Introduction

The Skyactive engine platform found in the ND MX-5 vehicles is a particularly complex system.  Throughout our development we’ve made an effort to balance our efforts in simplifying the tuning system, as well as offering RaceROM features in the limited free space available to us in the ROM.  This means our RaceROM offerings are slightly different than in other platforms as there are either simplified forms being used, or something altogether unique.

With a framework for the platform in place, we’ll be working with our dealers in order to balance the features for this platform, with the practical limits of the ECU.

Table of Contents

The Platform

The Mazda Mx-5 SkyactivG cars use a high compression (14.0:1) 1.8L or 2.0L 4 cylinder engine utilising direct injection with a high degree of freedom of cam timing on both inlet and exhaust cams.  This allows the engine to use many complex strategies to deliver high power and high efficiency for such a small capacity. The control system components are as below.

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Mazda have employed ion sensing technology to model per cylinder detonation, pre ignition and air fuel ratio and uses these in many of the airflow and ignition timing strategies to preserve reliability while maintaining a high as possible performance and low emissions.

Ion sensing involves measuring the electrical current flow after the spark initially bridges the gap between the center electrode of the sparkplug and the ground strap.  In the event of a misfire, no current flow can be easily detected, making it a fairly stable and accurate method of measuring misfires. 

The 4-2-1 type exhaust pipes have been adopted for the exhaust manifold to create an engine with a high compression ratio.

Two types of load and airflow estimation have been adopted for the intake air amount measurement to achieve stable combustion free from abnormal combustion.

• L-jetronic (The intake air amount is directly detected by measuring the amount of intake air flow using the MAF sensor.) MAF sensor adopted

• D-jetronic (The intake air amount is detected indirectly by measuring the intake manifold pressure (pressure between downstream of the throttle valve and intake manifold) using the MAP sensor.) MAP sensor adopted

• IAT sensor No.1 and No.2 adopted

To improve the fuel economy and emission performance, an electric variable valve timing control has been adopted for the intake side, and a hydraulic variable valve timing control for the exhaust side. The electric type is adopted for the intake side to achieve expanded valve overlap and delayed closing of the intake valve (enlarged intake valve opening angle). The Hydraulic Lash Adjuster (HLA) has been adopted to achieve the maintenance-free valve clearance.

• Intake side: Electric variable valve timing control with independent CMP sensor

• Electric variable valve timing motor/driver

• Electric variable valve timing relay

• Exhaust side: Hydraulic variable valve timing control with independent CMP sensor

Engine hydraulic pressure switching control (using Engine oil solenoid valve) has been adopted to reduce the oil pump operation load on the engine.

To improve engine reliability, an ion sensor has been adopted which detects pre-ignition.

Some other features Mazda have listed as advances with their SkyActiv technology are.

Sliding resistance reduction

• Rocker arm (with built-in needle roller bearing) adopted for cam-contact area

• Reduced valve spring load

• Narrowed down crankshaft journal

• Optimized piston skirt shape

• Lowered piston ring tension

• Lowered drive belt tension

• Suppressed chain tensioner load by stabilized timing chain behaviour

• Oil shower pipe adopted

Mechanical resistance loss reduction

• Optimized oil passage

• Optimized oil pump shape

• Engine oil control adopted

Cooling loss reduction in early stage of combustion

• Piston cavity adopted

Pumping loss reduction

• Variable valve timing mechanism adopted on both intake and exhaust sides for fine control of exhaust amount and internal EGR volume

Cooling efficiency improvement

• Air seal cowl and flaps adopted

• Optimized cooling fan shape

• Optimized engine coolant passage

• Optimized water pump impeller shape

Combustion efficiency improvement

• Multiple hole-type fuel injectors

• High-pressure fuel pump

Summary of Software

ProECU software has been introduced to allow reprogramming of the factory ECU in order to tune the necessary components of the calibration in order to allow for modifications and increases in power.  This is not a standalone repalcement ECU so you shouldn't run into the associated issues or disadvantages of setting up a purpose-built ECU and control system from scratch.

The software allows easy control over most factory parameters including:

• Boost Targets and wastegate control

• Target AFR

• Ignition Timing

• Fuel Delivery including fuel pump calibration (using the same style pump as OEM)

• Airflow Measurement and fuel compensation

Ecutek offers full control of forced induction on SkyactivG cars.  As such we offer a well refined product that should be able to cope with the full range of forced induction and naturally aspirated modifications. We have also detailed some instructions on both of the example ROMs (NASP and FI) to help you tune these cars along with an example ROM to get you started. The YouTube video of the ECU Connect app highlights the advantages of packaging the tune with the EVI-BT and ECU Connect. 

