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Sharing temp sensors between EEC and MegaSquirt 

 

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 Post subject: Sharing temp sensors between EEC and MegaSquirt
Posted: Tue Oct 18, 2005 4:40 pm 
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I found that page that I'd read which talks about sharing the sensors.

http://www.megasquirt.info/v22manual/sharesen.htm

I'm guessing we could do this? provided the EEC doesn't change bias resistors??

I dont really understand what its saying (really need to read it slowly and carefully) but anyone interested in doing this? :P

How should us MS'ers go with sharing other sensors.. (namely O2, TPS?)?

Can we just splice into the wire and read them?
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Posted: Tue Oct 18, 2005 5:39 pm 
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Feel free to correct me anyone,

Basically, the sensor is a resistor.. the EEC sends 5 volts through it, and reads what is on the other side (in the middle actually)... If you hook up to the same resistor the megasquirt, it will be sending another 5 volts (its not the voltage that matters but). The problem is, they are both drawing current, and resistance is based on current and voltage.. increase current, and the voltage is decreased (I think), could be increased.. Im think R = V/I.. anyway, not in the mood for rearranging.

So basically you will get an incorrect reading, thats why you need to set up a resistor, to basically "level" it out.

How's that?

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Posted: Tue Oct 18, 2005 5:40 pm 
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And also not to mention, if they suck enough current through the thing, it would fry the TPS...


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Posted: Wed Oct 19, 2005 10:39 am 
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Well,

With the TPS for example, it has 3 wires. VREF (+5V), GND, Signal.

The EEC handles VREF and GND while i'd just be splicing into the Signal wire to read into the MS. Both ECU's would probably just need recalibrating.

The O2 sensor, i would assume the same, as one can hook up a gauge to it without affecting the ECU.

The temp sensors are different though... within the ECU they have a resistor thats acts as a voltage divider combined with the coolant/ambient temp. Apparently removing the bias resistors in the MS will allow the two to share as the MS will just be reading the voltage.

The only thing is you have to work out what the bias resistor in the EEC is, which is documented on the MS site... http://www.megasquirt.info/v22manual/sharesen.htm
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Posted: Wed Oct 19, 2005 7:34 pm 
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has any one done this to a ef yet or does any one know if ford have one bias resistor or 2 ?

 

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Posted: Wed Oct 19, 2005 10:35 pm 
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fords have one bias resistor AFAIK.
You have a point on the 02 sensor glenneaux. As far as the TPS sensor goes, the measurment needs to be done on the middle with reference to ground, so try it, and it should be fine (from what I gather anyway), just make sure both are definate 5V Vref.


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Posted: Wed Oct 19, 2005 10:42 pm 
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well a 02 sensor creates its own voltage, the ecu doesnt send down 5 volts to it, so u can splice into that.
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Posted: Wed Oct 19, 2005 10:47 pm 
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yeah, the 02 isn't a problem.
And for the TPS, its as much a variable resistor as the rest. So, I was assuming that the same needed to be done for it, but on the other hand if you reference the signal wire correctly, and don't feed another 5V into it, should be fine. (I think).


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Posted: Thu Oct 20, 2005 8:46 am 
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If the auto doesn't rely too heavily on engine temps, you could always just take the sensors for the MS and put a resistor in the circuit for the EEC so it always gets a reading of say 20C for air and 80C for water.
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Posted: Thu Oct 20, 2005 8:51 am 
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justfordima wrote:
yeah, the 02 isn't a problem.
And for the TPS, its as much a variable resistor as the rest. So, I was assuming that the same needed to be done for it, but on the other hand if you reference the signal wire correctly, and don't feed another 5V into it, should be fine. (I think).


Cheers


As long as you just tap into the signal wire, then the voltage that each ECU sees should be the same as the ECUs would be in parallel, which means voltage stays the same, but current is shared among the devices, but sinve current has nothing to do with the TPS, it doesn't matter.
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Posted: Thu Oct 20, 2005 9:56 am 
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unclewoja wrote:
If the auto doesn't rely too heavily on engine temps, you could always just take the sensors for the MS and put a resistor in the circuit for the EEC so it always gets a reading of say 20C for air and 80C for water.


Agreed. Glenneaux, i assume MS will be controlling the thermo fans... but i am unsure of the architecture regarding coolant temp readout on the dash... if this is part of the data output from EEC to the dash then you'll probably want EEC to be able to read the CLT sensor... unless you are happy to use megatune for engine temp readings??

 

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Posted: Thu Oct 20, 2005 10:09 am 
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4.9 EF Futura wrote:
unclewoja wrote:
If the auto doesn't rely too heavily on engine temps, you could always just take the sensors for the MS and put a resistor in the circuit for the EEC so it always gets a reading of say 20C for air and 80C for water.


Agreed. Glenneaux, i assume MS will be controlling the thermo fans... but i am unsure of the architecture regarding coolant temp readout on the dash... if this is part of the data output from EEC to the dash then you'll probably want EEC to be able to read the CLT sensor... unless you are happy to use megatune for engine temp readings??


--edit

Its an EB so i have clutch fan.. no computer control of fans..

--
Well. I'd prefer the dash reading to still work seeing as its on the dash and always visible ;) (yes i'm paranoid about overheating my I6!!)

The reason to keep temp sensors connected is i won't be doing spark control YET (not doing turbo YET either). So i'd prefer the EEC to be getting correct readings.

This weekend i'm gonna investigate as per that document and hopefully i should just be able to splice into it...

My preferences to these options would probably be:

1) Share sensors
2) Install extra sensors somewhere
3) Disconnect sensors from EEC and hook up dummy resistors.
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