Some Basic info

As modern automotive development has advanced there have been many developments that have allowed engine efficiency to be improved, the average petrol engine is only approximately 50% efficient in terms of the potential energy contained within the fuel compared to the useably power it delivers at the wheels, (diesel engines by comparison are about 80% efficient). Most of the losses are through thing like heat and the power-train, but some come from inefficient technology.

Nearly all modern cars are equipped with multi valve technology and also fuel injection, this is partly as a result of the advancement of such technology and partly out of necessity, with ever more stringent emission control regulations items like catalytic converters are needed, these unfortunately restrict exhaust gas flow and rob power, this power deficit is made up by improvements elsewhere.

EFI is one of these advancements that has become practically a necessity. For modern catalytic converters to work correctly the fuel delivery has to be very precise, this is almost unachievable with a carburetted car too much or too little unburned fuel will reduce the life of a cat considerably.

Power gains are obviously made with EFI, the correct amount of fuel can be supplied to the engine at all times, thus improving efficiency and in turn power.


So what's wrong with carburettors?

Carburettors are pretty crude in their operation, their basic function is as follows.

The engine sucks air into the cylinder on its downward (induction) stroke, this air is sucked through a section of tube in which there is a device for restricting this flow of air (the throttle butterfly). If you placed a piece of tube in this airflow pointing towards the engine air would also be drawn through the tube, now put the other end of the tube in a container of petrol, the petrol is drawn through the tube and into the engine. This is a (very) basic carburettor. The amount of fuel is metered by the size of the end of the tube, this end is also designed so that the fuel is atomised and does not 'drip' into the engine, the component that does this is commonly referred to as the 'jet'.

There are two main problems with carburettors, the first is that at different engine speeds (read: induction air flow), differing amounts of fuel are required. With only one jet this cannot be achieved as the required air / fuel ratio is constantly changing. 'Twin-choke' carburettors attempt to overcome this by having a second jet that it activated at higher airflows or at different throttle positions, SU carburettors us a moving needle that moves with the airflow passing through it rising up when more air passes, allowing more fuel to be sucked into the engine. With all of these different methods employed, whilst they may be improvements over earlier more crude designs they are far from accurate. The inaccuracies in these carburettors ability to deliver the correct amount of fuel for any given air flow causes a greater potential for problems like detonation, this can be largely due to lack of fuel. Compensation is made for these issues by changing things like the advance curve of the distributor, thus reducing or eliminating the possibility of detonation due to the carburettors inefficiency but causing a reduction in power due to the far from ideal ignition timing across the rev range. This is why 009 Distributors 'improve' power, their advance curve is much different from a standard distributor.

The second problem with carburettors is that at low engine speeds the air flow is not high enough to cause an accurate amount of fuel to be drawn in through the jet, the response in the jets ability to deliver fuel, compared to changes in air flow at low air flow speeds is also very poor. Accelerator jets are used to overcome this sluggishness, these are additional jets that supply a pre-measured additional amount of fuel to be 'squirted' into the carb when the throttle is pressed quickly, this by it's very nature is a very inaccurate way of overcoming the low air flow / fuel delivery response.

Most carburettors are jetted so that at wide open throttle (WOT) the fuel delivery is correct, in this respect the overall power gains are perhaps not as great as you would expect when fitting EFI, this is obviously only compared to (a) correctly set up carburettor(s). The biggest gains are to be had at lower engine speeds. As EFI actually sprays the fuel into the airflow it is completely independent of the air flow itself, not requiring the air to draw the fuel into the engine as in a carburettor, the response of the EFI is also better as the amount of fuel delivered is controlled by sensors that monitor the throttle position, manifold pressure / vacuum, and possibly also the airflow itself, so for any given demand the exact amount of fuel can be delivered.

The use of sensors to monitor engine conditions is the key to the success of EFI, if you can measure how much fuel is required, and then control the amount of fuel delivered the fuel delivery system becomes what is known as a 'closed loop system'. Whilst air flow may seem like good way of determining these requirements the only way to accurately control this is by monitoring the amount of fuel needed by the engine, whilst air flow gives a good indication of this, it is far from accurate.

