Stepper motor issues with homing steps and idle speed

[B1ack_Mi16]

Hi there.

Finally got the new coils and fired the engine again. I've been having this issue for a while now, that I can start the engine and it will rev high, temps increases and stepper motor closes however idle might still be around 1500rpm (should be 850-950 area) if stepper is completely closed.

I can stop the engine and re-start it and it might settle to the target speed straight away.

I'm not sure what to do, but it seem like there is a problem with the stepper not moving fully home before it starts to open?
Can it be related to that I've set a lot of homing steps so that it doesn't have time to move fully home until it I try to start it?

I've tried it with another valve too, without any change in behaviour.

2017-07-28_10.46.04_ReBinned.msq

[B1ack_Mi16]

Btw. the problems was there before too and I have increased the normal time step from 2ms to 3ms, and the first one from 3ms to 4ms as it seem to move very good in test mode using 2ms.

Largest number of steps is 90 for cranking and I'm using 256 homing steps now in the last test, just to try to be absolutely sure it will go fully home before it starts to open.

[Matt Cramer]

Try increasing the homing steps.

[billr]

Also, using "always on" or "holding current" is more reliable than "moving only".

[B1ack_Mi16]

Try increasing the homing steps.

I really tried from 100 and up til 256 now.. so you really think I shall make it do like 1000 homing steps?
Normally after it has been started it should not be at more than 45 steps at coldest warmup setting, hence I thought 90 should in theory be more than enough, unless the engine stalls exactly during cranking?

[B1ack_Mi16]

Also, using "always on" or "holding current" is more reliable than "moving only".

After my stepper chip broke I was told it was not recommended due to the chips are prone to failing with those two options activated, anyway it doesn't seem to move at all even though it is set to "moving only", so I don't think that would really change anything.

If that was the problem shouldn't the stepper possibly move and hence also the idle speed when it is finally up to temperature and still beeing too open if that was the case?

[jsmcortina]

After my stepper chip broke I was told it was not recommended due to the chips are prone to failing with those two options activated

I've not heard that.

James

[billr]

What is the resistance of your stepper coils? Those drivers are pretty durable if used within their design limits.

[B1ack_Mi16]

After my stepper chip broke I was told it was not recommended due to the chips are prone to failing with those two options activated

I've not heard that.

James

This is what I got on e-mail from Diyautotune. Hence I'm not too eager running other settings than moving only, at least as long the stepper don't seem to move in between steps anyway. My problem is related to what happens usually at first startup I believe.

Hello,

There are some resistor and caps that are changed.

It is important to make sure the settings for the IAC are also set to energize while moving only.

Thanks,

Phil Koch

DIYAutoTune.com Technical Support

[billr]

I'll ask again... what is the coil resistance of the stepper?

This is an MS3 Pro? I probably better bow-out. I was thinking of the standard MS3 when saying that the stepper driver is pretty robust, but don't really know about what is on the Pro. I would hope the Pro is at least as good, but don't know.

[jsmcortina]

I'll ask again... what is the coil resistance of the stepper?

This is an MS3 Pro? I probably better bow-out. I was thinking of the standard MS3 when saying that the stepper driver is pretty robust, but don't really know about what is on the Pro.

Same part, same design.

James

[billr]

So, we are down to the stepper coil resistance now. We need to know that value to avoid just guessing further.

[B1ack_Mi16]

Thanks. Measured it now, more or less 53 Ohms on both coils.

It is this type / design:

[billr]

With 53 ohm windings there should be no problem using "always on". I'll have to ask Matt C. to comment on the advice you got from DIYautotune; it makes no sense to me.

[kjones6039]

FWIW................ I use the same iac on my big Holley TB. I have never had a problem with 'Always On'. In fact, it seems to be more reliable in that mode.

I would be glad to check the resistance of one of my spares in the morning, if that would help.

Ken

[B1ack_Mi16]

If you could be bothered that would be interesting indeed.

I checked on a spare I have as the one on the car is not easily accessible, but I've tried them both during testing and they seem to behave the same at least.

I got the advice after my stepper chip broke. I changed it myself (however DIYAutotune was willing to fix it all for me under warranty, but I couldn't be bothered sending it so far due to the time delay).
It was during this discussion they adviced there were some additional components that ideally should be changed to make it more robust in addition to just use "moving only".

[B1ack_Mi16]

FWIW................ I use the same iac on my big Holley TB. I have never had a problem with 'Always On'. In fact, it seems to be more reliable in that mode.

What do you put in the word reliable in this context, does it act like mine and you get the wrong idle-speed if not using "Always On"?

[Matt Cramer]

With 53 ohm windings there should be no problem using "always on". I'll have to ask Matt C. to comment on the advice you got from DIYautotune; it makes no sense to me.

It was very specifically a combination of always on, low coil resistance (53 ohms is not low coil resistance - this would be more like 20 ohms) and some of the MS3Pro units before they received a change to the bill of materials. I wouldn't worry about breaking this one. A lot of the GM IAC valves need 320 to 500 steps.

[kjones6039]

If you could be bothered that would be interesting indeed.

Quick trip to the garage this morning........... ~50 ohms............

Ken

[billr]

I gotta ask... did the OP replace those "other components" along with the failed stepper IC? Is the IAC valve that was in place when the driver failed 53 ohms, or is it long-gone, unavailable for measuring now?