I turned on IAC1 and IAC2 one after the other from the Output Test page and found no voltage between the A and B pins for each corresponding IAC. Checked for continuity for all the 4 wires. And finally to eliminate all doubts I tested at the pins directly but yet no voltage.
This is a new MS3Pro that I've just installed. Our initial plan was to run without IAC but since we can't get it to idle we thought it would be a good idea to have it installed. Before we removed the block off plate I thought I would do the wiring first and encountered this problem. According to the above support page it says:
If it does not respond (and you don’t have any configuration error messages indicating you’ve accidentally enabled the stepper output twice), it is most likely that the stepper IAC driver chip is damaged.
Can I check for any specific resistance across the iac pins to confirm if the chip is intact or toasted? If yes, please let me know what should i be looking for between which pins.
You don't have IAC drive enabled in that MSQ. I'm not sure if it is even possible to test those outputs that way.
The stepper chip is probably internally protected against over-temp and over-current, so I think it is unlikely it got damaged. I'll have to read some, see if there is a jumper that needs to be set to provide 12V "motor power" to the chip to control.
No, I don't think there is going to be any resistance test for the driver.
My first attempt was to check all the grounds and I tested each pin for continuity with ground. Why does my MS3Pro state pin 13 of the white connector as 'Power Ground' whereas it should be labeled 'Shield Ground' as per the MS3Pro Manual.
I had the IAC enabled first while doing the output test then I read in the manual to disable the IAC so that you could assign them as aux outputs activated by TPS for testing purposes. But as what I understand is that OUTPUT TEST overrides any configuration assigned for that particular so it doesn't matter if it is on or not. I didn't perform the home/run position tests - which I assume would require the idle to be defined. I'm doing a raw output test to toggle the pin on/off.
Should I consider this device as faulty and look for replacement?
Not yet. Change back to using the IAC as a stepper and post that MSQ. Try testing again in TS IAC "test mode", but also measure voltage from each (IAC) pin to ground. See if any pin is flipping from ground to 12V as the stepper is supposed to be moving.
Tested it (see new tune file) as instructed. No pins are showing either 12V or ground. Tested with a test light, voltmeter, you name it. When I switch of the ignition the pin sinks to ground causing the tester to glow. Soon as I open the switch it's off again.
Should these testing be done with the IAC connected? It should work without the IAC right? I mean is there some kind of circuitry that kills power if no current is drawn or something like that?
If needed, I can connect the IAC and splice the wires (which I don't want to) for testing
No, the stepper does not need to be connected to see voltages at the driver. It connects each wire to either ground or 12V; no "pull up/down" load is needed.
I recommend "always on" for the current, or at least "holding". Those give more positive control of the stepper. "Moving" is a crutch to prevent mismatched steppers from overheating, rarely do you need to resort to it.
DIYAUTOTUNE has confirmed that the chip is faulty and have asked me to send it in for repair. I'm sending them the Serial number to see if it's still under warranty. I'm sure it is a we have bought it less than 6 months ago.
billr wrote:I gotta ask DIY (Matt C)... Is there a known chronic problem with the Pro stepper-driver circuit?
It's not all that common compared to the number of MS3Pros in the field. But the stepper driver is loaded to a higher percent of its maximum current than most other drivers are, and some settings run it at 100% duty cycle on top of that, so it one of the more stressed components of the ECU. We've made a few tweaks in current production to improve its longevity.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
What makes me so amazed is that I didn't even connect the IAC before it failed on me. I popped open the rear cover and inspected the U3 chip which is the stepper chip and didn't find any burnt tracks or issues with the soldering. What I like about megasquirt is their unbeatable support that no other company can beat.