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> Cylinder Head Temperature Sensor, 0 280 130 017 Readings
nordfisch
post Jan 29 2021, 11:52 AM
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Hi,
sorry for replying later than supposed...

In the meantime I contacted Volker Huck from jetronic.org and asked him for values of the influence of the CHT resistance to the injection time.
He didn't measure it up to this time. Said he had to do it using the specific ECU-type because they all react different.
But he has the same opinion as we have - the difference between the sensors doesn't matter much because the engine head warms up rapidly in after a short time the sensors show almost the same values then.
He reminded me there are values for the ...017-sensor in the German workshop- manual published by Bosch...

I have to say the values from Bosch are meant without resistor and I tried to read out the values in my chart below from @Superhawk996 's graphic and from his chart.
Please notice the sensor data published by Bosch is at different temperatures for the different sensors.

I think, there is an error in the readings of the first 017 sensor <blue>.
Magnifying the graph, I can see a double line, too... think I corrected the error in my chart.

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Regards
Norbert
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Superhawk996
post Jan 29 2021, 05:52 PM
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QUOTE(nordfisch @ Jan 29 2021, 12:52 PM) *



In the meantime I contacted Volker Huck from jetronic.org and asked him for values of the influence of the CHT resistance to the injection time.
He didn't measure it up to this time. Said he had to do it using the specific ECU-type because they all react different.


@nordfisch

WOW that would be super interesting. Being able to correlate injector pulse time to the CHT with the specific ECU.

It has been documented on the B. Anders site that the 73' ECU is a unique animal so I agree that it would need to be done with the MY73 ECU to get the right result.

What is really interesting to think about is how a 70's vintage ECU gets "calibrated" in an era where that calibration was done by changing the physical analog circuits rather than putting 1's & 0's in memory! (IMG:style_emoticons/default/pray.gif)

Although I do agree there is no practical difference in the sensors once at operating temperature I do have concerns and believe that there is such a significant difference in between 017 sensors and 012 sensors, that the starting, idle and warm-up could be pretty compromised with an 012 sensor in a 73' 2.0L ECU setup. I can't say this for sure as I have yet to assemble my 2.0L engine and to convert it to FI from carbs as I received it. I'm looking forward to trying both sensors though to help solve the riddle.

Next up. I think i have 022 906 041A sensor that is also stamped 0 280 130 017 and yet I believe it reads more like a 012 sensor at ambient temp and cold temps. I need to dig it out and measure it and compare the the 012 curves that have just been documented. I belive there was a period of time where Bosch was transitioning the 1973 017 sensors and mistamped some 012's as 017's.
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Superhawk996
post Jan 30 2021, 10:08 AM
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I missed out on 8 degree F temp this morning. By the time I got my act in gear it was 22F.

I'll keep updating this post as I am able to add lower and lower temperatures as the weather permits.

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Superhawk996
post Jan 30 2021, 10:40 AM
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Just added to other thread on what the CHT resistor looks like so I'll repost here too.

Spec is 270 Ohms and is probably typical +/- 10% to 20% tolerance for non-precision resistors.

Per Brad Anders site he lists them as 1/4 - 1/2 watt whichs seems very plausible given no significant current flows through the CHT sensor itself.

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Olympic 914
post Jan 30 2021, 11:13 AM
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correct me if I am wrong but

I see no reason, other than concours correctness, to use the original resistor instead of any 1/2 - 1 watt resistor of the same size

Presently i do not have the 270 ohm resistor installed on my 2.0 FI with 037 ECU but it would be easy enough to plug one in and see what it does.

Right now my MPS is tuned without the resistor.
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Superhawk996
post Jan 30 2021, 11:24 AM
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QUOTE(Olympic 914 @ Jan 30 2021, 12:13 PM) *

correct me if I am wrong but

I see no reason, other than concours correctness, to use the original resistor instead of any 1/2 - 1 watt resistor of the same size

Presently i do not have the 270 ohm resistor installed on my 2.0 FI with 037 ECU but it would be easy enough to plug one in and see what it does.

Right now my MPS is tuned without the resistor.



You are correct, a resistor is a resistor, is a resitor for a given resistance value. The only thing that really would matter is the power rating.

If you've already tuned your MPS without the resistor and are happy, I wouldn't mess with it.

I'm no D-jet expert but all the research I've done (Anders + other Djet sites) indicates that the analog ECU expects the resitance of the CHT + a 270 ohm offset for these 1973 ECU's.

Overall the end effect of the added 270 ohms on any other ECU (at operating temperature 200F +) would be to make the ECU think its running a bit colder and threfore a bit richer.
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