As far as I can tell from the MSM engine control system documentation the stock MSM boost solenoid is controlled by PWMing +12V to the solenoid.

Here's the diagram from the documentation:



This is obviously different from some other EBCs out there such as the one sold by DIYAutotune, where you PWM the ground of the solenoid. The boost control circuit on the DIYPNP uses an N-channel FET to drive this, which won't work on the stock EBC since it's already connected to ground.

So will a P-channel FET circuit similar to the one below drive the stock EBC, where a low from the MS turns on the FET and sends +12V to the solenoid?



Also, would I be able to control it by setting the "Output Polarity" in the Boost Control Setting to "Inverted"?

Lee

 

Seems more likely at its just a mistake in the manual and it runs like every other solenoid, with pwm on the ground side.

 

I don't think it's a mistake. It shows up again in a completely different document saying the same thing.

 

As far as I know, it doesn't opperate like ebc. It just keeps the wastegate closed until ~3500rpm.

 

Not a mistake (unless, of course, you wish to make the case that everything about the stock MSM engine management was a mistake, and you've have a point). The Mazdaspeed solenoid for some reason uses a high side driver, and just runs in an on/off fashion.

 

So, assuming I add a high-side driver to the DIYPNP, how do I control it? Do I just use a generic output? Do I turn it on at 3500RPM like curly says and what do I do to turn it off?

 

Drive below 3500rpm.

 

It almost sounds easier to just use a MBC & bypass the stock solenoid, or to wire a DIY EBC unit that would give you full control regardless (and a possibly a new/faster solenoid that would respond quicker). The only control I can think you'd achieve is to open at a later rpm for teh max ihi spoolz

 

I suppose I could have it active at 3500 rpm and map < x psi, where x I max safe boost.

 

I'm aware of the other alternatives. I just want to know how the stock boost controller works.

 

Are you trying to raise the stock boost pressure?

 

Do you mean above the stock 8.5? Eventually, yes, but to start, I'd like to keep it the same.

I'm thinking to start by having it off and just go with the wastegate limit to set a baseline, then see if I can increase it. I have a stock MSM so I'm not looking to increase boost much.