After the engine has drawn the fuel into the cylinder, compressed it and then ignited it to produce the explosion required to turn the engine, the waste gasses are passed out through the exhaust. During this process oxygen is used to fuel the explosion. by measuring the amount of oxygen left in the exhaust gasses we can determine if the correct amount of fuel has been supplied, too little fuel and an excess of oxygen will be found, and vice versa. There is a finite amount of oxygen that should be present, this amount is derived by the fact that to burn 1Kg of fuel 14.7Kg of air is required, now for complete efficiency you would then expect to find no oxygen present at all, but this does not tell you if you have too much fuel, also extra unburned air helps to quench the explosion, this air also expands by an amount thus causing a better exit flow of the exhaust gasses due to the pressure differential between inside and outside of the cylinder.

To measure the amount of oxygen present in the exhaust gasses a lambda sensor is used, this is basically a switch that switches when a certain ratio of oxygen is found (it compares the exhaust gasses to the outside air). At the point of switching the sensor will change state, this is not an on / off type switch, but one that produces a change in the voltage across its output. Between the different sensor states the change occurs gradually, this 'gradual' change can be used to measure the amount of oxygen present. Whilst this change is gradual, the full range that it operates across is only very small, but it is enough to be able to decide on the amount of fuel needed by the engine.

Wide Band Lambda sensors.

There is a better type of lambda sensor available, this is known as a wide band lambda sensor, because this operates across a greater range, it is a far more accurate sensor than the normal lambda sensor, however it is a lot more expensive. Normal lambda sensors have either 1, 2, 3 or 4 wires. The wide band sensor is easily distinguished by the fact that is has 5 or perhaps 7 wires. Some makes of EFI will allow for fitment of a wide band sensor, some won't. It is possible to get adaptors to allow them to be fitted but it is worth checking this with the manufacturer before parting with your cash.

What should I look for in an EFI system?

There are lots of considerations when trying to find a suitable EFI system, perhaps the biggest governing factor is cost, some of these systems can be very expensive. Whilst limiting yourself to a budget may seem like an obvious necessity, it may be worthwhile considering paying a few extra dollars rather than end up with a sub standard system.

At its most basic level the EFI unit will replace only the carburettor(s). Some can also be used to control the ignition, thus doing away with the points. Then there are the systems that do away with the distributor completely. At the other end of the scale the EFI unit can have functions to control all sorts of things, such as; launch control, shift lights, turbo waste gate control, traction control, data logging, variable cam timing etc... There are some systems that have completely programmable outputs so that you can control anything you want.

Not all systems can be used with a lambda sensor, for these units the fuel is metered by either throttle position, airflow and / or manifold pressure / vacuum. whilst these systems are still far better than carburettors, they are not as good as a closed loop system. This is definitely worth bearing in mind.

Most of the systems available on the market currently are 'real time programmable', this means that you can change the settings as the engine is running, usually this is done by plugging a lap top into the controller and using special software, sometimes the unit will come with a dedicated programming controller, this is used instead of the laptop. very basic units come supplied with only a box with some knobs on it, these are used to set the mixture in much the same way as adjusting a carburettor, again whilst these units offer advantages over a carburettor they are not as good as the units requiring a laptop or controller to program, why will be discussed later. The units that are not real time programmable are possibly amongst the cheapest, these are usually converted OEM units (the GM ECU is the most common used), however they are very difficult to set up accurately, this is because you cannot make adjustments as the engine is running the settings either have to be downloaded with the unit not running, or even written to a microchip that is then fitted into the ECU, thus it is very hard to get all of the settings absolutely correct - unless you have the patience of a saint.

Technical stuff

Ok, earlier I said that the type of EFI that used a control box with just a few knobs on it wasn't the ideal unit to use, this does depend upon the application, it is probably not suitable for a high horsepower engine but probably perfectly adequate for someone who's running a stock or mild street engine. Here's why.

Most real time programmable EFI units operate in the same way, they have stored what is know as maps, usually a minimum of one for the fuel and one for the ignition if this is also controlled. These maps basically tell the engine what to do. The map (as shown in picture) tells the EFI how much fuel is needed for any given engine speed / load. Other maps act as compensation, for example the fuel may need to be adjusted due to the lambda voltage, or for turbo engines it may need to be increased when the manifold is under pressure (turbo boost) for each of these functions a map is required.

