2000 EFI (MM) Ultra Classic

I want to connect my engine temperature sensor to a data logging system.

for that data to be useful, I need to know the output voltage for the full operating range of the sensor but the service manual only lists the output voltages up to 230* F. Since the idle speed controller doesn't reach zero stops until 285* F, and this is the only engine temperature sensor on the bike, I have to believe the sensor continues to send calibrated data at least as high as 285*. Because this is a thermistor, it's output is not linear so I can't just extrapolate the data for higher temperatures.

Anyone have this data or know where I can get it??

Thanks in advance.

 

that's one for Ed or Steve.
m

 

i would have to take a look-see, but

i believe the hd uses a thermo resistor that changes resistance as the temp rises, i believe it to be less resistance. that said, it will not output any voltages.
now if it were a thermo-couple, then you could get the range vs temp easily once you know the type as there are many.
the hd system does not need to know temp to the degree, only if it is hot enough to switch to diff program schedules. inside the ecu are comparator circuits that feed a certain amount of current to ground via the resistor, and another resistor that operates in a by-pass mode along with it and the ecu looks at the voltage drop across this resistor and decides what to do. if you have a temperature gauge, it too is calibrated to read this voltage drop to a certain numerical reading on the face of the gauge.
now this does not stop you from adding your own thermo-couple.


from fsm electrical
Engine Temperature (ET) Sensor
The ET sensor is a thermistor device, which means that at a
specific temperature it has a specific resistance across its terminals.
As this resistance varies, so does the voltage.
• At high temperatures, the resistance of the sensor is very
low, which effectively lowers the signal voltage on ECM
[78] terminal 6.
• At low temperatures, the resistance is very high, allowing
the voltage to rise close to 5V. The ECM monitors this
voltage to compensate for various operating conditions.
The ECM also uses the sensor input as a reference for
determining Idle Air Control (IAC) pintle position.

 

Thanks Buster, I've got the manual and read all that as well as the chart that shows the output voltages up to 230*. The problem is, the ECM must rely on this sensor up to at least 285* since that's when the ECM moves the ICS to zero stops, and it would need input from an engine temp sensor to know when the engine reach 285 to do that. What I'm looking is the chart for the full range of sensor output voltages, not a chart that ends at a lower output than the sensor is used for.

 

that is just that, the thermistor changes resistance, not voltages. the voltage across this circuit is internal to the ecu. if you were to try and do an add-on, you could load the circuit and then skew the entire circuit to rubbish for the ecu.
case in point: the O2 sensor can be checked with a vom but it MUST have at least 10 times the resistance than the circuit being tested. you probably could get by with one meg ohm but more would be better. what happens is you place another circuit, the meter in this case, in parallel so now there is current through the meter and the O2 circuit. this will skew the output to the ecm.
the ecu does not care what the temp is, ONLY resistance. if you were to test this circuit, hd gave approximate temperature, these will not be as accurate as a thermocouple.
if you want, you could map it out with an accurate 5 volt source and a controlled heating chamber, but chances are, will not be the same as what the ecu sees.
another point is, there is a limited amount of current sent to the thermistor by a driver and if you over-load the driver, guess what, you will toast the circuit. better to be safe and add a thermocouple.
comparator compares one analogue voltage level with another analogue voltage level, or some preset reference voltage, VREF and produces an output signal based on this voltage comparison. I

 

Buster, I think I understand what you're saying and I agree with part of it in theory, and I think I see another part of it differently.

Where I don't think we agree is what the ECM is measuring. If I understand you correctly, you're saying that the ECM directly measures the variable resistance of the sensor's thermister as it is effected by changing temperatures. As I understand it, the ECM doesn't measure this resistance, but rather measures the effect of this resistance on the 5-v signal as "Input" from the ECM. The "Output" voltage of the sensor varies based on the resistance of its internal thermister, which varies with engine temperature. Thus, the ECM, per the chart below, sees an output voltage in the range 0.4v to 4.5v from the sensor output and adjusts various operating parameters accordingly.

I agree that by adding an additional load to the circuit - in my case, both the data logging rig and the wire leading from it to the place I tap into the circuit - will reduce the circuit voltage seen by the ECM. The question, in this case, is: Will this additional load be enough to cause an undesirable effect on the operation of the ECM as it uses this data?

Considering that the MoCo states the engine temperature sensor output voltage is only accurate to +/- 20%, there's a good chance that the small additional load will have no impact at all, but I can't say for sure and my dc theory is rusty enough that I'd have to research how to do the math.

Where is it that you propose I add the thermocouple? The only concern I have about that is, if it's not measuring at the very same place on the head that the engine temperature sensor measures, then its reading may be far enough off as to be useless if I'm trying to understand what the engine temperature is in the eyes of the MoCo. For understanding what is hot in the eyes of the MoCo, then the only truely valid place to measure is where they measure.

Thanks for taking to the time to engage in this discussion!

 

I couldn't get this chart to load with the previous reply, so I posted another.

 

i think i found out where to get a range from IF they will do so. they are in a diff time zone so will call them later. not sure if they make it for hd or not but the sensor is a direct replacement.
the hd ecu is dumbed down and does not operate like a modern car. it is all about $$$. have you tried using the data stream as a tap since the ecu probably uses an analog to digital converter circuit and reading off the data stream will not load the sensor.
it is a very complicated process to size a thermistor to a temp range, reason why thermocouples work better although thermistors are very accurate.

the ecu does not measure resistance only the effects of it. since the driver is limited, as more current goes to ground, the voltage drops. the only thing you can get from a thermistor is resistance readings, has no ability to output any voltages.

 

Not sure what you mean by data stream. My plan is to tap the "voltage out" in the harness between the ECM and the ETS, a couple inches behind the sensor, and run a 16-awg wire from there to my data logging equipment within my fairing.

Thanks in advance for looking into this with the manufacturer!

 

sent you a pm, i have the chart
however, looking at the numbers, it seems that you will run out of voltage range so i do not think the ecu will be able to extract any info, this is a typical lower number for a 5 volt system of approx .5 volts. perhaps your data logger might but at .5 volt, will not take much to load the circuit. anywho, hope it works out.