I have read over a few great threads of people getting MS controlling fuel and spark. However, I would like to install Megasquirt as a complete replacement for the stock ecu. There are a number of functions, like AC, radiator Fan, and some sort of PS function that the stock ecu deals with.

Does anyone know of an MS install that completely replaced the stock ecu and maintained those functionalities in their car?

Thanks for the help,
Justin

 

When are you getting back in town Justin? I think we may be able to work this out together if you still want too. I'll have to find some free time which is getting tough but we can make it happen and see what we can come up with...


AC idle-up can be wired without the MS getting involved as it uses up an output that can be better put to use to try and involve the ECU. You can use a relay and fast idle valve-- trigger the relay/valve when the compressor comes on (use compressor clutch power to trigger the relay) and you're good to go.

Radiator fan is easy to control. Just use an output from the MS to trigger the stock relay on the fan at a certain temperature. The MS-I with MSnS-E supports this with a minor circuit addition. http://www.diyautotune.com/tech_arti...#Add_Output_v3 has details on how to implement this, and there is a 'modkit' on my site with the parts needed for just a few $.

The stock ECU controls Power Steering? Any more info on that?

 

On 2001+ models, pin 4C on the stock ECU is the powering steering switch. This switch is pressed when you slightly steer the wheel either way. That way, the ECU knows that it has some slight load added (power steering pump) and so (if at idle) it takes care not to stall.

 

Jerry,
Thanks for the respons. Did not know you were reading this forum. I am definitely still interested in getting your help on this one when I get back. I have just been doing a bit of homework and ran across something I was not sure I understood.

I have most of the pins mapped out for fuel, ignition, and IAC. On the miatas it is only a two wire IAC (not a four) so I don't think it will take up too many needed inputs.

Are you sure that the 1990 ecu does not use the power steering switch as well. I assumed it was some sort of fast idle trigger. There is definitely a switch going to a pin on the ecu (if i had my wiring diagrams handy I would tell you which one) in the wiring diagrams.

Lets hypothetically say there is such a switch. Could I get MS to take that as an input and control Fidle accordingly?

Justin

 

I got a hold of my wiring diagrams this morning and looked up specifically what pin I was thinking of with the PS switch. It appears to me that the switch runs to pin 1P on the ecu connector.

Pin 1R is where the cooling Fan relay comes into the ecu. I think that is where you would trigger the radiator fan from.

Some more pins that I was worried about (due to a lack of knowlege as to their function) were Pins 1S and 1Q. Those pins go to the Heater Control Unit and the A/C thermoswitch respectively.

Since the a/c does not work in my car currently, it would not be the end of the world if my A/C lost functionality due to this. But someday I hope to make my a/c work again... my initial guess was that this switch can cycle the compresson on and off if its load is low (i.e. it is not having to cool much air!)

a heater control unit... um..why is the ecu messing with this? Perhaps it is an input signal to the stock ecu for trouble codes or something?

Justin

 

The MS won't work as a stand alone unless you get 'arty' with some of the more basic connections.

I've tried running my car without the ECU attached and once I jumpered the fuel pump, I still coundn't get it to rev beyond idle. I guess that it is the +5V tps ref signal which isn't too hard to fix, but then there is the fan out put and you would probably find some other outputs from the factory ECU that we wouldn't be able to get working properly because of the limited number of outputs on the DB37 connector.

The MS3 on the other hand will probably be able to do everything on your car and have enough spare connectors to also run your espresso machine....

 

Ok, i did a bit more reading. It does not look like MS takes those switch inputs to trigger fast idle solaniod. None of the MS installs i have done have used a fast idle solanoid at all.

MS seems to just trigger the fast idle based on colant temperature. So at least those two ecu inputs are not needed. (that assumes that the engine does not stall out when you turn on the ac or turn the steeringwheel when idling)

As far as the cooling fan triggering requirments, code versions of MSnS extra can control the fan.

That still leaves the heater control unit pin...

any one know what that one is for?

 

I don't get out here all the time but I drop by from time to time and thought I saw someone familiar here .

What's the issue with the 5v VREF on the TPS? Does the Miata TPS not like that or something?

I'm sure we can do full standalone on these cars, keeping in mind these are ENGINE management systems so they're really not for everyone in the sense that a pure aftermarket EMS really isn't designed for the road at all due to EPA regulations and such. Using it for the road is really illegal then, but if you wanted to take it upon yourself to do so you'd need to either accept that this type of EMS functionality requires either a sacrifice of any non-EMS related functionality, or other ways to accomplish those goals, maybe by leaving the stock ECU around just for that particular feature you're looking for.

It's not to say the MS can't be made to do these things, but coding would be required to repurpose inputs and outputs. This will happen I'm sure but that's where it's at for the moment.

As for why your heater would need to talk to the EMS I can't really help you there .

For the IAC you're right that it's just used for warmup at this time. I'd like to see that changed to support AC idle up or whatever other idle-up needs there may be (putting an auto in drive/reverse?), but that's back to further code development and allocation of I/O for these features. The MS3 will remove the I/O limitations but is a ways off still....