IAC tuning. Am I crazy? (Solved!)

JSC · Post by **JSC** » Sat Apr 22, 2006 12:45 pm

Well, the phasing looks good, looks like your step size is 2.5 ms. Was the waveform of the IAC motor extending or retracting? Did you check it going the other direction?

Scott

bluetrepidation · Post by **bluetrepidation** » Sat Apr 22, 2006 4:39 pm

2.5 is correct... this was retracting only. Same with the other waveforms. I never tested the other direction. If I get time tomorrow I'll change those components and see if my output is any better. I will not be changing the whole chip yet. Didn't come in the mail.

A.J.

bluetrepidation · Post by **bluetrepidation** » Sun Apr 23, 2006 2:22 pm

The plot thickens......

OK I just got done making those changes. I removed the jumpers and replaced the necessary components. Note, I have not changed the chip as of yet. Now I am still getting the same half step waveform as before. But with the jumpers removed I noticed something after the motor has stopped moving. I have my start step size set to 250. As you can see the chip is pulsing the one phase to control current. (Same phase that is half stepping.) After about 30 seconds the chip just drops off the voltage to zero. Interestingly enough if I increase the start step by 1 this does not occur till I get to 254 start steps. So for now this could be a software issue or maybe this could be a capacitance issue where the high start currents are tripping something in which Rc and Cc time delay need to be installed? More the latter considering JSC's bench setup works so well.

A.J.

JSC · Post by **JSC** » Sun Apr 23, 2006 4:10 pm

A.J.

The phase that is pulsing doesn't appear to be current control to me because the current control pulse width should be 46us with the components we installed. The pulsing of the "green" phase when it should be at -12v and the half stepping on the "green" phase indicates to me that your 2916 has a problem. I don't have a clue why the number of steps make a difference. The only other suggestion I have is to check the phase inputs while the "green" output is pulsing. The "green" output seems to be pulsing about 2.5 ms (your step size). Wish I could pull these waveforms off mine to compare (later this week I will) Hang in there, we'll get this figured out.

Scott

bluetrepidation · Post by **bluetrepidation** » Sun Apr 23, 2006 5:50 pm

Alright sounds good. At least we're getting some good info. I have two fresh chips on the way. Let me know when you get your scope.

A.J.

bluetrepidation · Post by **bluetrepidation** » Mon Apr 24, 2006 5:47 pm

I emailed Allegro just to see if I could get some info and here is their responce:

"Hi Albert,

One thing I noticed on the schematic is the RC component values are well out of the recommended range. The R should be 20K to 100K and the C should be 100pf to 1000pf. Anything outside of these values will cause the part, NOT to Current regulate. This may have been the issue. Attached is a demo bd schematic for you reference.

Regards,
Brian J. Atteridge
Field Applications Engineer
Northeast & Canada
Allegro MicroSystems Inc
28 O'Donnell Ave
Shrewsbury, MA 01545
Office - 508-842-8999
Cell - 508-981-5434
batteridge@allegromicro.com"

bluetrepidation · Post by **bluetrepidation** » Tue Apr 25, 2006 3:28 pm

Just replaced my chip. Had no effect on the output. Idle still isn't anywhere near controllable where I can drive the car without fiddling with the laptop.

A.J.

Joethemechanic · Post by **Joethemechanic** » Tue Apr 25, 2006 10:48 pm

My 2 cents.

I am running a GM TBI with the square IAC, always moving, and the MS settings are default, closed position is 200, and 80% of the time it seems to work fine. If the engine trys to stall while tuning sometimes the idle stays high. Haven't had it running long enough to say for sure.

One thing I would like to see is a dashpot effect, even if it just engauges the hot start mode , and tapers down just like the start position, this would be a HUGE benifit.

rapid accell-decell on mine will almost guarantee a stall

Joe

BottleFed70 · Post by **BottleFed70** » Tue Apr 25, 2006 10:53 pm

I'm also having the exact same problems as you guys.

GM IAC seems to work fine if moving in large steps, but small steps is another story. Hot start works fine, cold start and I'll end up with too high of an idle.

Let me know if you want me to try anything. So far all I've done is jumpered the 2 resistors...this seemed to help but it's still not good enough.

Philip Lochner · Post by **Philip Lochner** » Wed Apr 26, 2006 5:09 am

bluetrepidation wrote:Just Idle still isn't anywhere near controllable where I can drive the car without fiddling with the laptop.

A.J.

AJ, this might sound like an odd question but do you have MT configured for Celcius or Fahrenheit?

The reason I'm asking is that I'm running with Celcius and I've noticed that on the warm-up enrichment page the coloured blocks and the black arrow track the bins as if they were in F and not C in my case. I'm wondering if this same issue does not affect the IAC behaviour. I posted to this effect on the Megatune forum but have not received any replies.

If you're using F, I doubt if this would be the issue...

Another thought: Are you sure your IAC is not "sticky" with oil residue. If its sticky, I can imagine it working seemingly OK when receiving multiple pulses (ie having to go somewhere) where the first pulses "rattles it loose" and the subsequent ones keep it going but when receiving single or few pulses, it might stick thus not moving at all or less than instructed. Again, more likely to occur when cold than when warm. I cleaned mine thoroughly with carb cleaner and then doused it with Q20 and it does seem more co-operative now.

Thirdly, did you check with your datalog that MS-2 at least THINKS its doing the right things with IAC?