No Success with GM IAC

[mobythevan]

On several different occasions I have tried to get the GM IAC to work on my 5.3 engine.  The IAC is actually off an LS1, I am using the entire TB and intake from an LS1.  I think I have tested and checked everything multiple times with no luck.  

 

Hardware is MS3 on V3.0 PCB with MS3X card.

 

Behavior:  Power up MS3 and sometimes the plunger extends, other times it retracts.  It never does what it is suppose to (extend to close the airflow) all the time, or even 4 times in a row.

 

I tried multiple IAC motors.  I tried all possible ways of wiring.  I tried various step sizes, various start values, various minimum steps.  Also tried the different modes always on, moving only, etc.  Tested the IAC in a housing and out of the housing. 

 

One step further, I can control the GM IAC motor using an arduino and a polulu stepper driver and the motor works exactly as I expect.

 

I'm out of ideas.  I have also never been able to come across anyone who says they have a GM IAC working and working reliably.  If you do have one working reliably can you please post your settings.

[Jesse OBrien]

I can't offer first-hand experience, but isn't that just a basic stepper motor? I don't know how you've been testing it or what motors you've worked with specifically, but I imagine you'd want to start by measuring open and closed steps (sounds like you've done this, based on the arduino-controlled results), and measure the output MS is providing. Evan went through it in a pretty straightforward way.

 

 

I'm trying not to make any assumptions as to what you've done and what you haven't done, but I'd be interested to see your known-good measurements as to what actuates the IAC to open/closed as compared to equivalent MS outputs on whatever configurations you've tested.

[Matt Cramer]

I have one working on a 4.8 powered pickup - same throttle body as a 5.3 - with an MS3-Pro. I'll see if I can get the settings posted soon. In the meantime, here are some notes on troubleshooting steppers:

 

Preliminary settings

First, make sure that the idle control is set to one of the stepper output modes, not PWM or on/off idle control. For initial testing, we recommend using open loop instead of one of the closed loop modes. Closed loop requires more complicated settings and has more that can potentially go wrong.

The time step size is how long the stepper driver will command an individual step. If the valve is perfectly dialed in, this will match the time it takes the coil move the motor through a single step. If this value is too low, the step is not completed, and the valve does not move. If the step is too high, the valve will move more slowly than it can - but otherwise there aren't any consequences. Your best bet is to set this for 10 ms, then decrease until the valve no longer moves. Then add 0.5 to 1.0 ms.

4 wire valves that turn freely usually need to use "Always On" mode. Valves that are difficult to spin by hand usually need to use "Moving Only" mode; the same goes for all 5 or 6 wire valves.

The start value needs to be set to a large enough value that the valve retracts fully from any position the valve can reach during operation.

Now, on to troubleshooting specific problems.

Problem: Valve vibrates when commanded to move, but does not actually turn.

One coil is wired backwards; swap wire 1A for 1B, or 2A for 2B.

Problem: Valve moves, but in opposite direction of intended.

Both coils are wired backwards. Switch wires 1A for 1B, and 2A for 2B.

Problem: Valve does not move at all on initial power up.

One possibility is incorrect wiring. Make sure 1A and 1B are on one coil, and 2A and 2B are on the opposite coil.

The other usual problem is the step size is set too small. Try increasing it and see if the valve moves.

Problem: Idle speed is not consistent from one start to another at the same temperature.

Usually, this is caused by the start value being set too low. Increase this value until the valve retracts fully.

Problem: The valve retracts normally, but then appears to stop working at some point during operation.

First, check to be sure the algorithm is not set to "15 minute IAC"; this will switch the IAC valve operation mode after 15 minutes, and is only used with a few specific valves that behave differently when warmed up.

Next, try increasing the time step size and/or minimum number of steps to move. Some older valves can have problems with stiction. Increasing the time step size will send a longer pulse, while increasing the minimum number of steps to move will send more pulses that can un-stick a stubborn valve.

Problem: Idle speed hunts while the number of steps displayed is constant.

It's easy to assume the IAC valve is responsible here. After all, it's supposed to control the idle speed, and the idle speed is behaving wrong. However, this is likely to be an issue with the ignition timing or fueling instead. See section 6.5 of the MS3-Pro manual for idle tuning.

[mobythevan]

In regard to the video you linked, this is one of the things that is confusing to me about IAC control.  This video seems to be using standard megasquirt and not extra code.  In extra code the plunger closes off the airflow during homing.  That is how it is explained in the extra forum by James.  However, in this video, Evan explains that homing mode opens the airflow.  

 

Do you know if Evan uses standard megasquirt or extra code? 

 

Evan went through it in a pretty straightforward way.

 

 

 

[Jesse OBrien]

In regard to the video you linked, this is one of the things that is confusing to me about IAC control.  This video seems to be using standard megasquirt and not extra code.  In extra code the plunger closes off the airflow during homing.  That is how it is explained in the extra forum by James.  However, in this video, Evan explains that homing mode opens the airflow.  

 

Do you know if Evan uses standard megasquirt or extra code? 

I don't, sorry. I wasn't even aware that the extra code controls IAC differently than the standard code does. I've already contributed as much as I can to this, my inexperience with IAC and with extra would keep me from giving anything else worthwhile. I'm still working on getting my MS3 wiring wrapped up.

[Matt Cramer]

The latest MS3 code (just released earlier this week) allows you to specify if the homing position is closed or open.

[mobythevan]

The latest MS3 code (just released earlier this week) allows you to specify if the homing position is closed or open.

 

Thank You Matt