MSefi.com read only forum (Jan.15,2018)

I have a Mercedes 500 SEC which I am working on converting to MS.
One of the questions that came up during the IAC planning was what in the world the IAC control on the current system (Bosch CIS) was, and could I get MS to control it.

Here is an excerpt from the Mitchel On Demand manual entry on the emissions system for this car. I've tried finding info in a few other locations, but this is most information I've been able to find on the IAC motor/solenoid/thing...

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Idle Speed Adjuster
The idle speed adjuster is an electrically controlled solenoid that opens and closes an orifice. With the ignition off, the orfice is completely open. With the ignition on and the engine not running, the orifice is open and the adjuster is operated by 0-1.5 volts from the control unit.

When the engine is running, the orfice is decreased in size as the adjuster receives 4-5 volts. At 5 volts, the orfice is closed. When the engine speed is over 900 RPM, the orfice is kept slightly open by 4.5 volts so that the engine will not stall if the throttle is closed suddenly.


Electronic Control Unit
The control unit receives voltage from the voltage supply relay. It also has inputs from ignition system (to determine idle speed), an oil temperature sensor, air injection ssytem and fuel injection feedback control unit. It provides an output signal to the idle speed adjuster which varies from 1 to 5 volts, at a frequency of 200 cycles per second.
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Does this look like standard behavior for a PWM IAC? Is this within the realm of what the MS PWM circuit is designed to control?

Sorry for the lack of understanding here, I'm having a fun time trying translate from non automotive applications of electronic usage into the physical controls that they are being used for in automotive applications.

Thanks for any information you care to share.

If it'd help any, here is a picture of what the device looks like.

I'm still trying to figure out what the control scheme is for this valve, hopefully it'll be possible to control via megasquirt, rather than having to replace it with something else.

That looks like a standard PWM IAC valve. MS should be able to control it once you have modified the transistor to a higher power rating type. If it really operates from a 5V source, you'll need to get the 5v from somewhere else. MS will supply a switched ground. I have a similar device from a mid 80's Saab. Some operate normally closed, others, normally open. If it is usally warm, normally closed (ie no power = closed) might work better.

http://www.megamanual.com/ms2/IAC.htm#fidle

- Charles.

Well, I'm fairly sure this is a normally open valve, as when I unplug it, it revs up to around 1800rpm.

As far as the 5v control goes, I've just recently found testing instructions calling for up to 12v in momentary use to test it, so I suspect anything the MS can dish out should be workable, at least when controlled, rather than just applying 12v directly.

Thank you for the reply and information, though!

How is this conversion going?

Unfortunately, the project has been on hold for the most part.

The daily driver car became unreliable, so the EFI conversion subject has become the daily driver.

Parts collection is complete other than some fuel hose and preparation for the conversion is still in progress, but running slowly at the moment.
Hopefully once new employment is worked out, I'll be able to dedicate more time to the conversion again.

Keep in-mind Bosch made several styles of PWM valves (I don't know why ). One I used looked similar to the picture and had an open-closed-open operation, so the flow was something like:

0 PW = slightly open
25 PW = closed
50 PW = slightly open
75 PW = fully open

This way, a failure would allow starting and running, although idle would be high even warm. I would suggest bench-testing any valve to check operation before installing, as it can save a lot of time and frustration.

David

PSIG wrote: I would suggest bench-testing any valve to check operation before installing, as it can save a lot of time and frustration.

Well, the valve is working on the stock intake system currently, so at least I know that it is working.
I'll have to see what I can do with the MS on the stim before installation, but I can't really see any way to break out the fast idle to play with it while on the stim. (and I need to do the PWM fidle mod still...)

Thanks for the pointer about possible behavior, I'll somehow see if I can test just how it behaves!