gone_fishin
Member
- :
- One of a Kind '99
Need some help from anyone that's familiar with protege (and specifically the MSP) electronics.
I'm getting some various wiring discrepancies sorted out from my swap which have been bothering me for quite some time. They pertain to the instrument cluster. Instead of swapping dash harnesses, I've done my own custom wiring. The swap was a fullout '03 Mazdaspeed protege drive and power train dropped into my 1999 1.8 liter ES.
Engine coolant temperature (ECT) sensors 101
In addition to the differences between the MSP engine coolant temperature (ECT) sensor itself and the 1999 1.8 ECT sensor, there are wiring differences among both applications in the ways in which they link to the PCM and instrument cluster. For those who aren't familiar with OBD-II thermistors, an ECT sensor (a thermistor) will resist current flow variably depending upon temperature. Lower temperatures increase resistance (measured in Ohms), whereas higher temperatures lower resistance. The PCM determines the resistance by reading how much voltage is returned to the PCM terminal after the 12-14V is initially supplied to the thermistor. A large ammount of returned current tells the PCM that the engine is cold. Analogously, a small ammount of returned current tells the PCM that the engine is hot. Accordingly, the PCM will advance/retard timing, enrich/enlean the fuel mixture, etc. to compensate for temperature change. Thermistors therefore have what is called a resitance profile-- a graph of resistance (in Ohms) with respect to engine temperature (Degrees Celcius/Farenheit).
Now my Question
Due to differences in the thermistor circuitry in the MSP ECT sensor versus the 1999 1.8 ECT sensor (in how signal is outputed to the instrument cluster), I need to swap in the '99 ECT sensor in for the MSP ECT sensor if I want to keep the existing gauge cluster. However, I'm nervous about swapping them out. Why? Because the resitance profiles are slightly different. How different? See Below:
Mazdaspeed Protege
Water Temp (deg. F)_____|_______Resistance (kilohm)
68_____________________|_____________________2.2-2.6
176____________________|_____________________0.29-0.34
1999 1.8 Liter Protege ES
Water Temp (deg. F)_____|_______Resistance (kilohm)
68_____________________|_____________________2.2-2.8
176____________________|_____________________0.29-0.40
---------------------------------------------
This difference of 200 ohms at 68 degrees F (cold) and 600 ohms at 176 (hot) I'm assuming would cause the FS to run slightly hotter. How major or minor is this difference? Is it negligable? Could it have potentially serious consequences with a turbo motor?
I'm getting some various wiring discrepancies sorted out from my swap which have been bothering me for quite some time. They pertain to the instrument cluster. Instead of swapping dash harnesses, I've done my own custom wiring. The swap was a fullout '03 Mazdaspeed protege drive and power train dropped into my 1999 1.8 liter ES.
Engine coolant temperature (ECT) sensors 101
In addition to the differences between the MSP engine coolant temperature (ECT) sensor itself and the 1999 1.8 ECT sensor, there are wiring differences among both applications in the ways in which they link to the PCM and instrument cluster. For those who aren't familiar with OBD-II thermistors, an ECT sensor (a thermistor) will resist current flow variably depending upon temperature. Lower temperatures increase resistance (measured in Ohms), whereas higher temperatures lower resistance. The PCM determines the resistance by reading how much voltage is returned to the PCM terminal after the 12-14V is initially supplied to the thermistor. A large ammount of returned current tells the PCM that the engine is cold. Analogously, a small ammount of returned current tells the PCM that the engine is hot. Accordingly, the PCM will advance/retard timing, enrich/enlean the fuel mixture, etc. to compensate for temperature change. Thermistors therefore have what is called a resitance profile-- a graph of resistance (in Ohms) with respect to engine temperature (Degrees Celcius/Farenheit).
Now my Question
Due to differences in the thermistor circuitry in the MSP ECT sensor versus the 1999 1.8 ECT sensor (in how signal is outputed to the instrument cluster), I need to swap in the '99 ECT sensor in for the MSP ECT sensor if I want to keep the existing gauge cluster. However, I'm nervous about swapping them out. Why? Because the resitance profiles are slightly different. How different? See Below:
Mazdaspeed Protege
Water Temp (deg. F)_____|_______Resistance (kilohm)
68_____________________|_____________________2.2-2.6
176____________________|_____________________0.29-0.34
1999 1.8 Liter Protege ES
Water Temp (deg. F)_____|_______Resistance (kilohm)
68_____________________|_____________________2.2-2.8
176____________________|_____________________0.29-0.40
---------------------------------------------
This difference of 200 ohms at 68 degrees F (cold) and 600 ohms at 176 (hot) I'm assuming would cause the FS to run slightly hotter. How major or minor is this difference? Is it negligable? Could it have potentially serious consequences with a turbo motor?
