My Quest of Running Flex Fuel on MS3+MS3x
 

<p>This has been touched upon recently in a couple other threads so I am going to make a central thread where I document my process of setting up flex fuel on my home built MS3+MS3x. The process should be quite similar on MS3Pro, and MSLabs MS3s. You peasants with MS2's I can't help you. The goal is that by the end of this I will have a shopping list that anyone can go purchase and run flex fuel with their megasquirt.</p><p>Parts I've acquired so far if you want to follow along:</p><p>GT500 600cc injectors</p><p>DW200 Fuel Pump</p><p>GM Flex Fuel sensor&nbsp;(there are multiple to choose from, see this link for more info about the current cheap ones)</p><p>Sensor Harness</p><p>Ricey Badge&nbsp;(Optional)</p><p>I have done quite a bit of reading, and have contacted DIY autotune for some base maps. As far as I can tell I'm going to wire the flex fuel sensor into the Flex Input on my MS3x and then that should give me ethanol percentage. Everything after that is going to be tuning, and I will figure that out in the future.</p><p>Two Miatas that I have seen mentioned running flex fuel are <span>@AbeFM and DIYs Miata,&nbsp;</span><span>@Matt Cramer and <span>@Ben, any input is greatly appreciated. Attached is the basemap that DIY sent me from their miata running flex fuel.</span></span></p><p>&nbsp;</p>

Awesome will be watching this and asking dumb questions.

<p></p><p>As will I.</p>

https://www.miataturbo.net/attachmen...ine=1436205463

This is what Demitrios provided for the addition of flex sensor to ms3 basic. Just throwing it in the bowl, if its not common.
...

The flex input should already have a pull up on the ms3 card. I need to go read again.

This went with the picture, might help...

"This is what you need to do to enable Flex Fuel.
The port to use for flex fuel with this modification done is "PE0".

--
Dimitris Stasinopoulos
MS Labs - Automotive Electronic Solutions"

That makes sense. PE0 is a different pin than Flex.

Wait. It might be the same. Damn I wish the schematics were open source.

In4dumbquestions.

Also, nice choice of injectors :party:

Had to throw in a shout out.

Flex fuel compatability became a standard feature on the MS3 Basic at some point. I know all the boxes I've sold have had it set up as standard (i.e. no internal mods required).

My unit is an early 2014 and needs the internal mod from talking to Demitrios. Im looking forward to this flex sensor build but i'm holding off adding e85 until my motor is built, when the DP goes on i will already be close to the rods torque safety limit.

<p><span>@Reverant could you clarify when it became a standard feature and what the wiring is to PE0?</span></p>

01-05: 3.0c and higher
99-00: 3.1 and higher
96-97: 3.1 and higher
94-95: 3.0a and higher
90-93: 3.0a and higher

The suggested modification above means that you will need to connect the 2 resistors to the sensor and the MS3 board as shown, then route the wire to the ECU through any unused pin on the DB37.

What is the point of the resistors.

To make it work. :)

Yes but why, I thought the ms3 card had built in pull up resistors on the flex input.

The FLEX input on the earlier boxes was used for the VSS input instead. So instead of using the FLEX input for flex fuel, PE0 is used instead, and that one doesn't have the resistors.

Awesome.

How'd it go? I had lots of issues early on, something in the code would lose count, and it'd think my fuel temp was -40* C or something ridiculous. Anyway, it would go full rich to compensate just once in a while, whole car bucked. I complained, I assume some smoothing was done in software. Worth being aware of. :-)