MSIII vs Carb
 

Hey guys. I've recently built a N/A 6P Bridgeport. Ive started the motor on the stock ecu an as we all know bridges don't like the stock ecu's. I knew it was going to need either a standalone or a carb. I would like to know from the MSIII users how they like it and what I should expect if I decide to go that route. Is it as plug and play as the other standalone units?

ms3 its very straight forward no mods need to run a wankel engine like any standalone if you wire everything right you should start the car in no time.

.

If you can go MS3 than go, more control over the engine.

You also will have more fun with tuning, with more options if you want
to control other stuff.

I give up carb to go MS3, the best thing i have done, now i´m preparing
a N/A 6P that will go turbo using the same ECU.

How does the ignition get run. I heard there's 2 VR's on the MSIII one on the actual main board and another on the extra? I'm a little confused on that part. Also the shielded wire? I would get the harness that MS has. Is it labeled or am I on my own for that? I love carbs. But I like the possibility of being able to turn with possible mods later on such as a turbo or supercharger. Fuel pump gets wired to the ECU as well I'm assuming? Also do you still need the BAC to run the MS?

First, there is no comparison between a good EFI system (whether it be MegaSquirt, Haltech, etc.) and a carburetor. EFI is an improvement in every way possible. Especially with high overlap large port area engines like bridgeports (6 port?). With EFI you can build a car with ports like that which is actually tolerable to drive.

For example, the ability to tune the light load no-vacuum areas in Alpha-N and then switching to a speed density table in boost.

MS3 requires a lot fewer changes to run the rotary than previous versions.

If you get a pre-assembled MS3 w/ 3.57 main board and MS3X ( MegaSquirt-III EMS System with MS3X Expansion V3.57 - Assembled DIYAutoTune.com ) then you don't need to perform any mods. Just pop open the case, set 3 jumpers, turn 4 pots all the way counterclockwise and then put the case back on.

There are two wiring harnesses; one which connects to the mainboard and one which connects to the MS3X board. If your MS3X harness doesn't have the shielded VR ("cam") wire then you'll have to add it but at this point, I believe most vendors (definitely DIYAutoTune) have moved to the shielded wire. It's really not a huge deal to add it anyway if necessary.

Far as I know, all vendors label their harnesses (example: 12' MegaSquirt Wiring Harness (MS1 / MS2 / MS3 Ready) DIYAutoTune.com) and there are instructions on how to connect the rotary specific connections on the DIYAutoTune site:
How to MegaSquirt your FC RX-7

Checking the MS3 wiring diagram will give you a lot of info about what can or does get connected to the ECU:
Megasquirt-3 MS3 Hardware Manual

The BAC valve isn't required, but highly recommended so that the ECU can control the idle. With a Bridgeport you really won't have much luck running closed loop idle via the BAC but it can still be used for things like warmup idle, fan idle up, etc.

If you don't even want to open up the ECU and instead want something out of the box and ready to go, take a look at the MS3-Pro. It's a fully optioned out MS3X sold as a package with tuning software, harnesses, a great manual and support. DIYAutoTune has improved the VR conditioners so there are no jumpers nor ports to set, the harnesses are connected with Ampseal connectors and the plastic case is fully sealed.

The video below covers the MegaSquirt MS3-Pro install on my '76 Cosmo from start to finish. Everything is shown including making up the ECU/fuse/relay panel, laying out the harnesses, making all the connections, proper soldering and crimpting technique, using WeatherPack connectors and finally firing the whole system up in test mode to verify it all works. Wiring up an MS3-Pro is basically the same as an MS3X, the only difference being that MS3-Pro uses more generic names for some of the wires. This video is a great overview of the process of installing any standalone and should answer a number of questions for the standalone beginner.

Aaron, thanks for the response. I think I will be going with the MSIII. The pro is a little out of my price range. You mentioned that I need to open the case and make 3 jumpers and move 4 pots. I haven't looked yet bit I'm going to assume this is shown in a manual or on DIYautotune? If not where would I be able to find the info to be able to do it. As this would be my first complete standalone install and I would hate to mess up the squirt my first time. Also would I need to mess with the MSx at all?

considering how much a good carb is, just go Megasquirt. I've used both (well MS2 for a long time) and while carb is "simple" it also is only good a one point. The rest is compromise.

The link I provided to the DIYAutoTune FC MegaSquirt writeup has instructions for setting the jumpers.

Definitely read through my writeup then. It covers MS1 and MS2 currently (MS3 coming soon) but will give you a great overview of the process. It's all really the same except you don't need to mod the MS3 and there are a few more injector connections to make with MS3.

If you check the link I provided to the assembled MS3, you will see it includes the MS3X board. The MS3X board contains all the extra I/O hardware needed for sequential injection, 2nd VR input, idle, boost, nitrous, tach, PWM, etc. There isn't much point to running MS3 without the Expander (MS3X) board.

A bit of advice:

In my experience, getting a good signal from the CAS can be a challenge. Grounding things properly and wiring the CAS with good shielded cable are musts.

The MS3 Pro has a much better circuit for converting the CAS signal into something the MS3 processor can understand than the standard MS3. Without going into details, I've had at least 2 RX7's I've worked on personally which had their grounds and CAS wiring set up correctly which still had trouble starting on the standard MS3 due to some kind of interference from the starter. I installed the circuit from the ms3pro into the MS3 and the problems went away.

Ken

I've decided to go ahead and get the MS3 3 W/Extra. Here is my shopping list. Am I missing anything?

I've looked at the PRO and I don't think I need it. I think the 3 W/extra will do just fine for what I have. Aaron thanks for always giving input and helping out as much as you do.