The Mega Experiment: Part II – Executing the Plan

As the saying goes: Proper planning prevents piss poor performance. I loaded the .pdf for the MegaSquirt, the LC-1 Wideband, and the Dodge Shop Manual onto my tablet. I printed out the pin reference for all of the engine connectors, and I had various diagrams for the alternator, auto shutdown relay, and of course the MegaSquirt and MS3X.

I ordered an MS3 with the MS3X expansion board from SymTech Labs. If you go this route – I was a little confused as MegaSquirt also has a version 3.0 board. So you have a MegaSquirt 3 processor with a version 3.0 board and an MS3X – lots of M S and 3’s to confuse you. I initially thought the 3.0 board WAS the MS3X… (wrong) Then there is the MS3-Pro, which is basically an MS3 + MS3X + some extras – in a more compact case for more money. As of 2013 this is the newest version of MegaSquirt hardware you can buy.

The MS3X expansion board allows you to do all the cool stuff out of the box like launch control, boost, nitrous, sequential fueling, etc. Full sequential is where you can individually trigger the fuel injector on one cylinder for just that particular intake stroke. Common MegaSquirt setup does a “batch fire” where 2 injectors are opened at the same time. This is okay at full throttle as the time it takes for the fuel to travel down the head, it was already on the next intake stroke at 6,000-RPMs. At idle though you are just spraying fuel onto a closed valve every other time at 700-RPM. Not very good for economy and not that great for a steady idle. In order for it to work though, the MS3X needs to know where your camshaft is.

I made a list of all the things I needed to tap into and organized it into a wiring guide for myself. I suggest you do the same for YOUR car – as having 1 sheet to reference in the engine bay was useful.

Some tips: Getting a color correct and marked wiring harness is totally worth it. Not having 50 single color wires going to your ECU makes finding things easy. Don’t assume that just because you have a wire for it, that its connected. The tacho out, PWM Idle, and a few others require circuits to be built in order for them to be used with the stock MS3. The good news is the MS3X had the circuits I needed ready to go. Also, the firing sequence is built into your harness! Not the software, not the circuit, your harness. So if your motor is 1-3-4-2, you need to wire A to cylinder 1, B to cylinder 3, etc.

I searched for about 2+ hours for the connectors and receptacles for the NGC Chrysler PCM. If you have ANY kind of part number or idea of where we can order just the connector it would be awesome! Alas, the closest I got was an AEM Patch Harness for the SRT-4. At $230+ It’s just a little too rich for me. Plus I only need half of it – and to cut it apart and re-splice it without pins… I might as well hack up a stock PCM. ๐Ÿ™ I decided to just splice into the stock body harness and pin connectors after testing.

I carefully laid the engine harness open and took my time (probably about 6 hours) splicing in each wire. Ground was soldered up to one lug and connected right on the back of the head. Routing wires in and out of the firewall was made easier with a small section of oil resistant flexible electrical conduit. I didn’t cut any of the 20 or so extra wires when I was done until after I got the car started and idling. This worked out as I had to send idle control from the MS3X and NOT the MS3. I used Nitrous 1 to control the fan relay and eventually Nitrous 2 will control the A/C. ๐Ÿ˜€

rs232-bt-moduleThe MS3 comes with USB and the old standby: RS232 Serial. I stumbled upon this great hack to use that serial connection as a wireless bluetooth connection for the MegaSquirt. Check out omgpham – bluetooth-x-megasquirt I found the same kit on Ebay for $12, programmed it, and it works great!

Before starting you need to know you have control of everything. TunerStudio has test modes that allow you to fire the injectors, switch outputs, and spark the coil pack. You need to calibrate your wideband O2 (You want this if you want any hope of tuning this yourself.) and triple check your wiring.

tooth_logWhen I turned the key for the first time the fuel pump whirred up (like it ALWAYS does) for 2 seconds and stopped. It was only after thinking about that did I realize that the stock PCM was sitting in a pile under my workbench. Small satisfaction right there that tells you you have a lot of stuff wired correctly. My first attempts to start it were unsuccessful, so I had to do some troubleshooting. This is where the portable oscilloscope came in handy. TunerStudio also has a tooth logger that helps in these situations. With some quick help from the community I discovered that I needed to set a “36-2+2” crankshaft pattern VS. the “Neon 420A” pattern. The next night it started! WooHoo! ๐Ÿ˜€

Another patience test was getting the Idle Air Control (IAC) working. On older cars this is a push and pull device with two sets of coils and some rudimentary “absolute positioning” that can be wired to the MS3. On newer cars it’s a two wire solenoid that opens a little or a lot based on the duty cycle of a PWM circuit. It does this at 500Hz and getting it moving with only 5V is kind of amazing. Amazing because it really takes 12V and I had wired it to PWM Idle from the MS3 where the circuit was not setup to do this. After some wacky idle settings (like 100% open 60% closed) it was starting to get finicky and not open at all. I checked voltage at 100% open and my eyes bulged when I saw only 4.8 volts. Turns out I used “PWM Idle” instad of “Idle” from the MS3X.

For a few days of testing I got away with my battery charger and no alternator power. When the running voltage dips under 11 you start to get away from ideal sensor readings and the MegaSquirt is changing the latency time of the fuel injectors pretty heavily. It runs fine which is a testament to how mature this product is, but it really should have 3 more volts. I went down to the auto parts store and picked up a Voltage Regulator BWD #R296 / Connector #PT173. I soon discovered that the 2003+ Dodge Neon alternator is wired up opposite to all 1995-2002 Neons. Normally 12V is provided and the difference in voltage from the regulator makes it charge. In this car – the field coil is grounded. ๐Ÿ™ So I directly shorted out a $14 voltage regulator trying to save as much of the stock wiring as possible… and back to the store for another regulator. UPDATE 5/2014: Here’s what the wiring for the alternator should look like.

At this point I started to drive it around. I was able to get some good AFR numbers with the stock map from SymTech and my first wide open throttle test yielded some good data: Note the two white slopes below (RPM and Vehicle Speed) and the fuzzy red AFR line holding at 13.2!


Next Up: Android gauges and exploring complete and total engine control.