IAC tuning. Am I crazy? (Solved!)

[69 1/2 Six Pack Bee]

For what it's worth, guys, I was using a BRAND SPANKING NEW IAC from GM....and the operation still fell on it's nose.
I think you guys are battling another "gremlin" than a sticky stepper.

[JSC]

A.J.

You said changing the chip had no effect on the output. Is the one output still half stepping? Snafu on the new scope, it won't get here until Friday and I'll be gone this weekend so it'll be next week now before I can do any checking on my end.

Scott

[bluetrepidation]

I don't know if you took time to look at my scope readings but there is defiantly something wrong with the output. I motor isn't sticky. My stock ECU ran fine. This is a 1999 car. Everything worked perfect in stock configuration. Plus I have an extra motor I plug in to test with. Both have the same issues. I am tuning in Celcius though. I'm not paying any attention to what the temperature "is" really I just pay attention to how the temp climbs. I never notices the F in the warm up bins myself. Though I haven't had time to get to that point b/c I want my IAC to work correctly. Last yes I checked my datalogs and I can see on warmup where the IAC should be taking single steps.

I highly doubt at this point and with this many people having the same issue that everyone would be overlooking these things all together. BUT we'll get to the bottom of this! This issue upsets me but not nearly as much as my horrid stock ECU! ;)

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?

[bluetrepidation]

Hang in there guys. Keep tinkering. Keep an eye on this thread. And by all means if you have access to an oscilloscope do try to get some readings for us to look at. I'm really hard headed at this point and want to solve this for all of us.

A.J.

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

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.

[Bernard Fife]

There is one issue I can conceive of that might give IAC issues. If you are using the relay board, it has a polyfuse that limits current to MegaSquirt to 1.1 Amp maximum.

It's possible that some combinations of IACs and MegaSquirt builds will result in the draw climbing above 1.1 Amps (though I have not seen this myself).

If the current does go above 1.1 Amps, it's conceivable (but not overwhelmingly likely) that the current is being limited enough to stall the stepper, but the voltage is staying high enough to keep the processor running.

To test if this is a problem, either jumper the polyfuse (CB2) on the relay board, or replace it with a higher rated polyfuse (like RXE250-ND).

Again, I don't know if this is a likely possibility, but we are running low on things to check.

Lance.

[bluetrepidation]

JSC,

Yes it is still half stepping just like before. OH MAN YOU ARE TEASING ME WITH THIS SCOPE! hehehehe Alright well I'll just haft to wait some more then. I had a brain storm the other night.......

Since phase 2 seems to be operating correctly I was going to lift the phase 1 pin on the chip from the board. Then jumper phase 2 to the floating phase one input pin. Then see if I get a good waveform out of the phase that normally is incorrect. If I get time I'll give it a go.

Also the field engineer at Allegro seems to shoot me useful emails so I'll try and keep him in the loop. This is his latest comment:

"Hi A.J.

It looks like the chip is damaged. Or you have a spike on the phase input that we're not seeing. Please try another an let me know.

Brian"

So I'll get back with him and keep experimenting.

A.J.

A.J.

You said changing the chip had no effect on the output. Is the one output still half stepping? Snafu on the new scope, it won't get here until Friday and I'll be gone this weekend so it'll be next week now before I can do any checking on my end.

Scott

[bluetrepidation]

No relay board here. My Megasquirt II is pulling power from where my stock ECU pulls from. Very little voltage drops during starts as well.

A.J.

There is one issue I can conceive of that might give IAC issues. If you are using the relay board, it has a polyfuse that limits current to MegaSquirt to 1.1 Amp maximum.

It's possible that some combinations of IACs and MegaSquirt builds will result in the draw climbing above 1.1 Amps (though I have not seen this myself).

If the current does go above 1.1 Amps, it's conceivable (but not overwhelmingly likely) that the current is being limited enough to stall the stepper, but the voltage is staying high enough to keep the processor running.

To test if this is a problem, either jumper the polyfuse (CB2) on the relay board, or replace it with a higher rated polyfuse (like RXE250-ND).

Again, I don't know if this is a likely possibility, but we are running low on things to check.

Lance.

[JSC]

Lance;

Thanks for the input, it's nice to know that others are thinking about this issue. You have an interesting idea, I do have a polyfuse in my system and I'll check it out.

Scott

[69 1/2 Six Pack Bee]

I WAS using the relay board unfortunately I took everything out so I can't test that theory.

Sorry.

[BottleFed70]

I'm still not convinced this isn't a firmware issue.

I know my MS "Thinks" it's sent X-number of steps to the stepper motor.. but has anyone actually counted the steps?

The key thing here is that all of us seem to be able to get the IAC to move if we send it large step sizes... and at least in my case, can get it to move reliably in this mannor. The exact same thing happens to me on every cold start... the IAC doesn't end up moving enough(it does move some) and my idle is too high. Turn key off and restart and the stepper moves to the perfect position, and my idle is right where I want it to be.

I can even do this multiple times during warmup. I have it set to idle at 800rpm. During warmup the engine will rev to 800rpm at 1st, then start to climb as the engine warms up. If I turn off the key and restart my idle is back to 800rpm...but again will slowly increases with engine temp. I can do this 3 or 4 times in a single warmup cycle...until eventually engine has reached regular temperature and after a restart the IAC moves to it's warm running positioin. I've tried all sorts of step size and acceleration step tweeking and I've only ever been able to make it worse instead of better. Like others I've tried multiple GM IAC's..

Again.. it seems to me that the IAC moves properly when sent a large group of steps as in a hot-start with a few second afterstart taper time. It doesn't work reliably when fed 1 or 2 steps at a time during a regular warmup cycle.

I am running a relay board and will try jumpering the polyfuse..however I have my doubts as I think that if this was the problem, I would see the exact opposite problem. (Large steps wouldn't work but small steps would)