General 1990 ISC motor – reverse polarity for new part?

Posted by We're on Boost, Oct 1, 2017

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  1. We're on Boost

    We're on Boost Proven Member

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    When plugging in a new Airtex or Standard Motor Products ISC to my 1990 harness, it runs backwards.
    The pintle extends when you turn the key on, and retracts when you turn the key off. That’s backwards.
    My original 1990 ISC does it right.
    The pintle retracts when you turn the key on, and extends when you turn the key off.

    I’ve looked through lots of ISC posts and haven’t found anybody else reporting this.
    Seems I will have to reverse the polarity of one of the field coils to reverse the direction of the new motor, unless there is some other explanation.
    But everybody says the wiring is the same for 90 vs 91 and later ISC’s.

    Does anybody have an idea what’s going on? It just seems wrong.

    The original 1990 ISC tests at 30 ohms on all 4 coil pins. I pulled it out of the car after a few episodes of galloping idle, high idle, and finally at the end it was making a loud clicking noise like a fuel pump whenever the ignition key is on. But it quit making that noise so that now I can do testing on it without any drama.

    I’ve looked at the ISC drivers on the ECU board and they don’t show any physical damage, in fact they look brand new like fresh from the factory. LOL. 1990.
    The ECU board looks clean and nice from what I can see on top, capacitors were replaced by ECMtuning when they did the whole EPROM conversion and so-forth in 2015.

    ECU is a 1990, with ECMlink V3.
    Logs show ISC steps at 120 when I first turn the key on (engine cold), which then goes to 90 when I turn the key off. That I believe is normal. That 30 steps makes the pintle move about .040 to .060 inches, as near as I can measure it (about 1 to 1.5mm).
    All 3 of the ISC’s are at about the same initial position when disconnected – with the pintle tip at about 1 and 11/32 inches out from the flange face.
    All 3 of the ISC’s move about the same amount – just the direction is opposite!

    The 2 new ISC’s I bought from Rock Auto for about $80 each and they look beautiful.
    They are listed here:
    http://www.rockauto.com/en/catalog/...,fuel+&+air,idle+air+control+(iac)+valve,6072
     

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    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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  2. 19Eclipse90

    19Eclipse90 DSM Wiseman

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  3. We're on Boost

    We're on Boost Proven Member

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    Wow, I think that thread is saying the same thing I'm saying, except I haven't tried it yet (swapping the wires). Thanks for posting!

    In post #5 he says "The lower row left and right side need to be switched" (at the plug) which, no diagram, but I think he is saying the same thing I want to try.

    The connector pins which are numbered 1 through 6, he is probably saying to switch #4 and #6 with each other. That reverses the polarity of one of the field coils.

    Stepper motors are either bipolar (4 wire) or unipolar (6 wires or 5 wires). The bipolar ones for sure will go the reverse direction if you swap the wires to just one of the coils (not both).
    I think it works the same for unipolar steppers, and unipolar is what we have on these cars.
    So, #1 could be switched with #3
    or #4 could be switched with #6.
    Either should work.

    I'll change that last bit of harness that I have to extend anyway, because the 1990 harness isn't long enough.
     
    Last edited: Oct 1, 2017
    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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  4. 19Eclipse90

    19Eclipse90 DSM Wiseman

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    :thumb:

    The way the factory would have it would be swapping pin 4 (white, on a '90 would run to ECU pin 67) and pin 6 (black, on a '90 would run to ECU pin 68).
     
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  5. We're on Boost

    We're on Boost Proven Member

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    Ok I'll do it that way. Thanks!

    Here's a nice pic of the original 1990 ISC that was in my car. This car is an early 90, built in September of 1989. Pic is 4240 x 2832 pixels so it will go very big, if it loads up here fully.
    Aww, it came in at 1600 x 1069 pixels, still not too bad.
    1990 DSM ISC.JPG
     
    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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  6. We're on Boost

    We're on Boost Proven Member

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    Here’s a pic of my 9 inch extensions to the harness wires.
    Now the plug can reach the ISC position easily.

    The plug here is kind of upside down. The upper 3 wires in the pic are actually wires 4, 5, and 6.

    I used 18 gauge and 16 gauge GXL engine compartment wire,
    parallel connectors (crimp) item number 214305 from Del City,
    heat shrink tubing sizes ¼”, 3/16”, and 1/8”
    a Channel Lock No 909 crimping tool (great tool for generic crimps)
    and a heat gun.

