HowTo: tune for EGT without a sensor

Td_d · Mar 13, 2012

Firstly - I would like to point out this is not my discovery - hence I am quoting the original poster, an old timer on Romraider.

This is however a very useful technique to keep EGTs safe in tuning open loop - particularly when looking for the effect of leaning out AFRs whilst keeping EGTs safe. I have personally used this for some time, and can confirm that (at least for the GR's) going below 23~24 ohm is looking for trouble - knock city.

Sasha_A80 said:
By checking afr sensor 1 current and afr sensor 1 resistance you may verify whether EGT is safe or not.

ECU tries to heat AF sensor to 750-800C by means of a heater. If EGT is greater the current drops. When current is about zero (0.1-0.2-0.3 amp ) sensor resistance reflects EGT value.

I personnaly ( and first Denso 32 bit ECU as well) consider resistance below 20 Ohm (first Denso AF sensor generation, probably about 25 Ohm for recent) under zero current as EGT extreme. I suppose this is about 850C+, some users report those digits.

From the other hand in case when ECU is not able to reach needed AF sensor temperature and AF resistance is greater than 30 (35 for recent) Ohm you have extremely rich mixture\low EGT that cools down your sensor.

Such a tune with AF sensor resistance of 22-27 Ohm (25-30 for recent ) under WOT is proven safe.

Vermont · Mar 13, 2012

Wow! for me this is like a god send. Come Saturday I want to start tuning my OL on my Gr so this comes at a perfect time. As Holy knows I am rather anal when it comes to knock so I often times pull quite a bit of timing in any area that sees knock. One of the things I was worried about was EGT's getting to high and cooking the valves and also the front O2 (I have heard this is possible with extremely high temps). So for the GR's keeping the resistance between 25-30 ohms when it is as 0 or near to 0 amps is the sweet spot? Now the question I have is if the current never reaches those lower values does that mean you are running too rich? Meaning you still have power to be gained (assuming no knock is present).

Td_d · Mar 13, 2012

Yeah- if you're at resistance levels 35 ohms and aboove, you're very rich, and low egts. You can also see this in the direction that the current is moving.

Vermont · Mar 13, 2012

Td_d said:
Yeah- if you're at resistance levels 35 ohms and aboove, you're very rich, and low egts. You can also see this in the direction that the current is moving.

So not only current but also resistance can be used to measure the EGT's? I thought from that article the only thing the current tells you is if the sensor is "ready to read" so to say. so know when it is heated up.

Td_d · Mar 14, 2012

Yes - but, if you're seeing the current being pulled strongly (i.e. negative -1.5 up) you know that the temps are rising rapidly. It will get to roughly 0 quite quickly though.

HowTo: tune for EGT without a sensor

Td_d

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Vermont

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Td_d

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Vermont

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Td_d

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