using aftermarket temp. sensors on 7427 ecm's

[grumbolt]

Well, there's some good news and some bad news and some good news with work.

The good news is that the coolant temp, air temp, and transmission temp sensors are not linear. These sensors all require a table (actually two tables for coolant and transmission temp) to convert the sensor reading into the correct value. In theory you should be able to enter the correct temperature values from your sensor and the ecm will use the lookup table to get the correct reading.

Now here's the bad news: GM uses the same lookup tables for both coolant temp and transmission temp. So if you change them you will get the correct temp from the trans sensor and the wrong temp from CTS.

The easiest answer might be to build new lookup tables and add them to an unused area in the chip. But that requires a little bit of coding skill. Another option may be to direct the IAT to use the CTS tables and to direct the TFT to use the IAT table. But the IAT table is very rough... there are maybe 5-10 values? Where the CTS/TFT tables are 256 byte tables.

You might also be able to design a "best fit curve" that approximates the transmission temperature sensor values. We were able to do something like this for Tunerpro once we realized the conversion formula for CTS was producing errors. You may need to use a tool such as Excel to generate the formula then replacing the table lookup routine with the forumla. Proabably not as easy and not likely to be as accurate as creating new tables.

A/D to Temp conversion tables are found at 0xF8eF and 0xF9EF. Transmission temp lookup and conversion begins at 0xC6F6.

Good luck.

just a thought..... if i leave all the tables the same and use a bench setup to determine what temp the ecm "thinks" 160 degrees is. (lets say when the probe is at 160 degrees the ecm thinks it is at 300 degrees) couldnt i simply set the parameters in the fan mod to turn on at 300 instead of 160? i am only using the ecm to control the motor, the transmission is stand alone, and i am not even using TCC at this time. and if i do use tcc in the future, it will not be controlled by the ecm.

honestly the coding is way over my head, i want to learn but that is going to be a long process lol... i dont know what the different commands are much less how to set up the tables into a usable format. i am very thankful for you guys that have pioneered the way for guys like me to be able to tune our toys without knowing the ultra technical coding stuff, we only have to learn the highly technical tuning stuff lol..

thanks again for your help..
grum