Odd Fire TBI

**Willys43** · 03-07-2016

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

**1project2many** · 03-07-2016

Originally Posted by Willys43

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.

**Willys43** · 03-08-2016

Originally Posted by 1project2many

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

**Willys43** · 03-08-2016

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.

**1project2many** · 03-08-2016

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.

**Willys43** · 03-09-2016

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 +?

**delcowizzid** · 03-09-2016

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

**Willys43** · 03-08-2016

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.