M4 Pro idle control oddity

[lloydie]

Hello,
Im using Aux 1 to control the idle on my Mazda BP engine, using an M4 Pro. The idle control on my is great, car idles fine from cold or hot BUT the IAC valve duty never drops below 75% regardless of the revs. I thought it decayed to zero when the TPS was over 2%, but ive got a good TPS signal and logs showing TPS over 50%, revs over 3500 and the IAC duty stuck at 75% !! What else is the duty goverend by and am i missing something obvious ?
Ive attached a screen from Interpreter.
Ive also got a probelm with sequential injection (so its running batch), but thats probably best saved for another thread as i dont think it has a bearing here.



Thanks

[tkkhoo]

There is a setting for minimum duty cycle in the Idle Speed Control parameters.

TK

[lloydie]

There is but its set to 5%, and it should still be goverend by the TPS being waaaay above 2%......

[MarkMc]

Email the configuration to support@motec.com.au attention to me an I'll have a look.

[lloydie]

Have you received it Mark ? (sent last week)

Thanks

[MarkMc]

Sorry lloydie,
I sent an email back.

Basically there is no problem, the resting duty cycle is based on the PID setup and the Integration limit. You could bring this resting duty cycle down but that would involve re tuning the idle control. Your frequencey is a little high at 1000, haven't seen an idle valve with that much, too high a value can reduce the workable range of duty cycles the valve can use. What valve is it.....it's a 4g63 engine isn't it?

if you ever grab a valve off another car you should get it off an engine that is about the same size. Then it is alway good to be able to find out what is the frquency the factory ECU runs the valve at.

Characterizing valve can be a bit involved. If you run your valve just as a straight duty cycle output (output function 3) you can run through the whole range of duty cycles and see the effect on idle RPM (need to keep an eye on mixtures and ignition advance.

You are looking for a frequencey that gives a nice, wide linear range which means for 10 more duty you get about the same change in RPM, add anoth 10 and get roughly the same increase again. Where the valve is non-linear is usually at low duty cycles and at high duty cycles. What you might see is from 0-20% duty cycle you get no increase in RPM, from 20-80 you get a nice linear increase. From 80-100 you again get no change. In this case the minimum duty you want to use is 20 and the max is 80. If you find from 0-65, say, gives nothing and the linear range is very narrow, say 65-80 and the change in RPM is small you probably have the frequency too high.

But again, if it is working fine now it might be easier to leave it alone but if you have some spare time and are interested do my duty test above and let me know.

[lloydie]

Mark, the engine is a Mazda BP4W as fitted to the late MX5 (2000-2005). Ive scoped the stock idle control signal and it runs a frequency of approx 500hz. When trying this on the Mtoec i got a terrible hum from the idle control unit, so experimented with various frequencies using the output test function until the hum went away. Not very technical i know....When the engine then ran at the 1000hz setting, i kept it in there and tuned around it. I'll set it back to 500 and see how different the idle control reacts.
Failing that, like you say, i'll complete a custom table. It should be very simple as i dont want any duty above 10% throttle and say 1500rpm, so its only about 6 tbale entries to fill in.

Thanks

[MarkMc]

Hi Lloydie,
Think of an engine with no idle vavle, it will need a certain amount of air bypass so it can idle at all, this is your base idle air bypass. This bypass air is there regaurdless of if the throttle is open or not, opening the throttle is simply adding more air and therefore the RPM goes up.

Put an idle valve on it and things are exactly the same, the engine needs the same idle bypass to idle at the same RPM as with no valve. If this base idle air bypass is at 75% of duty then that just what the engine needs to idle and again opening the throttle just adds air to make the RPM go up, it does not mean you must close the idle valve at higher throttle openings.

The test I described is only to show the effects of different duty cycles on the RPM and this will be affected by frequencey. The duty cycle thing is a test to find the max and min duty values for the idle control function and can't be used to replace closed loop idle control.

The hum could depend on the frequency AND the minimum duty cycle you are using.