Discussion
Hey Mark
You have mail back!
On old MAF
Pin
A - Low ref
B - IAT Sensor
C - Gnd
D - Voltage Supply
E - MAF Signal
Obviously the favorites are B & C which seems logical, but I just wanted to be sure.
I presume they can be any way round, as the Bosch IAT I have (0 261 231 0060) does not appear to have any markings on it or a diag.
BUT
Now I am not so sure....
Since there was no info with the sensor (bosch IAT), and I did ask Race Tech for something suitable for my specific application, I started to look around..and found that they have a database of info.
... and it mentions a 1000ohm resistor!
The IAT has only 2 pins but no indication what they are (one has the umber 24 stamped on the adjacent plastic)
They use these with data loggers, with 5v (wiv 1000ohm resistor in series) going to one pin that also is analogue output, with the other pin to gnd....... so I have now lost the plot!! :-)
So in that case.. do I need a 5v source with inline 1000ohm resistor, and if so where from? and does it matter which pin cos there is no way I can work out which is which!
What do you think?
You have mail back!
On old MAF
Pin
A - Low ref
B - IAT Sensor
C - Gnd
D - Voltage Supply
E - MAF Signal
Obviously the favorites are B & C which seems logical, but I just wanted to be sure.
I presume they can be any way round, as the Bosch IAT I have (0 261 231 0060) does not appear to have any markings on it or a diag.
BUT
Now I am not so sure....
Since there was no info with the sensor (bosch IAT), and I did ask Race Tech for something suitable for my specific application, I started to look around..and found that they have a database of info.
... and it mentions a 1000ohm resistor!
The IAT has only 2 pins but no indication what they are (one has the umber 24 stamped on the adjacent plastic)
They use these with data loggers, with 5v (wiv 1000ohm resistor in series) going to one pin that also is analogue output, with the other pin to gnd....... so I have now lost the plot!! :-)
So in that case.. do I need a 5v source with inline 1000ohm resistor, and if so where from? and does it matter which pin cos there is no way I can work out which is which!
What do you think?
Edited by 3Dee on Tuesday 27th August 20:01
Ahah!
I found a diag with a similar Bosch IAT which looks identical (but marked 0280 as opposed to my 0260) and the diag shows one pin being 5v and the other signal. Suspect mine will be the same?
So how would I splice this into the MAF wiring? would it be B & D then (if D is 5v????) and do I still need 1000 ohm resistor?
I am somewhat confused as I am a numpty when it come to this sort of thing...
I found a diag with a similar Bosch IAT which looks identical (but marked 0280 as opposed to my 0260) and the diag shows one pin being 5v and the other signal. Suspect mine will be the same?
So how would I splice this into the MAF wiring? would it be B & D then (if D is 5v????) and do I still need 1000 ohm resistor?
I am somewhat confused as I am a numpty when it come to this sort of thing...
Edited by 3Dee on Tuesday 27th August 20:14
Automotive temperature sensors are resistive devices, generally whose resistance falls with increasing temperature (so called Negative Temperature Co-efficient or NTC for short). They usually have a characteristic resistance quoted at 25degC, and generally this is either 2500ohms or 2200 ohms.
The connections on the device are not polarity sensitive, because they are just a resistive element.
However, they are "passive" devices, i.e. they just resist the flow of current driven by a voltage that comes from an 'external' source. For most automotive controllers, the ECU itself includes a "pull up" resistor to an internal 5v rail. This pull up resistor and the NTC sensor itself then forms a potential divider, where the voltage measured on the input pin to the NTC sensor varies with that sensors resistance (and of course, hence with temperature of that sensor).
Now, the value of the pull up resistor (which you usually don't get to see, because it's inside the ecu) is important, because it sets the range of the system. Depending on the resistance range of the sensor, and the temperatures in which you are most interested, the ecu designer can choose different values for the pull up resistor to optimise the measurement range.
So, long story short, do the following:
1) get a digital multimeter, set to the Ohms range (either auto scale, or on say a 10kohm range)
2) get you exisiting MAF, and probe the pins for the Temp sensor (B&C in your case).
3) At roughly room temp (25degC) i'd expect the meter to read around 2500ohms. if it does, great, just connect your new sensor across those same two pins and you're done!
4) If it doesn't read about 2500ohms, report back what it does read and i'll let you know what to do!
