel rail is controlled by a fuel pressure regulator at the end of the fuel
rail, which delivers unused petrol back through a different fuel line into the
anti-surge tank to be used again.
The air flowing into the inlet manifold is
controlled by a throttle body, which is basically a 
carburetor without the fuel delivery system and all the associated
restrictions on air-
flows that they provide. Mounted
either in or just after the throttle body are the fuel injectors themselves and
their wiring etc. I can't stress enough that all components
used must be of the highest quality to ensure safety, legality and reliability
as well as performance. Remember that you only get what you pay for.
Two possible EFI installations for your Mini:
There are two
main types of EFI installations that could be used on Minis. Forget the UK Rover
Mini injection systems, they are crude, inefficient and downright nasty. I would
recommend you steer clear of them.
The most effective EFI conversions
for a Mini use a cylinder head with 4 intake ports such as
an Arden or Weslake 8- 
port head. Alternative heads like a
BMW K1100 motorbike 16-valver or a KAD or Jack Knight Twin-Cam 16-valve unit
would also be ideal (although price is ultimately the limiting factor). With any
of the above cylinder heads, the injection system can use two Weber DCOE-type
throttle bodies mounted in the same way as if carburetors were used.
If using a 5-port cylinder head then how about
trying something different? Using a Weber 45 DCOE inlet manifold, have the inlet
manifold's runners remade 
to point upwards towards the bonnet instead of back towards the
firewall (you'll have to the runners cut and re-welded). Use an IDA (down-draft)
throttle body with four injectors mounted around the throttle body and with a
nice big air filter poking out through the bonnet, it should look pretty mean
too. If non-turbo Mazda rotary engines can use IDA throttle bodies, why not us?
With four separate intake ports, the EFI can be run sequentially where
the injection of the petrol takes place in each inlet tract just before
combustion. With only two intake ports from a 5-port cylinder head, the EFI is
run in 'group fire' mode where all the fuel is injected at the same time. This
means that the air/fuel mix remains unburnt for two of the cylinders for a short
time while the inlet valves are closed allowing the speed of air/fuel mix to
slow down resulting in a slightly less efficient combustion process. Don't get
me wrong, a 5-port with 'group-fire' EFI is fine, it's just that a cylinder head
with 4 intake ports and sequential EFI is the ultimate in performance IF money
is no object.
There are several after-market programmable EFI computers that are
suitable for Minis, the MoTeC M4 or M48 computers are excellent for the serious
racer. The Autronic, EMS, Wolf 3D, Haltech and MicroTech range of products are
also suitable and quite easy to setup.
For more details or more advanced information, pictures or examples of
EFI conversions check out the following websites:
For MoTeC products: http://www.motec.com.au
For EFI equipment:
http://www.injectionperfection.com http://www.fueltronics.com.au
For
the Haltech range: http://www.haltech.com.au
For the Wolf3D
ECU range and various ignition systems: http://www.aems.com.au
For the EMS range:
http://www.pem.com.au/enginemanagement.htm
For
the Autronic range: http://www.members.tripod.com/~autronic
