HowTo: tune for EGT without a sensor

Sasha_A80 · **Posted:** Thu Feb 23, 2012 12:18 am

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.

throttlehappy · **Posted:** Thu Feb 23, 2012 12:36 am

Sasha_A80 wrote:

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 current. 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.

I was not sure about the actual final values, I was logging 'trends' out of normal range on either side but seems I have been in the safe range

Thanks for confirming

ride5000 · **Joined:** Thu Aug 03, 2006 10:40 am **Posts:** 1934

neat trick sasha. good thinking!

mrf582 · **Posted:** Mon Feb 27, 2012 5:18 pm

Interesting. Never thought about this.

Sasha_A80 · **Posted:** Thu Mar 15, 2012 2:13 pm

First generation Denso AF sensor resistance vs EGT ( under low to zero heater current )

25-24 Ohm	23-22 Ohm	20-19 Ohm
810-830°C	830-840°C	850-860°C

EGT sensor 22629AA012, pre-turbo installed.

FrSTi · **Posted:** Thu Mar 15, 2012 3:14 pm

mrf582 wrote:

Interesting. Never thought about this.

Very interesting ! Never thought about this either...
Thanks for sharing.

hellyhans · **Joined:** Thu Oct 18, 2012 2:39 pm **Posts:** 5

Can someone explain this to me please?

Does this mean it's better keeping the EGT sensor in place in the up pipe or if you delete it, it might screw up the AF ratio settings?

I thought all the EGT sensor did was, when it reached a certain temp. It would just give you a check engine light to warn you that gasses are hot and might destroy the Catalytic conv.

GanjaMan · **Posted:** Thu Oct 25, 2012 9:35 am

It would be very nice to make CEL flash light on event of resistanse drops below setpoint value.

Sasha_A80 · **Posted:** Thu Oct 25, 2012 9:57 am

The first 32 bit JDM Denso ecu cuts IAM to 0 if AFsensorResistance<20 Ohm and RPM>4000.
If I am not mistaken I have seen the same for more recent ecu's AFsensorResistance<25 Ohm and RPM>4000.
The difference is due to the first and the second AF sensor generation.

throttlehappy · **Posted:** Thu Oct 25, 2012 6:25 pm

GanjaMan wrote:

It would be very nice to make CEL flash light on event of resistanse drops below setpoint value.

Issue is that resistance drops to below 20 during throttle lift off decelaration before inj cut off

dux10 · **Joined:** Tue Jun 05, 2012 3:37 pm **Posts:** 81

Sasha_A80 wrote:

The first 32 bit JDM Denso ecu cuts IAM to 0 if AFsensorResistance<20 Ohm and RPM>4000.
If I am not mistaken I have seen the same for more recent ecu's AFsensorResistance<25 Ohm and RPM>4000.
The difference is due to the first and the second AF sensor generation.

well that's not the brightest idea: less timing = higher EGT's....
I've noticed as little as one degree can make the world of difference in EGT's...

Steve @ Pullz-On Tuning

fastblueufo · **Posted:** Mon Jun 17, 2013 8:36 am

dux10 wrote:

well that's not the brightest idea: less timing = higher EGT's....
I've noticed as little as one degree can make the world of difference in EGT's...

Steve @ Pullz-On Tuning

I think you missed sasha's point. He is describing that the factory was also using this method as a way of inducing knock control. If the ecu dropped iam to zero because ohm dropped below said threshold at said rpm. Who cares that egt will shoot up if timing is lowered by iam? At that point and from that cause of egt to shoot up its a moot point. The bigger issue would be if the ecu was calibrated to have enough control to drop timing enough to deter det. In some cells on stock timing advance the ecu is only allowed to drop 4* with an iam of zero.

Sasha_A80 · **Posted:** Tue Jun 18, 2013 5:22 am

dux10 wrote:

Sasha_A80 wrote:

The first 32 bit JDM Denso ecu cuts IAM to 0 if AFsensorResistance<20 Ohm and RPM>4000.
If I am not mistaken I have seen the same for more recent ecu's AFsensorResistance<25 Ohm and RPM>4000.
The difference is due to the first and the second AF sensor generation.

well that's not the brightest idea: less timing = higher EGT's....
I've noticed as little as one degree can make the world of difference in EGT's...

Steve @ Pullz-On Tuning

It is not the best idea to just drop ignition timing.
There is a failsafe fuel map that is used at low IAM and may enrich the mixture to make EGT lower. Usually such an enrichment is not sufficient at the stock maps.
Boost control is deactivated under low IAM condition this is good provided wastegate spring is not "tuned".

crazymoet · **Posted:** Tue Jun 18, 2013 10:35 pm

Let us not get too off topic. Remember this is about using the stock o2 sensor as a EGT reference. I am sure there are many other topics relating to timing and EGT.

redwagon · **Posted:** Fri Jul 19, 2013 3:42 am

Has anyone done any testing on late model (BR9 & BM9) LGTs to see how the O2 sensor resistance matches EGT? Since on these cars the front O2 sensor is actually fitted after the turbo...

RomRaider

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HowTo: tune for EGT without a sensor

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