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Resistors for Auto ECU 

 

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 Post subject: Resistors for Auto ECU
Posted: Sun Jun 26, 2005 12:56 pm 
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Just a couple of quick questions.

I've just pulled out my manual ED XR6 ECU (cries) and put in an EL Auto one, so now I need to put some resistors in.
I know to use a 1.2K resistor on the trans temp line, and 7K resistor for the transmission position.
I want to put these in at the wiring harness at the ECU, so do I put the resistors between the relevant pin (say 42 for trans temp & 30 for trans position) and signal ground (pin 46) or to 12v (pin 1).

Cheers.

 

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Posted: Sun Jun 26, 2005 1:50 pm 
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They would be voltage inputs so you should use a 12v supply. You are just trying to output the correct voltage so the EEC thinks everyting is normal.
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Posted: Sun Jun 26, 2005 6:16 pm 
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You need a pair of voltage dividers, each made up of two resistors.

For each divider you need two resistors in series. One of the outside legs needs to go to the reference voltage source, 5v (terminal 26 on the EL). The other outside leg goes to ground. Where the resistors are connected, the inside legs, goes to the ECU.

To show the transmission is in D you need 2.5V at the ECU. For this divider you need two resistors of the same value, about 1K would be a good start. The gear position sensor is terminal 30 on the EL.

For the transmission you need anywhere between 1 and 3.6 volts so you might as well use the 2.5V and only have one divider. The transmission temp is terminal 42 on the EL.

Basically your circuit will look like this:

t26
|
\
/ 1K
\
/
|
+ t30 and t42
|
\
/
\ 1K
/
|
Gnd t46

 

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Posted: Sun Jun 26, 2005 6:47 pm 
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Ahhh thanks heaps been swearing at it for not working.

If I want to tell it its in neutral (3v) what do I use?

 

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Posted: Sun Jun 26, 2005 10:29 pm 
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Ahh I see what's going on I think.

If I wanted 3V for both would this be right?

t26 (5v)
|
\
/ 2K
\
/
|
+ t30 and t42
|
\
/
\ 3K
/
|
Gnd t46


Anyway, what's with the 1.2k and 7k resistors? Where were these established from lol?

 

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Posted: Sun Jun 26, 2005 11:58 pm 
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Yup, thats it.

I don't know where you got the 1.2K and 7K from, nothing I have ever posted I don't think.

 

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Posted: Mon Jun 27, 2005 12:06 am 
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raiki wrote:
Yup, thats it.

I don't know where you got the 1.2K and 7K from, nothing I have ever posted I don't think.


Oh there's just heaps of threads (I think) that mention using those values. But I think they are plugging them straight into the cannon plug in the enigine bay.

So your sure this method will work? Hope so, sick of hearing the fans :)

 

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Posted: Mon Jun 27, 2005 10:43 am 
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Nope, I am not entirely sure. It is just what I worked out in my head after reading your post.

Thinking about it the ECU will supply the power and the first part of the divider so perhaps all you need are resistors to ground on each pin. I'll have another look tonight.

 

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Posted: Mon Jun 27, 2005 3:34 pm 
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What I have recommended will definately work for the gear position sensor. Temperature I am not sure about. The trick will be to measure the voltage at the pin for the temp input. If you are measuring 5v you will need a resistor to ground for the replacement. Try a few values until you get about 2.5v at the pin. If you try 1K and get a voltage you can figure out the bias value and then calculate the resistor you will need.

 

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Posted: Wed Jun 29, 2005 9:10 pm 
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Any confirmation on how this temperature thing works anyone?

My multimeter is up to s**t, I can't be 100% sure its working :(

 

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Posted: Thu Jun 30, 2005 12:51 am 
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#1 tool to have before you start messing with your ECU, a working digital multimeter. Without it you are going to blow something up.

Get another meter and do what I suggested in my last post, guaranteed to work.

 

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Posted: Thu Jun 30, 2005 1:57 am 
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the resistors I used were the 1.2k and the 7k, and I plugged them into the cannon plug in between the two terminals, obviously this is achieving the same thing. As the sensor is a variable resistance sensor, it has voltage going in, and resistified(does that word exist?) voltage coming out, feeding the ECU the new reading, letting the ECU know what's going. Hence a solid resistor of a set value works instead of the variable resistor that was there in the first place (just further down), so you'll need to find the pin which tells the ECU the signal, and use the supply voltage, Im assuming its 5V. So feeding 5V into a resistor, and then into the needed terminal. So what raiki is saying in theory is right. The values I can't confirm on though.


Cheers

 

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Posted: Fri Jul 01, 2005 2:26 pm 
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justfordima wrote:
the resistors I used were the 1.2k and the 7k, and I plugged them into the cannon plug in between the two terminals, obviously this is achieving the same thing. As the sensor is a variable resistance sensor, it has voltage going in, and resistified(does that word exist?) voltage coming out, feeding the ECU the new reading, letting the ECU know what's going. Hence a solid resistor of a set value works instead of the variable resistor that was there in the first place (just further down), so you'll need to find the pin which tells the ECU the signal, and use the supply voltage, Im assuming its 5V. So feeding 5V into a resistor, and then into the needed terminal. So what raiki is saying in theory is right. The values I can't confirm on though.


Cheers


Just for reference for anyone searching in future, I've confirmed a 7K2 resistor will also work aok in the engine bay plug.

I state this because I had no luck whatsoever finding an actual 7K resistor - but any d**k Smith will carry 7K2 (I've confirmed 7K5 will NOT work and I haven't tried 6K8).

This is for fooling the ecu into thinking auto trans is in neutral - the resistor is put across the terminals directly opposite the connector "latch" (ie. as opposed to the ones "adjacent to" or right next to the latch - you want the ones on the opposite side of the connector).

Anyone with no clue about resistors (like me) - just go to d**k Smith and ask for "a 7K2 ohm resistor please - low wattage is ok because it's just for signal into a computer". Cost is about 20c for a few of them.

7K ohm = 7000 ohm
7K2 ohm = 7200 ohm

 

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Posted: Fri Jul 01, 2005 5:55 pm 
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The trans temp is a 5v output it turns out.

I'll need a fairly large value resistor to get it down to 2.5v won't I, something like 1000k?

I don't see why there would be different values needed when plugging into the cannon plug.
WTF is the go.

 

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Posted: Fri Jul 01, 2005 6:39 pm 
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Arrrgh scrap that. Turns out its been right for a few days how I have it now.

The voltage between Pin 30 and Pin 46 is 3v with engine running, and voltage between Pin 42 and Pin 46 is 2.7v.

So that's all in order, but thermos are still running for some reason. Must be a bad connection.

 

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