This Blog is written from our content with the UK’s MX-5 Magazine, Soft-Top-HardTop.
10 Minute Tech
ECUs
Each issue we quiz a specialist with 10 quickfire questions about a product to give you the knowledge you need to make the right decisions when it comes time to upgrade. This edition we speak to Bofi Racing to get the lowdown on ECUs…
1. What is an ECU and what does it do?
A car’s ECU, or Electronic Control Unit, is the brain of your car and is programmed to control all of the electronic elements of your car. Modern cars can have multiple ECUs to control other aspects of the car’s electronics too such as electric windows, security devices and in car entertainment to name a few, but in this article we are focusing on the main control unit that runs the engine.
By receiving inputs from an array of sensors the ECU, which is pre-programmed with multi-dimensional performance maps (or lookup tables), can determine the correct output response for a series of actuators which allow the engine to run correctly. It can control aspects such as fuelling, ignition timing, variable valve timing and idle speeds. In forced induction engines it can also control boost levels, but more complicated ECUs are able to control many more engine parameters too.
2. Are all ECUs the same?
In concept they are largely the same in that they all use a printed circuit board and various microchips and electronic components but, like most electronic devices, they are set apart by the software and quality of the hardware used. Some are able to be remapped while others can’t and some offer greater levels of adjustability, expansion and control than others too.
3. Why not just Remap?
If your ECU is remappable, which in the case of the NC and ND generations it is, but with the NA and NB models it absolutely is not, then you certainly can go down the remap route and extract better performance and fuel efficiency from your MX-5’s engine while retaining your car’s factory ECU.
However, bear in mind that additional remapping would be required every time you make a modification to the engine (within reason) which can often come at a considerable cost, as it would have to be undertaken by a specialist tuner with the correct hardware and software, whereas an aftermarket ECU can be remapped endlessly via your own laptop for free, if you take the time to learn what you are doing. Obviously, if you have a Mk1 or Mk2 then remapping the stock ECU is not an option and an aftermarket ECU is your only choice.
4. How do aftermarket ECUs differ from OEM ones?
A stock ECU has been designed within a fixed remit to be reliable and as efficient as the emissions rules dictate at the time of manufacture. This means there are certain trade-offs that the OEM ECUs make that limit the potential power available from the engine.
This is because running the engines at a more aggressive state of tune would compromise their reliability when used with the lower grade fuels and extreme climate conditions that are found in some of the global markets that the car is available in. The software of some ECUs can be adjusted via remapping to limit these trade-offs to a certain degree, but others, such as those on the NA and NB MX-5s, do not have this facility and are not able to be adjusted.
As an aftermarket ECU is fully programmable you can completely eliminate these trade-offs and can run the engine exactly as you want it according to the modifications you have installed, the fuel you choose to use and the conditions you will be driving in. This means you can push the level tune and therefore the power the engine can make much higher than would otherwise be possible.
5. Why, or when, would you need to upgrade your ECU?
You would require an aftermarket or ‘standalone’ ECU in a scenario where you either want to make continual changes to the car or the map and/or you need additional sensors that the stock ECU doesn’t have provision for. Alternatively, you may want to add forced induction, which the stock ECU doesn’t have the capability to handle, or if your car’s ECU cannot be remapped to take into consideration engine modifications such as those on NA and NB models.
6. How important is type of ECU used?
As with most aftermarket parts, there are levels to the types of ECUs that are available, with some being more suitable to general road and occasional track use while others are best reserved for full-on track machines. Generally, most people will want what is known as a ‘Plug and Play’ ECU, which uses the factory ECU wiring connector.
This has its limitations, but for most platforms – unless you’re building a full-on racing car with an obscene amount of additional systems (such as nitrous, wheel speed sensors, oil pressure, temperature, flex fuel, fuel temperature, crankcase pressure, exhaust gas temperature, multiple O2 sensors etc) – a Plug and Play ECU will be more than adequate. With that being said, the likes of the Motorsport Electronics ME221 and ME442 ECUs are Plug and Play units which have more spare inputs and outputs than even the most heavily modified MX-5s will ever need, even those running over 500bhp, so buying an ECU much more complex than this would likely be a waste of money.
