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

I am having a problem with my IAC motor that I am trying to sort out. The IAC motor acts very sporatic, sometimes it moves a little, sometimes it just buzzes, and sometimes it does nothing. I have it wired up exactly as the wiring diagram from DIYAutoTune shows (I am using their harness). I have read that these symptoms can be caused by the wiring to the IAC not hooked up properly, but before I start moving wires around, contrary to the wiring diagram, I want to make sure that my V3 board is assembled correctly.

I have wired my IAC stepper motor per step 22 of the MegaSquirt assembly manual, it says to jumper S12C to JS9(+12v). The JS0-JS3 jumpers are correctly installed also.

I checked the wiring and schematics section to verify this, and it indicated that the JS10 should be jumpered to IGN as the power supply for the IAC.

I have JS10 jumpered to IGBTIN per step 65 of the assembly manual for my MSD6 ignition box.

Can anyone shed some light on this? I just want to make sure that I have correctly wired my V3 board, before I continue with further IAC diagnosis. Thanks.

Blown87,

Some IAC, though appernetly identical, are wired differently. We have certainly seen this on the in-line pin units. So you have to check them. There's instructions here: http://www.megasquirt.info/ms2/IAC.htm

On a V3.0 main board you need to jumper:

- (1A)JS0 (under the processor socket) to IAC1A (near the DB37 connector) - this goes to Coil 1, lead A on DB37 pin 25

- (1B)JS1 (under the processor socket) to IAC1B (near the DB37 connector) - this goes to Coil 1, lead B on DB37 pin 27

- (2A)JS2 (under the processor socket) to IAC2A (near the DB37 connector) - this goes to Coil 2, lead A on DB37 pin 29

- (2B)JS3 (under the processor socket) to IAC2B (near the DB37 connector) - this goes to Coil 2, lead B on DB37 pin 31

- Install a jumper from the hole marked S12C to the hole marked JS9 (+12C)

So it sounds to me like you have the jumpers right. You might need some adjustment because the power resistor values may not be quite low enough for your application. This could cause sporadic problems.

To see if this is the problem, cut the leads off a resistor or use a small piece of wire and solder it across the two power resistors on the bottom of the MegaSquirt-II board. These are the two large brown units on the BOTTOM of the board, on the end opposite the side of the board with the 2x3 pin header. These have large solder pads on each side - just jumper across each one so you get 0 Ohms and see if this improves operation. This is very likely to be the problem for those who see the proper step commands given in software but inconsistent response from the motor.

The resistors are for protection against shorted wiring. If you short the wiring to your stepper motor you could burn out the stepper chip, as you could many other devices on a car by shorting them. But they are not needed for normal operation and will not reduce the longevity of your stepper motor or of the chip.

Bruce found problems to be due to transient spikes that caused the chip to shutdown even though there was no overcurrent. To eliminate it you need to add a filter circuit to it and tune the circuit for your particular setup using a scope. But we don't feel this additional complexity is worthwhile or necessary.

Lance.

Lance,

Thank you for the fast reply. I soldered the resistors on question. I now get consistent activity. With the key on the IAC pintle extends, during cranking it begins to retract. The engine stalled right away and movement stopped. I believe it is working properly now. My tests were done with the IAC out of the throttle body. I assume that during cranking what I was seeing was it moving to the set cranking position. Is the extension with key on /engine off normal?
I should have specified in my original post that this is a square connector GM IAC motor.

Blown87,

It sounds like you are making progress. Normally, on powering up MegaSquirt, the IAC pintle should retract towards the stepper itself, then extend once the engine begins running.

So you might have the wires the wrong way around (regardless of the instructions - there may be differences in some steppers). In that case, you should reverse the wires so that the wires originally connected to:

- Coil 1, lead A is now connected to Coil 2, lead B,
- Coil 1, lead B is now connected to Coil 2, lead A,
- Coil 2, lead A is now connected to Coil 1, lead B,
- Coil 2, lead B is now connected to Coil 1, lead A.

Let us know if that works.

Lance.

Thanks for the clarification. I read in the Idle Control document that the code works as follows: 1) At start up, the motor retracts fully (wide open, fastest idle). This becomes the zero posistion. 2) It then begins to close gradually with coolant temperature.
I was not sure when it said "start up" if that was engine start up or Megasquirt power up. It makes sense now. I will rewire the IAC and see what happens.

Here is an update: I switched the wiring to the IAC as suggested earlier. Now with the key on the IAC pintle retracts. I played with it by running the pintle out by hand and then turning the key on, each time the pintle retracted. Now it seems that I have consistent operation in the proper way! I have not been able to drive the vehicle since I made the repair, but when I do (sometime in the next few days), I'm sure it will work. Lance, thank you again for the help.

What sort of amps does your IAC take? I'm just curious as at the moment i've used 300mA hookup wire on the PCB for the IAC wires, but I have some 7.5A spare that I may use instead.

I have no idea the amperage of my IAC motor. Are you suggesting putting an in-line fuse for protection because of bypassing the resistors on the daughter card?