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zoti Samba Member
Joined: December 26, 2007 Posts: 2039 Location: Plano, TX USA
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Posted: Sat Aug 28, 2021 7:39 pm Post subject: More idle control issues. |
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As part of the development of the idle control unit I am testing the ones I have.
1988 2.1L Digifant. I have 2 idle control units. One is a rebuilt by module master. The other is just a B model.
Testing per the Digifant trouble shooting manual for 430MA +-
20MA at idle and I only get about 26MA reading. That's on both the rebuilt unit and other unit.
The idle control valve does open a bit. If I disconnect it, the idle drops a little. I can also connect a second valve I have and see it open
Running both units off a 12v power supply on the bench gives me the same results. I power them by connecting 12v to terminals 15 and 31. See diagram below.
The ICU also gets power on terminal 50 and I am trying to figure out why exactly. So far we think it's a signal to the ICU that the starter is engaged.
I should note that other than the slight rise in RPM that is always there, the ICU does not seem to raise idle when the power steering is engaged or the power steering terminals are jumped together.
Looking for insights from more experienced people.
Tomorrow I am planing to test each and every wire. I find it hard to believe that both and especially the rebuilt idle control units I have are defective. |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4715 Location: Bemidji, MN
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Posted: Sat Aug 28, 2021 7:46 pm Post subject: Re: More idle control issues. |
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the throttle body plate rest point is a crucial measurement, set via vacuum specs on the TB canister valve port. if that is too open, the ICU will not have the range of adjustment at its disposal. _________________ -dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10347 Location: Sunshine Coast B.C.
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Posted: Sat Aug 28, 2021 7:52 pm Post subject: Re: More idle control issues. |
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AFAIK, the idle control system (i.e. valve) compensates for added loads. IOW, instead of raising the idle when PS and/or AC loads are introduced it tries to maintain the idle speed by allowing more air into the intake.
50 positive would be present when starter is engaged. I don't think you should see 12 volts positive at that 50 pin/wire at any other time.
Neil. _________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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zoti Samba Member
Joined: December 26, 2007 Posts: 2039 Location: Plano, TX USA
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Posted: Sat Aug 28, 2021 7:57 pm Post subject: Re: More idle control issues. |
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Vanagon Nut wrote: |
AFAIK, the idle control system (i.e. valve) compensates for added loads. IOW, instead of raising the idle when PS and/or AC loads are introduced it tries to maintain the idle speed by allowing more air into the intake.
50 positive would be present when starter is engaged. I don't think you should see 12 volts positive at that 50 pin/wire at any other time.
Neil. |
I agree about terminal 50.
I used an oscilloscope to try and read the pulse of the ICU. (It works great when reading the hall sensor). All I get is a dirty signs. Nothing stable. |
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zoti Samba Member
Joined: December 26, 2007 Posts: 2039 Location: Plano, TX USA
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Posted: Sat Aug 28, 2021 8:00 pm Post subject: Re: More idle control issues. |
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DanHoug wrote: |
the throttle body plate rest point is a crucial measurement, set via vacuum specs on the TB canister valve port. if that is too open, the ICU will not have the range of adjustment at its disposal. |
That would be the throttle position sensor input which is adjusted correctly. |
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zoti Samba Member
Joined: December 26, 2007 Posts: 2039 Location: Plano, TX USA
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Posted: Sun Aug 29, 2021 9:52 am Post subject: Re: More idle control issues. |
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I have basically tested everything I can on this and the only conclusion I have is the both idle control units are defective. Even the one that was refurbished.
I have power to the ICU. I have hall sensor signal. I have temp signal and the resistance is exactly where it should be (I get 230Ohm at full warm engine).
Yet I can't get 430ma at the idle control unit or pull a signal off it with the oscilloscope but the valve is slightly opening and raising the idle.
It will not raise idle when I bridge the power steering switch. Not sure about AC because my AC was removed by the previous owner so I just have the wire that went to the compressor. I don't know if the ICU receives a signal from that wire or ground when you turn the AC on. |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10347 Location: Sunshine Coast B.C.
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Posted: Sun Aug 29, 2021 10:56 am Post subject: Re: More idle control issues. |
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ziti wrote: |
Yet I can't get 430ma at the idle control unit or pull a signal off it with the oscilloscope but the valve is slightly opening and raising the idle.
It will not raise idle when I bridge the power steering switch. Not sure about AC because my AC was removed by the previous owner so I just have the wire that went to the compressor. I don't know if the ICU receives a signal from that wire or ground when you turn the AC on. |
Double check this but '86-'89 AC wiring diagrams show a positive wire to ICU; as AC compressor clutch relay closes, positive gets connected to ICU. (to pin 2K, I think).
I guess if van is stationary, one would expect to hear/see the idle increase if the PS switch wires were connected eh?
Somewhere in this forum there's a pic I posted of a Mercedes idle valve showing its' valve positions at various duty cycles. IIRC it's similar to the Vanagon idle valve.
Neil. _________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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RawUmber Samba Member
Joined: June 23, 2019 Posts: 223
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Posted: Sun Aug 29, 2021 11:30 am Post subject: Re: More idle control issues. |
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26mA is obviously out of spec, and might not be able to operate the ISV at that point. Is the amp meter hooked up correctly? It should be in series with the load (ie, ISV). Ex: between the ISCU ST2 and the ISV pin3.
ISCU terminal 50 is the Starter signal (~12V active). ISCU reduces the ISV's air flow when starter is cranking.
Idle RPM should step up slightly when Power Steering Pressure Switch (LH) is active. Same with active AC (also ~12V active).
Try your oscope on ISCU terminal ST1. If you don't see a sq wave that's ~10V peak to peak, it might be related to that limited current ('26mA'). |
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zoti Samba Member
Joined: December 26, 2007 Posts: 2039 Location: Plano, TX USA
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Posted: Sun Aug 29, 2021 1:23 pm Post subject: Re: More idle control issues. |
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RawUmber wrote: |
26mA is obviously out of spec, and might not be able to operate the ISV at that point. Is the amp meter hooked up correctly? It should be in series with the load (ie, ISV). Ex: between the ISCU ST2 and the ISV pin3.
ISCU terminal 50 is the Starter signal (~12V active). ISCU reduces the ISV's air flow when starter is cranking.
Idle RPM should step up slightly when Power Steering Pressure Switch (LH) is active. Same with active AC (also ~12V active).
Try your oscope on ISCU terminal ST1. If you don't see a sq wave that's ~10V peak to peak, it might be related to that limited current ('26mA'). |
I made a VW 1315a/2 copy. I tested one wire based on what I saw online. I will try the other wire.
26ma is definitely low but it does open the valve. I was expecting to see the valve vibrate but it just holds it open in a position which seem to raise the idle a bit compared to when the plug to the valve is disconnected.
This is the tool I made. I disconnect at the blue circle and connect the meter there in series.
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