Below are some links to the newsletters detailing the progress we have made on the product
• EcuTek release Mazda MX-5 ND RaceROM Update - http://mailchi.mp/ecutek/ecutek-release-mazda-mx-5-nd-racerom-update
• EcuTek release Mazda MX-5 ND RaceROM update for forced induct... - http://us7.campaign-archive1.com/?u=3293297053d29d26e037ea32b&id=9ae74a9f47
• EcuTek release Mazda MX-5 Skyactiv-G Retail kits - http://eepurl.com/bIa8ur
• EcuTek release Mazda MX-5 Skyactiv-G - http://eepurl.com/bHgUc5

You should be able to expect around a 15hp increase for NASP tunes and about 250hp in total for forced induction modifications.  See the dyno plots below to gauge the expected results for these types of modifications.

To get started there is an NASP example ROM and logs for the above power graph, these can be used to compare the results you achieve and the corresponding log from the stock ROM.

PSM4EB-example-v1-en...bin

tuned 182hp (1) (1).csv

stock 166hp (1) (1).csv

The key changes on the ROM are:

• Increased intake cam advance over 6000rpm where the stock ROM appears to deliberately reduce the intake advance in order to reduce power.

• Leaned out target AFR slightly

• Raised cat temp threshold to reduce temperature-based enrichment.

• Changed ignition maps to use just the base ignition map with increased advance.

• Raised rev limit to get a little more top end power.

Forced Induction example ROM is significantly more complex the Logs below show the changes between the stock and the modified vehicle.

• The key changes to the ROM are
  Increased intake cam advance over 6000rpm where the stock ROM appears to deliberately reduce the intake advance in order to reduce power.

• Leaned out target AFR slightly

• Raised cat temp threshold to reduce temperature-based enrichment.

• Changed ignition maps to use just the base ignition map with increased advance.

• Raised rev limit to get a little more top end power.

• Made the FI pressure multiplier map match the boost ratio profile of the turbo kit

• Use the neutral torque override to drive the torque and desired load

• Enabled RR speed density and used this to determine airflow when experiencing positive manifold pressure

• Used the throttle limit tables to improve drivability

• Disabled the EGT correction

Programming

For information on how to program as well as flash recovery, check out.

• ECU Programming Overview

• How to Recover an ECU
  
  

For more software guides check out:

• Software Help and How-To

Tuning Guide

Accelerator / Throttle Control

Throttle control in the ND is heavily linked to torque demand.  For a more thorough investigation of how torque requests and accelerator control are linked check out our article Skyactive G - Driver Demand Acceleration Request

Throttle Limiting Map

This can be used on turbo cars specifically to prevent WOT at low pedal, as the ecu tries to get the airflow while the turbo is spooling, and then having a big throttle fluctuation as the throttle closes to regulate the airflow to the desired levels. It's nice when it works (Ford Ecoboost) but we don't have the maps to tune the response of the OEM strategy so use the limiter map.

Throttle Limit 

Sometimes the cruise control functions are limited by the throttle limit map as well so the map may need to be profiled differently than expected in order to allow the CC to work correctly (As Shown).

Throttle Limit Multiplier

Offers the ability to adjust the throttle limit profile as atmospheric pressure reduces.

Eff Open Area Multiplier for PR

Divisor of desired effective open area based on manifold pressure ratio, this should not need to be modified if the throttle has not been changed.

MAF Desired Transient Blend

Blend map to change how MAF transients are applied to desired MAF. Reduce the value to zero at moderate to high loads to help stop oscillating desired MAF and throttle. This can be especially useful in cars with MAFs near a supercharger inlet or in bad flow regions.

Throttle Effective Open Area

Desired effective open area used in conjunction with the Throttle vs Desired Area map. These two maps drive into each other with correction on each loop. It is complex and they shouldn’t need adjusting to keep the throttle open.

Throttle Vs Desired Area

Throttle Target Limits 2d & 3d

These two OEM throttle limiters are used as well as the RaceROM limiters.  Ideally these can be left stock and the RaceROM table is used instead.

