Yes, do it that way. The ECM keeps track of the IAC position so having 2 ECMs on the same IAC will unsync the IAC from the position each ECM thinks it is at. That is assuming both ECM's can move it at the same time. Drive both coils at the same time and it won't even move.
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.Originally Posted by 1project2many
Craig
Last edited by Willys43; 03-07-2016 at 06:07 PM.
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.
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.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.
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!Just think how much money they can save by deleting that wire.
That there is some baaad luck.I went and ordered a carb kit cause something is plugged up tight.
It's what you get buying something that has been sitting for five years
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.
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.
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 06:41 PM.
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