4 wire GM stepper loosing steps. FIXED! msq on pg. 2

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jesse408
Experienced MS/Extra'er
Posts: 178
Joined: Tue May 14, 2013 6:30 am

Re: 4 wire GM stepper loosing steps.

Post by jesse408 »

Listen guys, I really appreciate your willingness to help but I think I may have figured out something...maybe not.
A few weeks back my alternator went out and I remember seeing a data log of my voltage spiking over 18 volts for a few miles as I limped the car back home. Maybe the high voltage fried something. Is it possible for the IAC coils to ohm out within spec yet be bad? Maybe damaged the driver?
jesse408
Experienced MS/Extra'er
Posts: 178
Joined: Tue May 14, 2013 6:30 am

Re: 4 wire GM stepper loosing steps.

Post by jesse408 »

Just for my own information- to see what would happen, I connected the stimulator and changed my closed loop "valve closed" steps from zero to 20 and simulated a slightly high idle, and the idle steps did not attempt to go any lower than 20 to compensate for high idle.
I then changed it to 30 and the steps didn't go below 30 to compensate for high idle.
When set to zero, same thing.
It was mentioned that fully closing the valve should be avoided to keep it from getting stuck. I just tested the fit of the pintle, and my IAC doesn't even come close to sticking so no worries there.
As far as closing the valve, the valve NEEDS to close, correct? Isn't that what Homing is for at key on. When we say 150 steps, we are saying 150 steps open from home, correct? Isn't this how TS calculates stepper position? Home is closed AKA, no airflow.
billr
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Re: 4 wire GM stepper loosing steps.

Post by billr »

"I just tested the fit of the pintle"

What are you referring to there? Surely the pintle/poppet won't go all the way through the seat hole, will it??? The pintle has to mechanically contact the seat to home "closed". If it can't, you would have to home "open" so that the pintle hits the internal "retract" limit. Those GM IAC valves come with different size pintles, with all other aspects being the same. Are you sure this is the correct IAC for the TB? I don't think it is likely that the voltage spike hurt either the stepper or drivers, but anything is possible. Is the resistance on the stepper you are using the same as some the other two, that weren't there during the spike? I usually find 50-55 ohms, not sure what the official spec is.
billr
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Posts: 6828
Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Re: 4 wire GM stepper loosing steps.

Post by billr »

I forgot to mention... when it goes closed for "homing" there is usually (always?) no vacuum in the intake, so no real load on the pintle like there is once the engine is running.

It seems like you should plug the IAC inlet port (and turn off IAC control) and focus on getting a stable idle using just the throttle stop. I need to read through some of your recent posts again...
jesse408
Experienced MS/Extra'er
Posts: 178
Joined: Tue May 14, 2013 6:30 am

Re: 4 wire GM stepper loosing steps.

Post by jesse408 »

You are correct. The pintle on this particular model is made from a hard plastic with a 45 degree (or so) seat on it and so it fits exactly like a cylinder head valve and seat. No binding or sticking. Vacuum will attempt to pull the valve open in this situation, a backfire would attempt to close it.
I did quite a bit more messing around and in test mode and the valve seems to work correctly.
I looked at some msq's of similar throttle body setups, and noticed some major differences between my settings and their settings. 2 of the setups I looked at with LS1 style throttle bodies like mine (on the Sloppy Mechanics Wiki page), home the valve OPEN instead of CLOSED, so maybe that is worth trying...although I am unsure how they wired their valve?
Last edited by jesse408 on Wed Jan 27, 2016 12:00 pm, edited 1 time in total.
jesse408
Experienced MS/Extra'er
Posts: 178
Joined: Tue May 14, 2013 6:30 am

Re: 4 wire GM stepper loosing steps.

Post by jesse408 »

Okay guys I just changed my IAC settings.
Homing the valve OPEN was the key.
I have not taken a data log of what is going on, but I can assure you that the idle reliability is WAY more reliable now than it has been in a very, very long time.
Thanks for putting up with my stubbornness guys!
Last edited by jesse408 on Wed Jan 27, 2016 11:56 am, edited 1 time in total.
jesse408
Experienced MS/Extra'er
Posts: 178
Joined: Tue May 14, 2013 6:30 am

Re: 4 wire GM stepper loosing steps.

Post by jesse408 »

Here is the new msq that is working very well so far.
I hope this helps someone.
I cannot take credit for the settings. Matt Happel's tunes on the Sloppy Wiki page had these settings and they worked nicely.
Thanks, Matt!
OPEN IAC tune.msq
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