(ps. people putting 1k resistors in series with the temp sensors are really just bodging, they are trying to make up for a pull up resistor value in the ecu that doesn't really suit the sensor they are using (too high a value). This works, but leads to a loss of precision as the full voltage range of the ecu's analogue to digital converter will not be being used)
The connections on the device are not polarity sensitive, because they are just a resistive element.
However, they are "passive" devices, i.e. they just resist the flow of current driven by a voltage that comes from an 'external' source. For most automotive controllers, the ECU itself includes a "pull up" resistor to an internal 5v rail. This pull up resistor and the NTC sensor itself then forms a potential divider, where the voltage measured on the input pin to the NTC sensor varies with that sensors resistance (and of course, hence with temperature of that sensor).
Now, the value of the pull up resistor (which you usually don't get to see, because it's inside the ecu) is important, because it sets the range of the system. Depending on the resistance range of the sensor, and the temperatures in which you are most interested, the ecu designer can choose different values for the pull up resistor to optimise the measurement range.
So, long story short, do the following:
1) get a digital multimeter, set to the Ohms range (either auto scale, or on say a 10kohm range)
2) get you exisiting MAF, and probe the pins for the Temp sensor (B&C in your case).
3) At roughly room temp (25degC) i'd expect the meter to read around 2500ohms. if it does, great, just connect your new sensor across those same two pins and you're done!
4) If it doesn't read about 2500ohms, report back what it does read and i'll let you know what to do!
(ps. people putting 1k resistors in series with the temp sensors are really just bodging, they are trying to make up for a pull up resistor value in the ecu that doesn't really suit the sensor they are using (too high a value). This works, but leads to a loss of precision as the full voltage range of the ecu's analogue to digital converter will not be being used)
OK- looks like it is MAF pin A and B not B&C
According to the wiring Diag I have this is Pin A - Low ref and Pin B-IAT
\between these two (and i can now see that these two pins are physically related to each other - and give 3k ohms at workshop temp.
The new Bosch IAT sensor gives a value of 1.72K ohms at workshop temp
So can this be dialled out in the ECM or do I have to add any resistance?
According to the wiring Diag I have this is Pin A - Low ref and Pin B-IAT
\between these two (and i can now see that these two pins are physically related to each other - and give 3k ohms at workshop temp.
The new Bosch IAT sensor gives a value of 1.72K ohms at workshop temp
So can this be dialled out in the ECM or do I have to add any resistance?
Edited by 3Dee on Wednesday 28th August 19:08
3Dee said:
OK- looks like it is MAF pin A and B not B&C
According to the wiring Diag I have this is Pin A - Low ref and Pin B-IAT
\between these two (and i can now see that these two pins are physically related to each other - and give 3k ohms at workshop temp.
The new Bosch IAT sensor gives a value of 1.72K ohms at workshop temp
So can this be dialled out in the ECM or do I have to add any resistance?
Ok, so Low Ref is the 'analogue' zero voltage reference line, and the 0v line on the MAF is the 'power' zero voltage line (keeping them seperate ensures the MAF's power consumption, and resulting resistive voltage drop on the ground wires isn't affecting the sensor signals.According to the wiring Diag I have this is Pin A - Low ref and Pin B-IAT
\between these two (and i can now see that these two pins are physically related to each other - and give 3k ohms at workshop temp.
The new Bosch IAT sensor gives a value of 1.72K ohms at workshop temp
So can this be dialled out in the ECM or do I have to add any resistance?
Edited by 3Dee on Wednesday 28th August 19:08
Basically, the sensors do not have the same temperature characteristic, and without doing at least a 3 point comparison (freezer, room, very low oven) you'll not know how different the curves are. These sensors are not linear btw.
If the shape of the temp/resistance curves are the same (fairly unlikely, but possible) you could just add 1.2Kohm in series with the sensor. If the curve characteristic shape is different, then adding 1.2kohm will only result in a single point where the reported temperature is correct (room temp roughly)
So, if you simply plug in the new sensor, the ecu will report an incorrect air temperature unless you re-calibrate the ecu's lookup table for that sensor (in effect, the table which converts from ADC counts to real units, in this case DegC)
If you need to get the car running in a hurry, i'd just leave the MAF in place and use it as just an IAT sensor!
Edited by anonymous-user on Wednesday 28th August 19:37
Keith,
looked at my Corvette Service Manual.
