A Basic Guide to Electronic Fuel Injection
for Minis
By Cameron Otway

 

http://www.hotbricks.org.au/

 

 

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 or see me at a meeting:

 

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 EMS range: http://www.pem.com.au/enginemanagement.htm


For more technical articles by the members of the MODIFIED MINI CAR CLUB OF SOUTH AUSTRALIA. INC., go to http://www.hotbricks.org.au/.