Camshaft Timing

Mazda utilise an electronic Intake Cam VVT actuator to allow quick and precise wide range of movement.  With a maximum overlap from intake open to exhaust close is 92° allowing for huge amounts of blow through if not correctly calibrated.  In addition to using the cam timing for EGR duties, it allows the system to enact the “Mazda Miller Cycle at low loads.  This cycle allows the intake valve to stay open beyond the bottom of the travel and into the compression stroke causing a slight amount of the air fuel mixture to go back into the intake manifold during the initial ~20% of the piston’s compression stroke.  The benefit being a slight reduction of the effective compression ratio.  They also utilise a hydraulic exhaust cam VVT actuator to allow for maximised.  The basic outline of the cams and how it related to crank angle and injection period is shown below.  

They allow a wide range of movement (roughly 74deg), where the target position in the map is the advance or retard from the base stop position. The VVT has different target modes, for idle, cold start and normal operating temperature and the switch point between the modes is not known yet.

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Correcting for effects of VVT

In early testing it was found that VVT Intake cam angle has a profound effect on the VE of the engine, especially with the ND's very wide range of operation (74° crank angle). So it has been necessary to make some provision for this as the ND can on occasion transition between cam maps, or (seeming) reduce the cam advance to effect torque output or avoid detonation.

This function is still in development and will include additional maps for exhaust VVT and expand on the MAP weighting map. However it is quite useable in it's current form.

Intake Cam VE Correction

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This map is a simple multiplier that is applied to the output of the Speed Density Volumetric Efficiency map.

There is no live data to specifically support this map, however when back calculating "SD VE Calculated" from the MAF sensor, the effects of the cam correction maps are taken into account. So in reasonably steady state conditions "SD VE Calculated" follow "SD VE Estimated" quite closely when properly tuned.

Intake Cam Correction Weighting

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This effectively adjusts the effects of the "Intake Cam VE Correction" map based on Manifold Absolute Pressure, if the values in this map are lowered it has the effect of "flattening" the Cam VE Correction map, where this map returns 1.0 the Intake Cam VE Correction map is used as is, the result is as follows:

CamCorrectionFinal ​​= 1 - ((1 - CamCorrectionMultiplier) * CamCorrectionWeighting) 

Cam Timing Exhaust #1 & 2 (hot/cold)

These are standard maps that set a desired exhaust cam angle for different speeds and loads.  The output values are the amount of retard from the base position (most advanced angle 56deg BBDC). Maps one and two are believed to be high and low temperature, testing can be done on the dyno to see which one is used when.

It is believed that the large amount retard used at low loads on the exhaust cam is used to promote Exhaust gas recirculation through the manifold. When back pressure is significantly different due to higher airflow or exhaust blockages (like turbocharger turbines) significant changes may be required to these maps.  Especially as the load values with force induction will be exceeded even at low pedal % and engine speeds.

In the EcuTek Turbo charged Forced Induction example ROM the load axis was rescaled to allow it to compensate for the higher cylinder fill appropriately and more retard was used at higher RPM and loads to try get more out of the power stroke. The tuned profile looks like Below, testing should be done to confirm that the vehicle you are tuning responds in the same way.

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Cam Timing Intake - Hot / Cold

These maps set the target intake cam angle. Mazda have calibrated them to match the exhaust cam mapping and create the Mazda Miller Cycle

When forced induction is involved the profile of these maps will need to be altered significantly as the available airflow characteristics are vastly different. Tuning these maps for forced induction requires load axis changes and significant modification to the higher RPM and load cells, deceasing intake advance at lower RPM high loads and increasing the advance at high RPM high and low loads.

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Cam Timing Intake Idle

The intake cam angle target at idle. This may need to get adjusted if the idle blow through is higher than expected and causing issues.

Cam Timing Intake Idle Minimum

At different atmospheric pressure more intake cam advance may be required, and minimums can be set here.

Cam Timing Intake Limit

At low RPMs the cam timing is limited likely to prevent excessive blow through and overlap. These values should not need to be changed.

Cam Timing Intake / Exhaust Increase and Decrease Rates

There are increase and decrease rates for both cams, but these should not require adjustment.

VVT Max Load Input #1 - 3 (Cold to Hot)

The intake and exhaust cams have a load limit applied to them based on engine speed and intake air temperature. It is assumed that this was employed to try to reduce the likely hoot of knock by reducing the VE at high cylinder charge temperatures.

When FI is employed the load limits applied by these maps must be raised to allow the cams to access he correct regions of the map and use the correct cam timing. In the EcuTek FI example ROM these have been raised from 1.0 to 1.4 to match the load axis input in the Cam angle maps at normal AIT’s.

