mx5cartalk.com

Hey there,

Just wondering whether anyone has successfully installed an MPGuino in one of our Australian MX-5's (preferably an NB8A)? I've had mine sitting on my desk waiting to install for a while and despite doing hours of research and having everything apart (likely staring right at the solution), I'm still feeling a little over my head.



Basically it requires wiring up to:
12V always on power source
Vehicle ground
An injector signal wire
Vehicle Speed wire (VSS)

So far it's been easy enough to locate the four injector signal wires heading out of the ECU and I think I've found the VSS wire heading into the speedo (white wire, black stripe) thanks to the people of the internet past (it sounds like it's easier if the car had an auto trans and / or cruise control, both of which I don't - most similar discussions seem to be around NAs and mention needing a 5V pull-up added to the circuit - unfortunately while I have a good ol multi-meter, I don't have access to something like an oscilloscope to check out what these wires are sending).

Suspected VSS wire (white, black stripe)


Injector wires attached to the ECU in the passenger footwell (wires shown bottom far left corner)


If anyone else if following along hoping to figure this out, here are some of the articles that have helped get to this stage:

MPGuino General Guide:
http://ecomodder.com/wiki/index.php/MPGuino

VSS (US)
https://forum.miata.net/vb/showthread.p ... ost6925342

VSS (Again)
https://forum.miata.net/vb/showthread.php?t=249867

NA VSS (Discussing +5V Pull-up)
http://www.miataturbo.net/ecus-tuning-5 ... ing-59814/


Finally, regarding always on power:

Does anyone know if we can grab always-on power from the fuse box in the footwell with something like this?
https://www.jaycar.com.au/double-mini-b ... p/p/SF5125

Otherwise, any recommendations for where to grab a non-switched power source in the cabin?


Anyway, work in progress, I'm sure there's a way - once we've got it figured I'll tidy this up with the full guide for future reference.
Also hoping to make a little 3D printed enclosure for it above the steering column, but I obviously need to make it work first!

Thanks!

Nb mx5s have an electronic speed sender in the gearbox, so you should be able to tap that wire at any point where it's convenient. No clue about voltage etc, but it should be far easier than the NA which is the old fashioned mechanical sender.

12v constant you should be able to just tap the centre post of the fuse box (Use a ring connector to avoid cutting the main feed wire)
Make sure to add a fuse too

Alternatively, if the thing you're wiring in isn't going to draw a particularly high current you can use the 12v constant for the radio.

Droo on this forum installed an Arduino in his ADM NA8: viewtopic.php?t=55483
& think Cus at least started the journey: viewtopic.php?t=71720

Indeed, I started the journey ... then my laptop hard drive died and I've not had the motivation to re-code all of the cool stuff I did have.... ...I have intentions, but also a full-time job and a whole lot of laziness...

Arduino Installs in MX5s are becoming pretty commonplace now Lokiel has one in his car in place of the water temp gauge doing "cool stuff" (I don't remember, but it's cool!)

Noisymime has even built an entire ECU out of an Arduino Mega!

As for 12V power, Get your power from one of the switched 12v's in the car, based on droo's calculations, unless you keep your car on a charger or otherwise use it a lot, an Arduino will pull your battery flat in a little over a week. (unless they've spent the time to make power management work, in which case you should get over a month before the battery goes flat) if it needs to be always-on to remember the MPG stats, don't install it (a half-knowedeable coder should be able to make an ardiuno remember things between power cycles)

HKS is on the money though, the arduino will pull in about 50-100mA of power at "full tilt", so won't make a lick of difference if you tap into the radio power, and tap into the VSS (speedo) signal from the back of the instrument cluster, it'll be the shortest wire run.

Thanks heaps everybody, all very helpful stuff - exactly the answers I was hoping for.

I've seen droo's build before and was hugely impressed at what he managed (it was definitely part of the inspiration to give this a shot). Would love to have the time to learn all the required electronics and software skills to make something custom but decided to go with something a bit... simpler... for now

Glad that speed sensor is electronic, should make things easier.

Regarding power - all the instructions I've seen suggest that it requires power even with the key removed. I don't quite understand why none of the variations have been able to tackle this problem but fortunately the version sold here:
http://mpguino.wiseman.ee/eng/mpguino
- is listed as only requiring 5mA during sleep, so it seems like building a little fused circuit off of the center post of the fuse box is the way to go.

Much appreciated comments though - looking forward to returning to it!

So after much faffing about, progress!



All plumbed in and version 1 of the enclosure completed. Surprising how close the base calibration was - speedometer reads exactly correct and consumption not too far off - will see how it goes after the first calibration tank. Love the display so far, nice and clear and well thought out readouts. Of course it's still a long way from the wonders of OBD2, but that's no fun, right?

Still need to finesse the placement and enclosure design. No point spending too long on these things before working out the practicalities in real world use. Would like to keep it in the driver's field of view but not obstructing the instrument cluster (and avoid anything particularly tacked on or ugly). Here's the current iteration:



Once it's all confirmed as working and calibrated I'll put a post in here with a guide for anyone wanting to do the same.

Thanks again for the help, people of the internet!

Just an update on this, all working great so far. Has definitely been worthwhile to get some helpful data.

Lesson 1 - Driving style isn't to blame for my poor fuel consumption (hooray!). 100km/h on a flat bit of highway rarely records anything better than 9L/100KM (instantaneous), which seems pretty terrible? Also, it runs crazy rich when cold. Tried resetting the totals one chilly morning and managed 125L/100KM 3 minutes in to the start of my rather sedate commute.

Lesson 2 - Idle dip that continues to plague me sees instantaneous fuel consumption read "999" just before it kicks back up again - which seems to indicate that something's having to cut in to override the ecu's normal values to avoid stalling. Having replaced the TPS, cleaned throttle body, intake manifold and EGR, thinking it might be possible for something causing excessive load on the engine making itself known at idle?

I do get the lovely accessory belt squeal on startup despite being tensioned several times, so started thinking maybe something along that route is requiring more power that it should. Checked out the belts with my FLIR one on startup and noticed the alternator pulley built up heat very quickly. A dodgy bearing or another red herring?



Sorry, still haven't gotten around to doing up a complete guide of the process, most of the information is there, just need to go through and clarify the steps.