Idle hunt, running lean, humming noise from aem intake

[mrbrossnan]

hi guys!

recently the car developed idle hunt issue and running lean as well. one thing i noticed, there is this loud humming noise coming from the engine bay. i thought it was coming from the intake manifold area but upon closer inspection i think it's coming from the aem intake pod.

any pointers as to where to look at??

car is running stg 2 with adaptronic.

cheers

[david_syd_au]

The humming noise could be from the stepper motor in the idle control valve (ICV), and is not necessarily a problem. It is not uncommon for the ICV to make such a sound when controlled by an aftermarket ECU using a different pulse frequency to the stock ECU..
Once the engine is warmed up, try disconnecting the ICV temporarily and assess if the humming noise stops.

[gslender]

The humming noise could be from the stepper motor in the idle control valve (ICV), and is not necessarily a problem. It is not uncommon for the ICV to make such a sound when controlled by an aftermarket ECU using a different pulse frequency to the stock ECU.

That'd be it... the Adaptronic should be trying to control the ICV at a fairly high frequency... depending on the model (NA6/NA8 or NB) it can be as high as 600Khz, which few ECU's can produce a PWM signal that high. So they are driving it lower and it hums. Not ideal but it will work. It would also mean the idle isn't a smooth when changing. Less frequency means a more coarse step between open and close.

G

[manga_blue]

Also check for air intake leaks.

[mrbrossnan]

Thanks for the input guys. If it's a normal behaviour then I can live with it but I just thought it could be the cause of the idle hunt. could a vacuum leak cause this as well?

Anyone running adaptronic on their SE has a humming engine as well?

[gslender]

Idle hunt could be a problem related to the PWM freq. too low and the resolution steps are too coarse and it also hums.

The ECU wants the engine to idle lower so it moves to the next step resolution in the freq but this is closing the air valve too much and the engine idles too low. Now the ECU needs to raise idle and move air valve to open more but with coarse resolution it opens too much and idle is now too high.

This see-saw will be the idle hunt. Common with incorrect freq on the idle PWM output

Some ECUs (old model megasquirts etc) had this problem - any decent ECUs like the ms3 can run PWM at high frequency and also removes the hum


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[gslender]

Is it clear to everyone reading why wrong PWM freq impacts idle valve step resolution?

Asking as I'm unsure if it helps if I explained that or not.

[Dweezle]

I am definitely all ears for a more lengthy explanation ??

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[Roadrunner]

That makes sense
Question though, you say "Common with incorrect freq on the idle PWM output"
Is it possible to change this frequency?

[Lokiel]

Is this "hum" you're describing more of a constant monotone?

I have an Adaptronic Select e440 ECU and when I set the Idle Maximum Value to anything less than 87% it would generate this continuous monotone:

There's an old thread on the Adaptronic forum where someone suggested setting the Max Idle value to 80 that Idle was easier to control so that's what I did and the tone drove me nuts. I bumped the Max Idle value to 87% and it went away - I asked Andy about this and he said he never understood why it should be anything other than 100 once the desired Idle screw position had been determined so I left it at 100%.

gslender's explanation of what's actually happening explains why the monotone is generated and why bumping the Max Idle value made it go away.

FYI from Andy: http://www.adaptronic.com.au/forum/index.php?topic=4954.0:
"Lower frequencies generally give better control but more acoustic noise."
- consider bumping your PWM frequency to make the noise "go away".

[david_syd_au]

I think the "step period" of 5mS is what sets the frequency, 200Hz in that case, and the duty cycle then varies the ratio of on/off signal to the ICV motor at that frequency.
If you were to reduce the step period to say 2mS, then the control frequency would be increased to 500Hz, and MAYBE making the hum less audible.
My NB8A has a megasquirt with the control frequency set to 480Hz, and there is still a noise, but it is not audible when the motor is running.
I know SFA about adaptronic ECUs, so you should consider consulting an adaptronic expert (aka Andy) before making such a change.

[mrbrossnan]

Lokiel,
yes sit is a constant monotone type hum, the one that hurts your hearing after a while!

Is this "hum" you're describing more of a constant monotone?

I have an Adaptronic Select e440 ECU and when I set the Idle Maximum Value to anything less than 87% it would generate this continuous monotone:

There's an old thread on the Adaptronic forum where someone suggested setting the Max Idle value to 80 that Idle was easier to control so that's what I did and the tone drove me nuts. I bumped the Max Idle value to 87% and it went away - I asked Andy about this and he said he never understood why it should be anything other than 100 once the desired Idle screw position had been determined so I left it at 100%.

gslender's explanation of what's actually happening explains why the monotone is generated and why bumping the Max Idle value made it go away.

FYI from Andy: http://www.adaptronic.com.au/forum/index.php?topic=4954.0:
"Lower frequencies generally give better control but more acoustic noise."
- consider bumping your PWM frequency to make the noise "go away".

[gslender]

I think the "step period" of 5mS is what sets the frequency, 200Hz in that case, and the duty cycle then varies the ratio of on/off signal to the ICV motor at that frequency.
If you were to reduce the step period to say 2mS, then the control frequency would be increased to 500Hz, and MAYBE making the hum less audible.
My NB8A has a megasquirt with the control frequency set to 480Hz, and there is still a noise, but it is not audible when the motor is running.
I know SFA about adaptronic ECUs, so you should consider consulting an adaptronic expert (aka Andy) before making such a change.

Unsure given I can't be certain where in the Adaptronic ECU it defines the PWM frequency. It does seem likely that Step period is the right setting and I agree with David's explanation that setting it to 2ms would be the correct frequency for a MX5 idle valve. I'd suggest changing it to 2ms and see if it improves the idle and noise.

G

[gslender]

I am definitely all ears for a more lengthy explanation ??

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PWM - Pulse Width Modulation is a way for a digital device (ECU) to variably control voltage. It quickly turns 12V on and off to simulate a lower voltage. If you see 12V half of the time then technically it would look like 6V and then the idle valve would be half open. This relies on a combination of the frequency of the PWM control voltage and the mechanical spring and the motor in the valve.

Obviously in reality the valve is closing and then opening (at the frequency) and if you have this too slow, or too fast it will not have the effect needed based on those mechanical characteristic design to work at the correct voltage - it needs to be at the correct harmonic values to operate correctly and have the right effect of moving the valve in the way it was mechanically designed to work.

As this is essentially a harmonic behavior you can get the valve to go from closed to open through a range of frequencies, but at lower frequencies the number of harmonic steps are much less. Let's assume there is a natural step every 10Hz. With a range of 100Hz you only have 10 steps between closed and open. With the frequency at 1000Hz you now have 100 steps between closed and open. Also, at lower frequencies the valve is more slowly moving and so will more likely hum as it wasn't designed to move that slow. The same thing also happens when you drive the valve too high, it oscillates above its mechanically design frequency and can also buzz or hum etc.

Hope that explains it sufficiently.

G

[Dweezle]

THANK YOU! !!

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