7. What are the limitations of factory ECUs? Do aftermarket ECUs have the same limitations?
As we have already mentioned, factory ECUs have limitations in that some cannot be remapped or adjusted at all, and some, while possible to be remapped, often offer very limited adjustment with few options for expansion or additional control. Aftermarket ECUs on the other hand are far less limited and are typically only restricted by the software and the amount of input and outputs. They can be split into two camps: Plug and Play and wire-in.
Like Plug and Play units, wire-in units (also known as standalone ECUs), are much the same but do not use the factory wiring harness and generally come with much greater control options. This makes them more expensive to buy and more complex to install, again adding to the cost, which leads them to being more suited for those making a custom engine harness or building to a competition specification.
On the flip-side, you can purchase cheaper wire-in units that are even more limited by design, specific to the minimum requirements needed for the engine / car being built. Typically, the software is the core limitation for aftermarket ECUs, so choosing one that has continual support, updates and general innovation is key.
8. What other mods should you consider when fitting an aftermarket ECU?
If you’re putting an aftermarket ECU in your car you will immediately benefit from using a wideband oxygen sensor (with some ECUs, such as the ME442, this is included with the package). This is because it allows fine-tuning of the fueling, allowing you to optimize for power and economy, even on an otherwise standard engine! Fueling isn’t just a set amount, it varies via throttle position, RPM, engine load, temperature, and other factors, so the ability to map this against the real-time inputs from the sensors is critical to maximizing performance regardless of any other performance modification that may be fitted.
9. What mods require you to have an aftermarket ECU?
If you’re going to keep your car naturally aspirated, and your ECU is compatible (NC and ND models), you might be able to get away with remapping, but whatever generation of MX-5 you own, if you are considering some kind of forced induction, such as a turbo or supercharger – or if you’re staying naturally aspirated, but want to install a set of individual throttle bodies – then you will have no option but to make the jump to an aftermarket ECU.
This is because safely turbocharging an MX-5 engine to much above 160bhp requires larger injectors, which need a different ECU to control the amount of fuel they provide. Also the timing of the engine needs continuous adjustment in real-time (not just setting a base timing) as the car comes on boost. Individual throttle bodies also require a different method of controlling the fueling as, for the best result, this needs to be done purely based on the throttle position, something that the stock ECU can’t do.
10. Are there any downsides to aftermarket ECUs?
Aftermarket ECUs have many benefits if tuned correctly, such as the complete control over basically all aspects of the tune, live through your laptop. However, they can also be a double-edged sword, in that because you have so much control, it is easy to get things very wrong if you don’t know what you are doing, and it’s quite a lot to learn, which is highly recommended if you are considering tuning the car yourself.
The other potential downside to aftermarket ECUs is that the mapping will obviously not be as heavily developed or tested as Mazda’s factory ECU in all climates and conditions, so can take time to dial in an OEM-level of cold-start in all conditions. It’s also quite an expensive modification both in terms of the hardware and setup (even a basic Plug and Play system starts at around £900), but one that will continue to reap benefits for the life of the car, especially if you intend to continue to carry out performance modifications.
11. Other than ensuring you get the right ECU for your application, what are the most important things to look out for when buying an aftermarket ECU?
Long-term support both for the hardware and software is crucial, as is finding a reliable tuner that you trust and is willing to work with the product you have selected. Obviously, like any purchase you make, buying from a reputable brand, that specializes in the platform and has good support from the manufacturer and tuner networks that are on board, developing, improving and testing products on a day-to-day basis is worth its weight in gold.
Finally, ensure you fully understand what your longer-term goals are for the project: is this something you’re keeping as a platform to modify, compete with and grow as a hobby or is this a means to an end where you will be happy with the level of tune after the initial set-up? You don’t want to go for a lower specification option only to end up having to buy another higher specification unit if it is not suitable for your needs further down the line. Luckily, most of the Plug and Play ECUs, especially the ME442, have such a wide scope that you’ll be hard-pressed to ever require the next level up even with a full-on track build.
