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With this update I finally complete the installation of the MegaSquirt ECU into the car. This mainly involves wiring up a throttle sensor, rebuilding the intake pipes for an air temp sensor, and installing a Wideband O² sensor.

When finished, the engine bay looked remarkably similar as before, with the notable exception being the shiny customised intake pipes that replaced the air-flow-meter. With the flappy MAF meter removed I’m now 100% reliant on manifold vacuum to regulate fuel injection volume, along with air temperature and throttle position.

A manifold vacuum hose was taken from the existing fuel regulator tap, and using a Y splitter, a new line was brought into the cabin area and plugged into the ECU. The MegaSquirt contains a MAP sensor that measures air pressure and is used to regulate fuel delivery.

It is recommended if possible to use a Throttle Position Sensor (TPS) when using a MegaSquirt ECU – these tend to improve throttle response with acceleration enrichment, but my model MX5 only came with a Throttle Switch (simply closed/open and no measurement in between). Fortunately, the 3spd Automatic MX5′s did come standard with a TPS and as they are a simple bolt on, I acquired a 2nd hand throttle body and soldered some wires to the connector.  To connect into the stock harness (and to avoid cutting it) I fashioned a plug using some plastic and stiff wire – the result is something that can be disconnected and yet be firmly secured to the existing stock plug.

The Air Intake Temperature (AIT) sensor needs to be mounted in the stream of incoming air and the first logical place seemed to be where the intake pipe would need to bolt onto the air-filter box. Unfortunately this required mounting the sensor right behind the radiator, and this resulted in unacceptable heat-soak (a condition where the sensor itself if heated to beyond the ambiant air temperature resulting in incorrect readings). I then had to move the sensor to inside the filter box, and this provided more regular air tempatures without heat-soak problems.

The final task was the installation and wiring of the Wideband O² sensor and this required installing a controller module within the engine bay (seen next to the washer reservoir). To enable the sensor, you need to supply 12V for heating of the sensor along with wires back to the ECU. The Innovate LC1 sensor (the type used here) provides a simple harness that I adapted to a DB15 connector that plugs into the DB15 port on the DIYPNP case. This provided a fairly simple place to mount the LC1 calibration switch and diagnostic LED – both of which are now mounted as part of my DIYPNP ECU case.
    

So, the final step is to connect the ECU to the stock harness, removing the original computer and neatly rest the new ECU into the protected cubby hole. After uploading a tune file (obtained from a fellow MX5 owner with a similar MegaSquirt ECU) I fired over the engine and it kicked into life – running a little roughly and spluttering to a stall when any throttle was provided, but it would start and idle reasonably OK. After a little tuning of the fuel maps, adjusting for acceleration enrichment, the car seemed to be running fairly well. Last step was to provide a method to easily connect to the DB9 communications port on the back of the ECU – so I added a ribbon DB9 extended assembled from $6 worth of parts from Jaycar.

Tuning the ECU is a subject I’m not going to cover here, but suffice to say I’m still doing it several weeks later and feel I’ve got a bit more to do to get it to behave 100% like stock… so you can have respect for the OEMs and the complexity that goes into modern computer engine management systems.

You can download my tune file for my car that would be a reasonable starting position for any similar NA6 owner who is keen to start at known good position with a recent firmware from MS2/Extra – at this time its based on the 3.2.0 release.

All-righty, I’m up to the stage where you hope it works and will allow you to load some firmware. There are no status lights or electronic display to tell if you if anything is right or wrong, so you rely totally on getting a connection to a standard computer verify the unit is working.

First step is to download the needed tools – which comprise of the latest firmware from the forum section of the MSExtra website and the tuning software TunerStudio from  EFI Analytics. You can use the free version but for ~$50 you can get a pro version that includes auto-tune and a great log visualiser.

Next you plug the device into a USB-Serial cable and get Windows to discover and enable the Com port – remember this number (mine was Com4).

I downloaded from MSExtra the released version of MS2 being 3.1.0 and the zip file contains two .s19 files that are the binary firmware images (one for Megasquirt, and one for the DIYPNP with the Microsquirt module). Inside the zip is a windows batch file to download the firmware. You run this and it asks questions, you follow and it will upload the boot code and then you repeat and it then loads the firmware.

Once complete you can fire up TunerStudio and it will detect and connect to the device. Next you load a base tune (which I used from the DIYAutotune website for my model MX5. This base map sets the common settings for Cam wheel sensors, fuel injection sizes, spark and crank settings etc. It helps start the car and getting it to run, but you then need to fine-tune to ensure it runs correctly.