Fuelling

Fuel Target Tuning

The Target Fuelling strategy for ND is complex and is based on engine load with many protection modes and temperature control methods. It is basically split into 3 primary modes start up, part load, full load temperature control as well as two different fuel cut modes with corrections and limits are applied at various points in the calculation. There are fundamental differences between NASP and FI tuning that particular attention should be paid, such as accel pedal and temperature thresholds.  These are covered later in the document.

Mazda split the fuelling Control Method into zones

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While cylinder fill models and lambda targets derive the injection quantity the conversion and correction of the injector open time is restricted according to the above modes.

Start Zone = RPM < 500

In this mode the injection time is set according to engine coolant temperature (low engine coolant temperature = long injection time). After start corrections are also set for a specified time according to engine coolant temperature directly after engine start

• Low engine coolant temperature = large correction

• Low intake air temperature = large correction

Feedback zone (λ = 1) = All other times

In this mode injection time is calculated as a base amount using Cylinder fill and fuel flow coefficients. It also applies corrections for

• Warm up enrichment (low ECT or AIT) after start

• Short term fuel trims (AFR Error actual to target)

• Rear O2 sensor

• Warm up enrichment at high loads

• Long Term Fuel Trims (Learned value based on average value of A/F deviation amount)

Feedback zone (λ rich) = WOP accel and EGT above threshold

• Short term fuel trims (AFR Error actual to target)

• Warm up enrichment at high loads

• Long Term Fuel Trims (Learned value based on average value of A/F deviation amount)

• EGT Corrections (Based on the accelerator pedal opening angle or on engine speed and cylinder fill.)

Fuel cuts are determined as Injection time = 0 during

• Excessive speed fuel cut zone = Above Rev Limit

• Deceleration fuel cut zone = Accel pedal closed, above decel fuel cut off (DCFO) RPM and Vehicle speed

A heavily Simplified view of the strategy is below

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AFR Target

Our advice for fuel tuning is use the trims as your guide. Adjust your MAF/SD maps as you need to keep the trims to zero and you will be sorted.

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This is an AFR target table that is employed when the WOP (Wide Open Pedal) threshold is exceeded. In the OEM strategy there are 2x 2d maps (AFR Target - Full Load #1 / #2) the result of which is overwritten by the output of this map.

It is only enabled by checking the box in "AFR Target Override Enable"

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Typical usage will include lowering the WOP threshold to a level that corresponds to a value that gives loads in the region of 0.8 or more. This is primarily for turbo application and used to switch to a richer target AFR that is variable with load, and prevent Lambda 1 at part pedal but significant load due to boost. On our turbo ND we lowered the WOP threshold from 93% to 35% but you should test for your selves.

The WOP thresholds can be found in the Fuelling->Accel Thresholds

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Part Load Fuel target

From our testing the ND generally runs Lambda 1 at part throttle, except when in the transient mode (a fraction of a second) and when the catalyst temperature is above the cat temperature threshold map EGT control #2, it then richens up to the 3d part load tables.  It may also use the maps at part throttle (maybe at full throttle without kickdown button pressed on auto car).

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The part load fuel targets are the maps “AFR Target Part Load #1 (#2 and #3)” affect the target AFR the ECU will ramp down to the target value (CAT temp goes about 826°C) so you can lean these out to reduce enrichment when at part/full throttle.

WOT AFR target

The WOT closed loop throttle is well understood but very complex. The AFR target at WOT is controlled by the 2 2d maps, along with some very small offsets for load. However, the ECU is constantly monitoring catalyst temp, exhaust temp and presumably cylinder head temp, all it appears through modelling. It will always ramp towards the richest target when certain cat temp thresholds are met or exceeded.

You can make the car run the WOT target you want by zeroing out the 3d EGT control enable table, or one of the 2d correction tables. I'm also sure that if you don't change the 3d target AFR tables that there is another temp threshold that will cause the afr target to ramp towards the values in those 3d maps.

So, to properly control the AFR at WOT you will need to alter the 2d maps, the 3d part load maps, the EGT/CatT thresholds and/or the CatT control enable maps. I will need to check what thresholds do what when I get back into the office.

You NEED to do some testing at part throttle, it generally runs Lambda 1 at part throttle once out of the transient mode (a fraction of a second) and it then richens up to the 3d part load tables, but only once the cat temp has reach 826.84degC CatT. If you put lean AFRs in those tables to make the CatT uncontrollable it will then wait until 900degC before making the target richer again using the same tables to avoid high cat temp at WOT.