MSefi.com read only forum (Jan.15,2018)

I've been dying to kill off my stock ECU- but keep all the emissions stuff. I need A/C, purge, EGR, and fans. I'm pretty sure that purge is open anytime the engine is on, A/C is a pressure sensor that, for some crazy reason, runs through the ecu to the A/C clutch (a relay would have sufficed, mazda). Fans should be easy. That leaves EGR- it has a position sensor and two valves (vent and vacuum). I would like to make a simple PIC microcontroller thingy to drive it- but how? It should it be inversely propo to throttle, come on above 2000 at operating temp, and close at idle, right? So, I assume that I could make a vacuum based controller, with a PIC and MPX pressure thing, that also gets a "go!" signal from megasquirt at the right RPM and temp. I'll call it MegaTree .

Any other thoughts? Maybe I should just open it all the way above 2,000?

Also, I presume the engine should be lean whilst EGR is open- right?

My best thought would be to get a good understanding of how the EGR system on that car operates now, assuming the stock ECU is still controlling it.
On this car vacuum opens the valve, so I would tee in a vacuum gauge at the EGR valve and go drive. Watch for when the vacuum is allowed and removed. Also is it an on-off switch or is the EGR solenoid controlling the EGR valve using duty cycle?

It looks like the A/C system is ECU controlled for engine load purposes, basically the ECU knows how much load is on the engine and can shut down or limit the A/C compressor based on the ECU inputs, load, speed, temp, etc. From a quick look at the schematics I don't see any reason it couldn't be controlled with a low pressure switch and relay. However I don't know enough to say that for sure - proceed at your own risk

Yeah, the pressure sensor goes off ( no conductance) at high pressure- a relay should do. I think I might wire a dmm in to the position sensor on the EGR, my boost gauge might work as well.

mazda runs the a/c wire through the computer like most modern cars to kill the A/C compressor under high load and / or high rpm. this is to provide the best output and save the compressor. it can also provide a small gas miliage boost.

D'oh, forgot about that. I'm sure megasquirt can do the same thing.

The engine is not lean when the egr is open, but rather rich due to the fact that the gas it is inserting into the combustion chamber is inert or non-flammable. it is already burnt wich offsets the amount of air to fuel resulting in a rich condition.

If it were lean when the egr was on it would defeat the whole purpose of EGR. The whole reason your vehicle has egr is to reduce the temps inside the combustion chamber , if it leaned the mixture it would increase the temps. By having lower temps less noxious emissions are produced and the engine is able to advance timing (while avoiding preignition from high combustion chamber temps) at cruising speeds in order to gain power which in the end will result in better gas mileage if it all works right.

One more purpose (and the first reason why that was devised) of running A/C clutch through the ECU is to delay clutch engage until it sets engine idle speed to higher RPM and opens the idle valve some more to prepare for higher load.

Considering this particular feature, you could actually run it through a relay if you can live with a dip in idle speed when you turn on the A/C. It would really be much nicer to have MS control the clutch, though.

is there any updates on wheather msII can control a/c clucth using option out?