Pins A and B are used for IAT at the 6.0 litre engines!
The LS7 uses pins D and E to connect the IAT sensor, should both be tan wires.
E is the signal line, D is the low refernce.
I measured approx. 2 kOhms at room temperature.
As Max_Torque said use the IAT sensor in the original MAF to avoid problems.
Michael
looked at my Corvette Service Manual.
Pins A and B are used for IAT at the 6.0 litre engines!
The LS7 uses pins D and E to connect the IAT sensor, should both be tan wires.
E is the signal line, D is the low refernce.
I measured approx. 2 kOhms at room temperature.
As Max_Torque said use the IAT sensor in the original MAF to avoid problems.
Michael
Actually I found out that the pins used by the MAF I have are in fact A&B - (Tan & Tan/White)
And you are right! - The diag I have is from 6ltr version and the loom matches that - this can only mean that the US builder used an engine loom and MAF for the 6ltr version!
However, before I get all knotted up with the builder, it may very well be that in 2007, which is the age of my engine (new at the time), the MAF fitted was the only one available, and got changed later.... I am not sure...
Anyhow, bit academic now, as I have chopped the MAF plug and wired it as per above. I also managed to find a spec for my Bosch IAT with a range of temp/kohms settings, and this has now been dialled into the E38 ECM - so hey-ho...it will be interesting what the result turns out to be.
Thanks for all the pointers chaps... I would not have been able to get where I am now without all your comments and help!
Gad! I love this forum!
And you are right! - The diag I have is from 6ltr version and the loom matches that - this can only mean that the US builder used an engine loom and MAF for the 6ltr version!
However, before I get all knotted up with the builder, it may very well be that in 2007, which is the age of my engine (new at the time), the MAF fitted was the only one available, and got changed later.... I am not sure...
Anyhow, bit academic now, as I have chopped the MAF plug and wired it as per above. I also managed to find a spec for my Bosch IAT with a range of temp/kohms settings, and this has now been dialled into the E38 ECM - so hey-ho...it will be interesting what the result turns out to be.
Thanks for all the pointers chaps... I would not have been able to get where I am now without all your comments and help!
Gad! I love this forum!
3Dee said:
Actually I found out that the pins used by the MAF I have are in fact A&B - (Tan & Tan/White)
And you are right! - The diag I have is from 6ltr version and the loom matches that - this can only mean that the US builder used an engine loom and MAF for the 6ltr version!
However, before I get all knotted up with the builder, it may very well be that in 2007, which is the age of my engine (new at the time), the MAF fitted was the only one available, and got changed later.... I am not sure...
Anyhow, bit academic now, as I have chopped the MAF plug and wired it as per above. I also managed to find a spec for my Bosch IAT with a range of temp/kohms settings, and this has now been dialled into the E38 ECM - so hey-ho...it will be interesting what the result turns out to be.
Thanks for all the pointers chaps... I would not have been able to get where I am now without all your comments and help!
Gad! I love this forum!
I'm not sure if this is relevant but there was quite a few changes in 2008. I know from painful experience the pre 2008 ECU will not work properly with a post 2008 TB as an example. Just be careful where you are taking references from! And you are right! - The diag I have is from 6ltr version and the loom matches that - this can only mean that the US builder used an engine loom and MAF for the 6ltr version!
However, before I get all knotted up with the builder, it may very well be that in 2007, which is the age of my engine (new at the time), the MAF fitted was the only one available, and got changed later.... I am not sure...
Anyhow, bit academic now, as I have chopped the MAF plug and wired it as per above. I also managed to find a spec for my Bosch IAT with a range of temp/kohms settings, and this has now been dialled into the E38 ECM - so hey-ho...it will be interesting what the result turns out to be.
Thanks for all the pointers chaps... I would not have been able to get where I am now without all your comments and help!
Gad! I love this forum!
Paul.B said:
I'm not sure if this is relevant but there was quite a few changes in 2008. I know from painful experience the pre 2008 ECU will not work properly with a post 2008 TB as an example. Just be careful where you are taking references from!
Just to finalise this thread for those interested... new IAT sensor in - all working and calibrated to my ECMhowever having problem with knock sensors.. see dedicated thread
Thanks all!
Gassing Station | Ultima | Top of Page | What's New | My Stuff