Hello.
Can anybody give some idea about idle valve PWMing: generally it works, but IAC give out rattling sound. It is irritating at engine off/ignition on. With scope it looks like PWM is very irregular but give average duty cycle as desired. Changing of frequency does not help much. Only change rattling a little. What here can help? Big capacitor or something? I have this problem on two cars with simple 2-pin IACs of different constructions: Audi 7A engine and Mazda 323F '89 with 1.5L engine (turbo now ;))
Gints
Have you tried an external flyback diode?
External? I drive it from INJFET and my flyback 30V diode is inside VEMS - it's for Mazda. In Audi case I use Power Flyback board - so relative low voltage flyback. May be I try to high frequencies: put 1...10 in Megatune? And separate firmware branches is used too: for Audi 1.1.15 or 18, for mazda 1.0.73. Both have rattling.
Does someone suffer from this or this is problem for me only?
Gints
I've found that the IACV clatters on a few of the installs that I've done, its one of those 'features' that goes away if you turn the ignition off. One of the spare 1N4004 diodes would be worth trying.
What firmware are you using ?
On v1.0.53 for sure most of the PWM frequency options in MegaTune run the stepper at a low frequency (10hz ish). The duty cycle control isn't very constant and this causes the stepper to jump about. However if you pick a PWM value which is a multiple of 64 (0, 64, 128, 192) then the output runs at 1.2KHz and the stepper movement is smooth. Give it a try.
Hilly
Did you mean this?
(http://quasar.dynaweb.hu/~lezsi/vems/iac_speed/iac_speed-pwm.gif)
Gints
I got caught out by the idle PWM as well, my Bosch valve was rattling about like a mad thing.
I expected the iac speed to look something like the chart you posted, but I measured it with an oscilloscope and it was all over the place.
This the the value in MegaTune
(http://i67.photobucket.com/albums/h286/s3esprit/idlepwm.jpg)
I started at 1 and kept incrementing the value whilst measuring the frequency and found no patteren until I hit 64 and it then jumped up to 1.2KHz and the valve worked like a charm.
Hilly
If you started at zero you'd find that the result would have been the same - I've showed the development team these findings and was shown: IACFREQ_PWM ((4 + (config.iac_speed & 0x3F)) << 7) so 64 is same as 0
Yes. I just try it with scope on stimulator. Looks like ~680Hz (?). And yes much more stable like any other setting. Still fluctuate, but discountinuties is much shorter - ~1ms. with others 5ms and longer pauses is a norm. It causes valve clicking.
Does so high frequency can't give some heat problems?
So next week will try 0 on Mazda.
There should be no increased heat problems as the power to the stepper is still the same, PWM remember.
The flyback diode will have to work harder due to the increased number of edges it is suppressing, but no worries there either.
Hilly
I've just been given the following instructions: To stop the IACV clicking:
Set iac_cold_start_pos & iac_warm_start_pos to 0.
That does stop it too, but iÃ,´m using speed 0. IAC valve works much smoother with that.
Is there a reason to why not use it in 0 speed??
In some cases 0 speed will be too fast for certain solenoids to react, if you're getting good results then stick with 0.
We have a same rattling problem, but with BY399 3A fast diode from shop.
Is it good for this? Or need change to 1N4004?
Anyway the iac actuator speed not mean frequency in Hz but the table values above. So maybe 1-15 valid?
Can I try the 64 value?
Quote from: [email protected] on October 25, 2007, 09:49:11 PM
I've found that the IACV clatters on a few of the installs that I've done, its one of those 'features' that goes away if you turn the ignition off. One of the spare 1N4004 diodes would be worth trying.
Usualy only acceptable value is 0. signal isn't true pwming, but some kind of pseudo pwm - irregular and with interrupts.
Any diode should do the job.
May be some capacitor can help to mask rattling?
Gints
Quote from: GintsK on June 04, 2009, 01:46:45 AM
Usualy only acceptable value is 0. signal isn't true pwming, but some kind of pseudo pwm - irregular and with interrupts.
Any diode should do the job.
May be some capacitor can help to mask rattling?
Settings for IAC speed are between 0 and 15.
0 = ~ 250 Hz
15 = ~50 Hz
A high frequency makes the solenoid lazy, reacts slowly to small changes. Too small frequency makes it oscillate and might hit the end positions (rattle noise).
I use 6 which is about 100 Hz and works very well with dual coil ICV on my BMW E30 (1980s 3-series). It is a bit quieter than the stock frequency which is lower, easily heard with ignition on, engine off. It is a 3 pin deal, with two solenoids working against each other and uses two outputs on the ECU (one inverted) and is probably designed this way to prevent dependancy on battery voltage.
Without diodes to control solenoid flyback voltage you won't get anywhere in adjusting the idle. I use the diodes that come with the rescue kits, 1N4007 which can handle 1A. Not sure if it's the perfect one for the job but a Schottky diode like SR806 that can handle 8A and is faster than the 1N4007.
- Anode to switched point of the solenoid (channel output, EC18-pin..)
- Cathode (marked with a line) to the other pad of the solenoid: the same where you connect the positive +12V (switched and fused) power
Interesting.
On my table I see: it is not PWMing. And 250Hz is not 250Hz.
I will try to explain what I see on the scope.
250Hz is 250Hz only at 50% duty cycle.
Any other average duty cycle is achieved with combinations of positive and negative pulses of exactly same duration as 50% pulse.
Lets say 80% is one positive and four negative pulses (in fact one 4 times longer negative). But frequency is 2.5 times lower than at 50/50, because polarity changes only every 5th pulse.
80% is simple. But something like 82% means time to time more than 4 pulses at once will be together (every 5th period IMO). And this is a cause of rattling. such pulse can be long enough for full IACV opening and clack.
10% and 90% gives 5times lower frequency.
5% and 95% gives even 10 times lower frequency. (only 25Hz at 0-setting)
Closer to 0% or 100% duty cycle means more rattling and lower frequency.
Can some hardware specialist clarify why this pseudo-PWMing strategy is used?
Gints
Basically it's an incorrect implementation of PWM in the VEMS firmware. "IAC actuator speed/pwm freq" (config iac_speed) is correct only when the solenoid is at 50%/50% (iac_max_steps = 128).
As you've observed, the frequency changes as the solenoid moves away from the 50/50 duty cycle since the pulse length is fixed. It's clearly not an appropriate approach for an electromechanical device like the ICV which operates reliably only within a specific PWM frequency range (probably 80-300 Hz).
Another problem I've observed is the intermittent spurious pulse lengths on the first channel that causes rattling even at iac_speed=6 (100 Hz) and 50/50 duty cycle.
(http://e23.bimmerclub.ph/images/vems/20090704-iac-scope.png)
Related thread here: http://195.159.109.134/vemsuk/forum/index.php/topic,917
No hardware can fix the issue. The firmware IAC routines have to be re-implemented.