    DSC00293_20.JPG

    ...... and here's a video of the pintle retracting (ignition on) and extending (ignition off) like it should, which was the whole point of swapping wires 4 and 6.



    I finally realized I could rotate the video 90 degrees to make it full screen, so it's full screen now LOL. A little easier on the eyes.
     
    Last edited: Oct 13, 2017
    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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  7. steve

    steve DSM Wiseman

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    The wiring of the ISC coils between 90 and 91 changed at the ECU. On a 90 ISC coil C & D is reversed pins 4 and 6 are swapped relative to the ECU pins on the later cars. ISC pin 4 went to ECU pin 67 and ISC pin 6 to ECU pin 68 on a 90. I always assumed it was a difference in the internal wiring of the old ISC since I didn't notice a difference in the code or operation on my test bed when using a 90 ECU and 91+ ISC but I wasn't looking specifically for it.

    We used to point it out to people swapping to 91+ TB that they needed to swap the wiring when they hooked up the 91+ ISC on a 90 car.
     
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  8. We're on Boost

    We're on Boost Proven Member

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    Steve, Brian, maybe you guys can give me an opinion about something that shows up pretty well in my video. I noticed this first by measuring the pintle position before and after the video. It wasn't the same. It wound up a little more extended at the end than it was initially.

    Sure enough in the video you can see this happen.

    It happens in the first on-off cycle in this series of 4 cycles. The YouTube player shows this really well because you can hover your mouse over the timer bar (with the player on pause) until you see the time you want, click it, and bam it snaps there, still on pause. Or for a 10 second jump you can use the hotkeys L and J.

    So if you snap it to these times, you will see the 5 times that it is in extended position:

    1 sec
    11 sec
    19 sec
    25 sec
    33 sec

    At 11, 19, 25, and 33 sec, the positions are all identical. But in the intial position at 1 sec, it is slightly less extended. If you snap back and forth between 1 sec and 11 sec you will see the difference perfectly. You could run the video to 1 second, then hit the L key, then hit the J key, to jump it back and forth.

    So I’m wondering, is this how it is supposed to act, or is this something weird?

    This is actually the 2nd video I made of this. The first video which I made a few minutes earlier shows the same thing happening.
     
    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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  9. 19Eclipse90

    19Eclipse90 DSM Wiseman

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    I am certainly no expert on electronic devices, but it looks okay to me. One thing I do notice on the video is that the "retract" at 0:01 actually extends first so it knows pretty well where it is and ultimately figures out where it needs to go.
     
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  10. We're on Boost

    We're on Boost Proven Member

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    Yes it does start out (in that first retract) by extending a little, then retracting. I've watched this video frame by frame in a video editor, which is a little better than what we can do at 1/4 speed in YouTube, and sure enough, in this 30 frames per second video, it does spend about 5 frames worth of time going the wrong way there haha!
    I am hoping the same thing you are saying, that maybe this is ok. I'm just going to go ahead and put it all back together and drive/log with it for a while, and see what happens.
     
    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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  11. We're on Boost

    We're on Boost Proven Member

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    On my setup with Magnus intake manifold and Boomba throttle body, the 91+ type ISC interferes with the stock battery shelf.
    Since I’m using a Miata battery anyway I don’t need the whole width of the battery shelf, so I cut it down with a band saw. Took off one leg and left the other leg there with only 1 spot weld.

    This shelf was built like a tank! It was a real battle with my band saw even with removing most of the doublers first by drilling out the spot welds. Looking for a new band saw blade now LOL

    Talon battery tray mod, resized pic.JPG
     
    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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  12. We're on Boost

    We're on Boost Proven Member

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    I got a nice marked up photo today from Boomba support showing the idle set screw on this Evo VIII-IX throttle body. This is what you use instead of a BISS. It does it the old-fashioned way, sets the point at which the butterfly stops just short of completely closed.
    "Search google for this image" doesn't find any photos marked up like this, so for anybody wondering about it, here it is!

    idle set screw on the Boomba throttle body, pic from Boomba support by email 2017.jpg
     
    Last edited: Oct 18, 2017 at 12:04 AM
    My DSM:
    1990 Eagle Talon TSi AWD

    650 whp   510 lb/ft
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