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I haven't adapted this car for a while, but interestingly another car I tried to adapt had exactly the same IAC trim showing on Scantool. Maybe adaptation isn't as significant as we think?
Re duty cycle, my longer video showed that it was settling at ~ 63% when happy and warmed up, stayed the same when the throttle opened and went to ~ 78% when bringing the idle up from a throttle closed position.
Logically, the duty cycle is important when the idle circuit is on, as the ISV bypass is the only source of air to the engine and it appears that more duty cycle = more activation = more air = more revs.
When my new spare arrives from China I'm going to put it apart, cut a view hole, put plastic over the hole and film what's going on. Why? Well it's about understanding what's going on with duty cycle so that in future I can insert my test cable, measure the duty cycle and help diagnose hunting idles etc.
I have read that fuel adaptation was needed more for C4s than C2s and earlier car's more than later. Another reason I thought the wires were reversed as this could have been an undetected build fault that was later corrected.
The popping up to 78% is consistent with ISV providing a 'soft landing' on throttle closure at higher rpm then easing down to 63%.
If you could lay your hands on a pulse generator with enough amperage you could bench test the valve without cutting it open. I suppose you wouldn't need a pulse generator, just power supply setting it to average voltage as that's what ISV responds to.
If your feeling inquisitive, you could try reversing the leads and see how car runs (or doesn't). If it manages to idle, you might replicate dreaded throttle bounce. The throttle bounce comes from the ECU sensing idle undershoot as valve is closed at this point, overcorrecting, then settling down. Or you could see on bench test if equivalent reversed signal at 78% (or whatever unadapted value is) closes valve as I suggest.
It's amazing how much better my car ran after adaptation. Maybe initial settings in ECU were just wrong and adaptation corrects that. Not sure that's the case as SW chip had no effect on poor unadapted performance.
Reading the 993 thread again, the duty cycle I’m seeing is equivalent to the opening duty cycle on the dual solenoid version. I’ve heard that a 9v battery will move the ISV, but I don’t have a voltage or pulse width generator. My plan now is to fit longer wires to the test lead (I have 19 spares to play with!) then I can put the multimeter next to the tachometer, put the go pro on and do some driving. I will also do an adaptation and see if the ECU powers the ISV. It’s a learning exercise. The goal is to diagnose hunting idles using the base data on a working ISV.
The ISV works in one direction only no matter which polarity you put on the pins. The opening is relatively small when fully open so it must be a very fine metering control.
The only confusion in my mind is the logic of the duty cycle. If the valve is open when no power is applied then surely applying power is reducing the air flow. I need to think this through.
This morning I had a mini brain wave and reversed the leads to the multimeter. Sure enough, it read the opposite duty factor i.e. 63% became 37%. I have a spare ISV arriving soon and will see how I can modify it to watch how it works in action.
Isn't full voltage swing 15v? Then 9v would be 60%
Originally Posted by John McM
The ISV works in one direction only no matter which polarity you put on the pins.
Due to stop, the solenoid can only go one way, I'm surprised reversing leads doesn't pin it against stop in one orientation. Must have equivalent to full wave bridge on input.
Originally Posted by John McM
The only confusion in my mind is the logic of the duty cycle. If the valve is open when no power is applied then surely applying power is reducing the air flow. I need to think this through.
In the video are you looking at input or output?? On my old valve, small gap is apparent on output side and I can open it further manually. If you attempt to open valve manually using a prying tool (you will scratch the surface, so do this on throw away valve) you'll find valve reopens at some point, IIRC. This why I guessed the wires might be reversed. Whether or not a high duty cycle will drive valve that far remains to be seen. You can try 12v on valve I guess. This would be equivalent to 80% duty cycle.
Check to see if pins are isolated from case. If one pin is grounded to case, reversal of leads would be a no-no when case was grounded.
I have to take another look at video...
Ummm. Looking down output port with ISV pins to the right as in video, my old solenoid shows a gap towards 'top' of port so that rotating valve increases gap size. Your video shows gap towards bottom so rotating valve closes gap, if I'm seeing it correctly.
Last edited by dlpalumbo; 06-11-2018 at 08:35 PM.
Reason: Looked at video again.
I sourced another Bosch ISV and it had the same characteristics. The video is showing the engine side of the ISV outlet. 9v fully closes the valve.
It appears to me that no voltage to the ISV should allow the maximum bypass and full voltage closes it. I expect my AliExpress ISV to arrive in the next couple of days. I think the next thing is to pull apart an ISV as per above.
Ummm. Looking down output port with ISV pins to the right as in video, my old solenoid shows a gap towards 'top' of port so that rotating valve increases gap size. Your video shows gap towards bottom so rotating valve closes gap, if I'm seeing it correctly.
What is the part number on your ISV? I can’t see how mine closes with voltage and works on my car, yet yours is working in the opposite sense.
What is the part number on your ISV? I can’t see how mine closes with voltage and works on my car, yet yours is working in the opposite sense.
Bosch 280 140 531 is P/N on box new part came in. Old part is 280 140 5?? as label is torn away. Dont have a 9v battery handy, but there's only one way for this to turn. Label says its a 12v device.
I'm not clear on your previous post as to what happens when full voltage is applied. it could be valve reopens as I have suggested.
This is viewing the outlet pipe and applying 12v from a car battery. It would likely open even more when 15 volts is applied. Note that the action is the same no matter what polarity is used.
In an earlier post I mentioned that AliExpress have new ISVs for USD 47. They are so similar to the Bosch version that they are either a very good copy or have been produced in the same factory.
Here are pics of a Bosch ISV and a shiny new AliExpress ISV.
I tried to fully actuate the ISV. What I found is that it hit a stop. See photo:
Input side of ISV showing 'stop'.
Sorry for poor quality and huge size. I don't have ability to resize photo. Circled is stop against which valve bottoms when forcefully opened to full extent which corresponds to valve being fully opened on output side. So my guess that valve can close upon itself is wrong.
It could be then, that for an un-adapted car, the fuel is actually cut off by ECU when the idle switch is engaged and rpm is above idle. I had thought air was cut off by ISV. 'Fuel Adaptation' then sets fuel flow under this condition so rpm can fall gracefully. This would be conservative approach to avoiding too rich a mixture under these conditions. It could also be, that in later cars Porsche figured a less conservative approach which reduced need for adaptation. Having to adapt car is a giant pain, especially with my car's tendency to drain battery if left too long.
John: Any comment on what was going on in earlier video when valve seemed to be closing with applied voltage?
John: Any comment on what was going on in earlier video when valve seemed to be closing with applied voltage?
The no power state has a small gap, probably as a default to allow some chance of idle, if the ISV fails.
When I applied 9V, that gap closed, leading me to believe that was the normal function. I was WRONG, as when I applied 12V the valve continued in the same direction revealing a large opening. So higher duty cycle is more power to the ISV, opening the valve more, giving more air and higher idle. BTW: neither of the plugs are to earth and polarity of the signal makes no difference.
Next step is to locate one that is causing issues and open it up for a full clean. It appears this is done by 'dremelling' off the metal tabs holding the plastic in.
05-29-2018, 09:56 AM
