MegaSquirt 2 Extra and LC1 Wideband Parallel/Boomslang Install on a 97
I realize it's generally frowned upon to do a parallel install, but I have a '97 and it's a daily driver so I wanted to be able to pass the NC inspection with my turbo'd Miata. Before making any changes to the stock motor, I wanted to get my Megasquirt up and running. After a huge amount of reading, a lot of soldering and a few hiccups along the way, I got the car running nicely on my MS2 Extra and thought I'd share my experiences.
I split the project into a few steps:
1) Get the wideband O2 sensor wired in (Innovate LC-1)
2) Build the MS2 Extra and harness
3) Get it running!
Step 1: Fit the wideband
My plan was to fit the WBO2 sensor first so I could get some idea of the stock AFR at full throttle and during a cold start. I also wanted to check the stock ECU was happy with the signal from the wideband sensor.
I went for the Innovate LC-1 as it has 2 analog outputs and was cheap. I was a little worried about comments of poor reliability, but I had no problems and would recommend it.
Iíve attached a schematic of the wiring harness I made for this, which worked really well. The idea was to wire in the LC-1ís second analog output to the stock ECU, configured as a narrowband output (as it is as supplied). I then used the first output connected to a voltmeter to monitor the real AFR (too tight to buy a gauge at this stage!). To stop the stock ECU throwing a code due to the stock O2 sensor heater not being connected (which it would), the harness allows the stock O2 sensor to be connected to the heater circuit. I just strapped the old O2 sensor in the engine bay, but long term a high wattage resistor would probably suffice and keep the CEL at bay.
You might think I've gone a bit overboard on the grounding, but in my book that's the right side to be! Grounding issues are a PITA. Also, I attached the 12V supply to the wiper fuse, as it's live only when ignition is on (not cranking), which was recommended by a few people on this forum.
So, a few observations: full throttle AFR was around 12.7 to 13.0 and from a cold start it was as low as 10.0, quickly rising to stoich as the motor warmed up. Nothing surprising there, but worth checking.
Thanks for your support 18psi! My decision to go parallel was purely based on wanting to pass inspection without having to put the stock ECU back in. Obviously not a problem for pre-96 cars, but a very real issue for those of us with an OBD2 port.
There were several other advantages too:
1) If you're only controlling spark and fuel using your MS, it's only a minor harness wiring change to switch these outputs back to the stock ECU while still having the MS2 fully wired in to all the sensors. I actually wired mine like this initially, so I got several hours of data logging from the Megasquirt to make sure my crank sync was stable up to the limiter, I had sensible sensor inputs and it was demanding sensible fuel and timing. All with no risk to the motor!
2) Initial startup is easier if you only have to worry about spark and fuel. The stock ECU controls airflow and idle speed. Much less daunting for the first-timer.
3) The stock ECU still gives OBD2 diagnostics that you can trust. I had an OBD2 logger plugged in as well as my MS2 when first starting, just to make sure it was happy.
4) A very minor thing, but the MS build is probably marginally easier as you don't have to worry about the fuel pump, A/C idle up, dash outputs etc. I know they're easy, but you still have to do them with a standalone.
The main disadvantage as far as I could see it was a more complex harness. Not difficult, just (quite a lot) more work. I haven't got as far as modifying the engine yet and I'm sure that'll bring a few headaches such as giving the stock ECU a MAF and IAT signal, but for me as a first-time Megasquirt builder, the parallel route has worked out really nicely so far.
The MS2 build was actually quite straightforward, once Iíd decided on the features I wanted and done the necessary research. I built the MS2 to Extra specification with the aim of controlling fuel, spark and idle, although I'm not planning on using the idle control unless I do some crazy stuff to my engine that requires a change in idle speed. My spec was as follows:
- Basic build according to MS2 Extra documentation (link)
- 4 injector drivers on a separate board (link)
- Joe Perezís modified ignition outputs (link), to avoid startup pops and negate the need to unplug the coils when updating firmware.
- Additional opto-isolator for the second CAS input (link)
- MAF input circuit (link)
I also built a JimStim, which I would recommend to everyone attempting a MS build, if only to check your trigger inputs before you get it on a real car.
In case youíre attempting a similar installation yourself, Iíve attached the build document I put together for my MS2. I hope it helps!
A couple of photos of my finished Megasquirt. Not tidy, but functional!
The 4 injector drivers are on the smaller board in the lid of the Megasquirt case. There's provision for 4 ignition drivers too in case I want to go COP at any time. I left the two on-board injector drivers on the main Megasquirt board but they're not used.
The next step is the harness, which is quite a serious undertaking for a parallel install. Hereís a pic of mine as well as the wiring scheme for the DB37 connector. All the pins from the stock ECU are carried through to the harness apart from the 4 injectors and 2 ignition outputs.
The DB15 connector is for the four injector drivers and the 6 wires taped up to the top left of the photo are for the ignition and injector outputs from the stock ECU, which were initially wired through to the big yellow connector instead of the wires from the Megasquirt. I taped them up and left them there, just in case I need to use them again in the future.
If you're making any Megasquirt harness (standalone or parallel) then I'd recommend using DIYAutoTune's wiring bundle as it's good quality and it's very helpful to have the individual wires properly labelled.
Also, thanks to Braineack's all-encompassing Megasquirt build thread (here) for all the connector details and some good tips (clearly his aversion to parallel installs was formed since writing that post!).
Fair enough. I'm certainly not going to argue, as I'm on my first Megasquirt install and it sounds like you've done a few!
Annoyingly I'm not going to be able to find out how good my parallel install is, as my project has been cut short by an imminent move overseas. Frustrating, but I'm glad I got it running smoothly, if not finely tuned.
Could be, Joshua. However, that would require me standing on my head in the footwell getting a nosebleed once a year. In my dreams, I see a switch on the dash labeled "boost" and "inspection". Solder and wire are cheap.