Megasquirt your Ski Nautique Pro Boss GT40 project

My 1999 Ski Nautique never had stable idle to begin with and being a barfooter I was also looking for a bit more speed. After troubleshooting and some research I decided to get rid of the old Ford EFI.

I settled on a Megasquirt MX3X to do the job. This required quite some research and I figured I share my findings just in case somebody needs to replace an ECU Computer or is interested in engine tuning.

My starting point is a Ford 5.8 351W GT40 engine with multi point fuel injection and distributor. It uses a Ford TFI ignition system with computer controlled dwell (CCD) for ignition and batch fire for the 8 fuel injectors (fires 4 injectors at ones)

I planned a step by step conversion as follows:

1. Add 2 O2 sensors, without tuning is nearly impossible Done this, Also showed me the reason for the unstable idle way to lean around 15 AFR

2. Assemble and test the MX3X, my background is in electronics so I’m good with a soldering iron. Took about 20h to complete.

3. Build adapter to Ford 60pin to MX3X, done I used a junk yard CPU to get the connector

4.Test MX3X and start tuning, this was somehow easy and took me about 10h to get the engine start, warm up and idle stable. This already fixed the Idle problem by tuning AFR down to 12 at idle.

5. Convert to sequential fuel injection, had to build a new harness for the fuel injectors, install a crank trigger wheel and a cam sensor (in distributor), but the results are incredible. Tuning it with the sequential fuel injection provided even better idle can now go down to 600 rpm no problem. Unfortunately winter got in the way no drive testing possible.

6. Not done jet, convert from distributer to coil on plug, and change from MAP to MAF

I have collected a good amount of documentation if you interested let me know I can share it in a Dropbox.

phatsat67 wrote: A lot of guys would probably be interested in the cost of that adapter for the 02 sensor to tune carb boats. .

Looks like an ideal part for Duane to machine up!!!

So, it would be super easy now to bolt a blower on top and still have a civilized engine off-load.. right?

here a few more pictures

I contact the guy I got them from and ask for the price of 3 set let see what happens,