A good video of the setup and tune process…

Now the fun begins as I install the ECU into the car, and add a Variable Throttle Position Sensor to the existing throttle body, wire it up and start the tuning.

Okay, time for an update. This step is essentially the initial assembly and build of the entire ECU. If you’ve ever done hobby electronics building, you’ll find this really easy as the boys from DIYAutoTune have done a great job in terms of marking everything and providing detailed instructions.

Considering the kit targets a large number of vehicles and models, the additional steps for my MX5 were mostly clear and available. I did find a few areas a little puzzling, but nothing where I had to specifically ask a question, as often the answer was available on a forum or a re-read of the guides eventually provided an answer.

I ordered the sequential injection add-on board which brings the total number of injector drivers up to four (4) from the default of two (2). I could have continued running with Batch injection, which at high RPM produces similar performance and ecconomy, but if I ever decide to upgrade to larger injectors (and I do) then having sequential will help with low RPM idle and fuel ecconomy – as firing a bunch of large injectors when the time for the next injection is long (as it is with low RPM) results in wasted fuel, wet walls and other bad things!

As far as assembly goes, the first thing to do is to fully read and re-read the entire assembly instructions including the additional application notes for the year/model MX5 I was building for.

I soldered and assembled in front of my study computer and left these two (2) websites open in front of me.

http://www.diyautotune.com/diypnp/docs1_5/main_assembly.html

http://www.diyautotune.com/diypnp/apps/n76/usdm-mazda-miata-9093-16b6-mt.html

That way I could solder/assemble and re-check the guides to ensure I was on the right path. As each component was individually marked and bagged, there really is little chance of doing the wrong thing – obviously this assumes you’ve used a solder iron in anger, and know your way around electronics – which I do/did.

In addition I also downloaded the Startup Maps zip file which contained a Excel spread sheet of the jumpers and hook-ups needed. This document helped explain what features you were taking from the standard harness and connecting into the MegaSquirt board. Obviously at this stage you are complete and really performing the final assembly/soldering steps.

I also grabbed an OEM ECU pin-out guide that I found on Miata.net, a copy of both are included here as images that you can click on to enlarge.

So after about 3-4 nights spending about 2 hours each I completed the entire kit and was ready to switch on and upload firmware etc. Next blog will cover off that process and further progress.

I’ve decided to embark on what will be a fairly interesting and lengthy project - to build and tune my own Engine Management System.

Based on the very popular MegaSquirt kit, I ordered a DIYPNP (do it yourself | plug-n-play) plus a few other bits from the guys at DIYAutoTune.com in the USA.

Specifically I ordered the following:

1. a DIYPNP Nippon Denso 76pin (that suits the MX5) that is essentially a MicroSquirt module, mainboard and case that provides MegaSquirt2 capabilities.
2. an Intake Air Temp sensor kit comprising a bung and all needed wires, connectors and something to simply plug straight into the existing MX5 harness (this will allow me to delete the restrictive Mass Air Flow meter).
3. a sequential injection upgrade (that allows 4 injectors to be driven).
4. a Serial-to-USB connector so that I can plug my notebook into the kit.
5. an Innovate LC1 wideband O² sensor and controller (that allows me to measure the entire range of O² levels in the exhaust).

After parting with some ca$h, I waited just around a week for the package to arrive. Inside a neatly packed box was a well protected collection of plastic bags and boxes. Kit assembly seems to require at least basic soldering and some electronics experience – the required tools are fairly modest – a good quality soldering iron, digital multi-meter, a collection of tools for cutting/stripping and perhaps wires etc.

No instruction manual or guide book was included, but a link to a website where you can follow instructions for assembly. Considering the low cost nature of the kit, and the fact that it limits the killing of trees, I’m actually glad they didn’t!

The on-line instructions essentially direct you through each phase starting with low height components (resistors) and then ending with the tallest components (being the MicroSquirt daughter card).

A nice feature is that all components are neatly bagged and bundled with quantities outlined, so that each is essentially individually labelled. As they are marked, you simply just have to find the part on the PCB, insert correctly and then solder. So the kit is fairly easy to follow, and if you take time, should be a simple assembly process.

For my next post, I’ll hopefully looking at assembling the case, adding jumper wires and powering up the ECU for initial firmware and software configuration…