Each position on the map is usually referred to as load site, the more load sites the maps have, the greater accuracy they system will operate to (the resolution of the system is increased), some systems use fixed load sites, this means that they are set out at equally spaced intervals that cannot be changed. This may give a problem, if a 'flat spot' is discovered in the setting up it may be because more accuracy of control is needed at certain points in the map range (say at a given rpm), with a system that does not use fixed load sites it is possible to redistribute / add extra load points where they are needed.

The basic systems use a fixed map, the control box with knobs on it is used to adjust the map across its range, not at individual points, thus it is not as good as a fully real time programmable unit.

To utilise an EFI unit with a turbo it must have positive manifold pressure compensation, this pressure is read by a sensor called a MAP sensor (Manifold Actual Pressure or something like that), when a boost condition is detected by the MAP sensor the fuelling is increased accordingly (more pressure = more air = more oxygen = more fuel required) too little fuel and the mixture will be too lean, this causes detonation that in turn causes engine operating temperatures to rise and can lead to melting pistons. So if you are running a turbo, make sure the system can handle it.

After considering these factors the next things you'll want to look at are the extra functions supplied, below is a list of some of the functions that can be controlled by EFI units.

• Turbo waste gate control
• Water injection
• Nitrous control
• Rev limiters
• Shift lights
• Tacho outputs
• Ignition control
• Distributor-less ignition control
• Extra injector control
• Launch control
• Traction control
• Sequential gearboxes

Most systems come with programmable outputs, these can be either volt free contacts or PWM (Pulse Width Modulated). the outputs can be programmed to open or close at different engine revs, manifold pressure etc. the PMW outputs (the same type of output used to fire the injectors) can be scaled to operate across the complete range of revs / pressure etc. these outputs can be used to control all kinds of fancy gizmos. If you're feeling kinda technical, why not make a variable length exhaust system, like those found on Mitsubishi 3000 GT's, hook up the PWM output through a driver stage to a stepper motor to change the length of the exhaust at different engine revs, well maybe.


What else do I need to know?

The best way to find out what kind of system will suit your car is to visit the web sites of all of the manufacturers, each will have a load of jargon and sales literature telling you why their system is best, and explaining in detail what all of the bells and whistles do, once you've been through all of the sites you should have a better understanding of what is available, and can then make a more informed decision on what you will need. try searching for 'EFI', EFI kit', Fuel injection'... you get the idea. Pay attention to things like what comes with the kit, most will only include the ECU and not much more, the wiring loom, programming lead sometimes even the software may cost extra, this soon adds up. A lot of manufacturers have free downloads for the programming software allowing you to 'test' it.

A question for most people will be 'how easy is it to set up', for a lot of people this will more than likely fall outside of the scope of what they are prepared to do themselves. All is not lost, most of the manufacturers will be able to point you to someone who can set the system up for you, lots of rolling roads perform this service, a charge is made by the hour for the use of the rolling road, and a further charge is made for the use of a technician, make sure they are familiar with the type of system that you have.

Lots of kits will come with a basic map that should allow you to start the engine, this gives a base from which to work from. Anybody who is familiar with computers should be able to operate the software but it will take a more experienced person to know how to set up the fuelling and ignition maps. When doing this on a dyno the maps can be dialled in quite quickly as the dyno will display real time what is happening with the engine output. It is also possible to do this 'on the road' so to speak, but this will require a much greater feel for what is going on. This approach may be ok for the motor-racing world, but is beyond the scope of most of us.

There is one (or perhaps more) systems that can plugged into the dyno, this makes setting up a piece of cake with the ECU practically tuning itself. When using a dyno what you have to do is to balance the dyno load with the engine rpm, once this has been done you can then alter the settings of the ECU to give the best power output. the hardest part of using the dyno is initially matching the engine / dyno speed and load. With a system that can control the dyno, or be controlled by the dyno this part is taken care of leaving just the map adjusting to do. If the ECU utilises a Lambda sensor it is possible for it to practically tune itself, as it can automatically compensate for changes required in the fuelling map. Ultimately the best way of setting up is to utilise an experienced technician as they may well tell you that a little more fuel here and there will improve the power, this differs from engine to engine and is largely linked to things like the camshaft, porting job, length of manifolds etc etc... an experienced technician will be able to read what's going on and set the ECU up accordingly.