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Thread: Odd Fire TBI

  1. #16
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    Actually, only one ECM should control the IAC. ECM gets no feedback about IAC position. It only knows what it has commanded for counts. A sticking or unresponsive IAC or in this case, and ecm sending opposite commands, will cause the IAC to move out of synchronization with the ECM's expected position.

    I do not believe I would use only one 5V line. However, the resistance type sensors are part of a resistor network with a terminating resistor in the ecm. Adding a second terminating resistor can alter the total current through the sensor and therefor the voltage reading at the ecm. There are a few people that have published the results of trying to use dual pcm's. I can remember one individual using a 7749 for engine control and a 7427 for trans control in a Syclone and I seem to remember some sensor had to be duplicated. I'll have to see if I can find the information he posted.

    The stock dual plane manifold is divided left and right bank. Each side should have it's own injector. I would expect no trouble with individual bank fuel trim. What would be interesting to me is, after enough time tuning, if VE and/or spark tables end up slightly different between L and R banks.

  2. #17
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    Quote Originally Posted by 1project2many View Post
    Actually, only one ECM should control the IAC. ECM gets no feedback about IAC position. It only knows what it has commanded for counts. A sticking or unresponsive IAC or in this case, and ecm sending opposite commands, will cause the IAC to move out of synchronization with the ECM's expected position.

    I do not believe I would use only one 5V line. However, the resistance type sensors are part of a resistor network with a terminating resistor in the ecm. Adding a second terminating resistor can alter the total current through the sensor and therefor the voltage reading at the ecm. There are a few people that have published the results of trying to use dual pcm's. I can remember one individual using a 7749 for engine control and a 7427 for trans control in a Syclone and I seem to remember some sensor had to be duplicated. I'll have to see if I can find the information he posted.

    The stock dual plane manifold is divided left and right bank. Each side should have it's own injector. I would expect no trouble with individual bank fuel trim. What would be interesting to me is, after enough time tuning, if VE and/or spark tables end up slightly different between L and R banks.
    i am going to use 1ECM for the IAC control, but I wonder about feedback. If there is no feedback why does each winding in the IAC have its own return wire back to the ECM instead of sharing 1 Wire. We all know that the GM doesn't add unnecessary wires if they can get by without it. Just think how much money they can save by deleting that wire.(Hah).As far as getting the proper sensor reading I'm going to bench test them all and verify that the readings are within the required parameters for proper ECM operation.
    Craig
    Last edited by Willys43; 03-07-2016 at 08:07 AM.

  3. #18
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    Here are a couple of questions I have.
    1. Does the ECM read sensor voltage or current
    2. Why does the MAP and the TPS have the extra ground wire
    3. Which way does the current flow thru the CTS/ECT? Neg to Pos? What should the resisted value parameters be?
    4. I have read there is a 5 volt ref signal output from ECM to ECT, but that doesn't make sense to me. I Am unaware of how the ECM would be able to read the resisted value

  4. #19
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    1P,
    Thought you might be interested to hear the even bank went dead again. I checked the spark with the timing light and still had good clean spark, on the even wires. I went and got the pump spray bottle with gasoline and shot a couple of pumps into even bank of carb, "Viola" the even bank runs again. I went and ordered a carb kit cause something is plugged up tight.
    Craig
    Last edited by Willys43; 03-07-2016 at 08:41 AM.

  5. #20
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    Quote Originally Posted by Willys43 View Post
    Here are a couple of questions I have.
    1. Does the ECM read sensor voltage or current
    2. Why does the MAP and the TPS have the extra ground wire
    3. Which way does the current flow thru the CTS/ECT? Neg to Pos? What should the resisted value parameters be?
    4. I have read there is a 5 volt ref signal output from ECM to ECT, but that doesn't make sense to me. I Am unaware of how the ECM would be able to read the resisted value
    1) ECM will monitor voltage.
    2) Extra? Both of those sensors can be thought of as potentiometers. The 5V reference is "split" between ground and the signal wires. When the resistance between the signal wire and power is high, the signal voltage is low. When resistance between 5V and signal is low, signal voltage is high. Open the ground circuit and the signal line will go to near 5V.
    3) Hmmm... Current always flows from negative to positive (although many of us were taught otherwise in school). There are charts on the internet and in the factory service manual which match up resistance to temperature.
    4) The ecm reads the voltage on the positive wire to CTS. As the resistance through the sensor changes so does the voltage between the supply line and ground. Both the two and three wire sensors require a roughly equivalent strategy for the ecm to detect voltage sensor. The temp sensor is only two wires due to the nature of the sensor.

    If there is no feedback why does each winding in the IAC have its own return wire back to the ECM instead of sharing 1 Wire.
    The ecm needs to be able to switch the direction of current flow through each coil in order to make the motor work in both directions.

    Just think how much money they can save by deleting that wire.
    They've gone to low voltage for many circuits today and tried to combine as many control circuits as possible with CAN communications. They're running things so tight that we see problems with terminal overheating and connector failure when a component draws just 2-3A over specification!


