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

First post, so let's see if I can ask this correctly.

I'm using a DIYAutoTune sourced Ms2-v3 board. I attempted the PWM mod for the fast idle.

Removed the two small transistors, jumpered the resistor, and installed the TIP120 per the diagram, along with the flyback diode.

Had some issues with the smallish pad size (or rather, getting the old transister leads out) but everything checked out, no bridging, so I figured easy peezy.


On the car, I always see a 12V at the valve leads, regardless of what I try to do to turn the valve off. Thinking about it more, I thought perhaps this was because the frequency was so high, the meter was never going to see any transitions, and I'd need a scope to really see the output correctly. When I have the valve installed, it doesn't buzz, and acts like it's full open, regardless of how I try to adjust it.

Is there some setting or test program I can use to debug the circuit?

Looking at the circuit diagram, it looks like idle-1 is high when the valve is turned on. Is there a way to toggle that on and off steady state so I can check the circuit out with a volt meter?

I also thought about hooking a speaker up to it so I could hear the state transitions, but would need to do something to handle the power correctly.



I've searched and searched, and will gladly take a hint if this information is already out there.

thanks so much

Test it on a Stim and adjust the CLT knob. First use on-off settings - this will tell you if the hardware is working at its most basic functionality. Then put it into PWM mode and see if you can make the LED change its intensity as you adjust the CLT knob.

Thanks Matt-

I am without a stim unfortunately. I can hook up a pot to the temp sensor input though, and I think get in the ball park of the same functionality.

edit: You do appear to be saying, in On/Off mode, I should be able to toggle to a steady state on the output, and in PWM mode, I'll just see high(er) frequency transitions. That was my assumption earlier as well, and I couldn't get it to turn "off" in on/off mode, even adjusting temp setpoints.


The output circuit is dead simple. And for it to be stuck on, I'd have to have the idle-1 output be stuck high all the time, correct? Is there someplace to check that other than the base of the TIP120? Can I probe something right off the daughterboard?

I found a spare ICV and was able to watch the shutter while I fiddled with settings.

Of course, I bought a scope sometime in the middle of all that so I could watch the control pulse.

Thanks for the help. Time for a beer