Coolant Temp Sensor Calibration

The 1UZFE EGR Delete Kit is available for sale here.

P Bateman

Something I've found recently that should be shared...

When setting up aftermarket ECU, there are often pre-configured tables you can use to align your coolant temp sensor reading with the actual temperature - effectively teaching the ECU how to read the sensor. In the case of a Haltech, you only get the choice of pre-configured tables for Toyota 1FZ-FE Coolant Sensor or Toyota JZX100 Coolant Sensor. You would think that, being Toyota as well, a 1UZ-FE Coolant sensor would be within range of one of these, but the readings I got were very wrong. Both of them had the dash reading 115 degrees with the fan running constantly. A pyrometer confirmed the sensor was much cooler.

Solution: I found a few charts in Toyota workshop manuals that gave the resistance range for the coolant temp sensor at -20, 0, 20, 40, 60, 80 and 100 degrees. After examining it carefully, I was able to map out the upper and lower resistances for each temperature range - and from that, determine the averages. With these average numbers programmed into the sensor calibration, it reads properly now and this is confirmed with the pyrometer.

I also wanted it to measure temperature up to a theoretical 120 degrees in 10 degree increments, so with a bit of simple maths, I filled the gaps in between. Here are the results (in KiloOhms).

Coolant Tempt Sensor Calibration.jpg

I would be interested to know what others have used in their setup and how accurate the readings are.

This content is only for after market ECUs.
I also share your concerns about sensor calibration. The config values for my Engine TS and Air TS were provided by the ECU supplier as part of a start map, have never been changed and formed part of a number of dyno tunes to what I have today. Are they accurate... well they don't seem to be too far out. However there is another parameter that also falls into the dark arts of ECU config and tuning. One that has bugged me for sometime is injection timing. Or sequencing as its called in my ECU config. There are very few write ups that I have found that offers some real scientific facts, physics and advice on when to actually inject fuel; other than you should only inject when the intake valve is open. Just how many degrees past the openning seems to be a real mistry and can depend on multiple factors like the type of fuel used, fuel pressure and duration to name just a few. Many of the dumb older ECUs like the one I use (Wolf V550) don't even offer a config for injection timing, just sequencing based on the Ign REF. So you can only move injection by one reference (90degrees for an 8 Cyl). Making sure you swurt into an open valve if very important as emmissions and consumption will be high and power will not be optimum if not. If you have ever had problems getting a good AFR at idle or can't seem to get rid of that rich fuel smell, then take a good look at your injection timing. Map our your camshaft inlet valve against your ECU Ignition reference and TDC to see whether you are injecting fuel when you want to. In my opinion a good starting point is about 20+ degrees after the intake valve opens. From what I can see from the Link ECU setup, they seem to offer 40 degrees as a default starting value. Too far and you may run out of time (the inatake valve closes) if your injection on times are big at WOT.
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The Haltech software allows infinite control over injection timing, and you can map in advance as the engine spins faster (and the window for injection gets smaller). You can also add in more rows and map it to any other input (TPS, MAP, etc). This was preconfigured in my map when I created it and so far, it seems good. Running 1000cc injectors, it idles perfectly at 750rpm. Time will tell once it hits they dyno.

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