    I went and ordered a carb kit cause something is plugged up tight.
    That there is some baaad luck.

  6. #21
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    Quote Originally Posted by 1project2many View Post
    1) ECM will monitor voltage.
    2) Extra? Both of those sensors can be thought of as potentiometers. The 5V reference is "split" between ground and the signal wires. When the resistance between the signal wire and power is high, the signal voltage is low. When resistance between 5V and signal is low, signal voltage is high. Open the ground circuit and the signal line will go to near 5V.
    3) Hmmm... Current always flows from negative to positive (although many of us were taught otherwise in school). There are charts on the internet and in the factory service manual which match up resistance to temperature.
    4) The ecm reads the voltage on the positive wire to CTS. As the resistance through the sensor changes so does the voltage between the supply line and ground. Both the two and three wire sensors require a roughly equivalent strategy for the ecm to detect voltage sensor. The temp sensor is only two wires due to the nature of the sensor.


    The ecm needs to be able to switch the direction of current flow through each coil in order to make the motor work in both directions.


    They've gone to low voltage for many circuits today and tried to combine as many control circuits as possible with CAN communications. They're running things so tight that we see problems with terminal overheating and connector failure when a component draws just 2-3A over specification!



    That there is some baaad luck.
    It's what you get buying something that has been sitting for five years

  7. #22
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    That's what you get when you buy a 72 year old vehicle with a 54 year old engine that's been sitting in abarn for 5 years. Almost 0 rust, I'll fix the problems. I don't think I've ever seen a potentiometer that wasn't sitting on a metal frame, that's why I didn't understand the extra wire, and the voltage split.

  8. #23
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    Couldn't the ECM reverse the direction of current flow even if the windings had a common ground?
    Is the 5 volt ref positive or negative?
    If car mfg is anything like building construction the standards have changed so much in the past 30 years? Because of better and more engineering the the materials we used keep getting lighter and lighter yet carrying the same load.

  9. #24
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    I don't think I've ever seen a potentiometer that wasn't sitting on a metal frame, that's why I didn't understand the extra wire, and the voltage split.
    http://fddrsn.net/pcomp/examples/potentiometers.html
    Potentiometer and description of operation. A would be 5V, B would ground, W would be connected to the signal.
    This is exactly what a TPS is. For basic understanding you can think of a MAP as being the same thing.

    Couldn't the ECM reverse the direction of current flow even if the windings had a common ground?
    Yes, it could be done that way with added complexity. GM has chosen to isolate both ends of the stepper motor coil.

    Is the 5 volt ref positive or negative?
    It is positive.

    Because of better and more engineering the the materials we used keep getting lighter and lighter yet carrying the same load.
    Exactly. The 2015 and up F150 is primarily aluminum.

    That's what you get when you buy a 72 year old vehicle with a 54 year old engine that's been sitting in abarn for 5 years.
    If that's the only surprise then you've got a good rig.

  10. #25
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    That's how I thought they worked for allowing the signal voltage, I just didn't realize that the remainder of the ref voltage went to ground. That was an excellent description. What confuses me is that the direction of current travel seems backward.
    Is the W - or +?
    Last edited by Willys43; 03-08-2016 at 05:37 PM.

  11. #26
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    may i ask why 2 ecus as far as i know there is a buick oddfire hei type reluctor dizzy availiable that could run the gm 8 pin ignition module and one ecu

  12. #27
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    What confuses me is that the direction of current travel seems backward.
    Is the W - or +?
    Well, now, that's a fine question. The ecm measures between W and GND so the voltage it sees will never be negative. But it could look negative if you measure between 12V and W. This measurement would show higher resistance if the wiper is at the +5V side of the pot, and it would show a full 12V when the wiper goes to ground.

    why 2 ecus as far as i know there is a buick oddfire hei type reluctor dizzy availiable that could run the gm 8 pin ignition module and one ecu
    oddfire engine has unequal pulse times between cylinders. ECM calculates rpm based on number of cylinders and time between reference pulses. Varying time between pulses would work out to rapidly increasing and decreasing RPM.

  13. #28
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    "Look negative" wow that's loaded. I thought the ECM measured between W and the 5 volt ref? If the ECM measures between W And Ground, why the ref voltage.

    Delco,
    If you'll look at the Willys43 introduction thread, you will see how and why we ended up with 2 ECMs
    Craig
    Last edited by Willys43; 03-09-2016 at 05:15 PM. Reason: bad grammer

  14. #29
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    If the ECM measures between W And Ground, why the ref voltage.
    Measuring between REF and GND gives a "known" or reference voltage. Second measurement between W and GND gives signal voltage. Then ECM can be programmed with max and min allowed values so if signal = REF or signal = GND a code is set.

  15. #30
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    OK, then is the ref signal basically for comparison purposes to allow the ECM to calculate a corrected voltage for when then system voltage varies?

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