Stock EGT sensor...same as aftermarket???

[subieworx]

Edit: I should also mention that this is for a Psi3 unit I will be using.

POsted this on nasioc as well, but thought you guys may have more input for me.

I haven't been able to find an answer to this questions and need to know soon as I am changing my gauges out to a new unit.

Currently I have an EGT tapped in the manifold for #4. The unit I am getting will read EGT, but only from the ECU at this point. I have removed a ton of UP's before and obviously know there is an EGT sensor there that the ECU uses, but do not know if it is the same as my aftermarket sensor. My aftermarket sensor is a standard two wire k type sensor. I know the stock sensor is also a two wire sensor, but do not know if it is the same type (I assume it is).

I already have the EGT from the UP removed and have a resistor in the plug. I am wondering if I can take the two wires from my aftermarket sensor and splice them into the stock plug to allow the ECU to read EGT from my manifold instead of UP? I also know that the ECU will be unhappy when EGT's get too high when read on the Up sensor, but do not know what that limit is. I am concerned with this limit as I know the readings will be a bit higher with the sensor being int he manifold instead of in the Up although I have seen that the difference is not extreme.

Any help would be appreicated.

Tony

This is a response I got from Gethin:
The stock EGT is a thermistor and only used by the ECU to detect that the uppipe cat is working, and works more or less like a on/off switch. If the uppipe cat gets too hot then the ECU goes into limp home mode. So you can't use the uppipe EGT as a proper temperature EGT like your aftermarket one, and you can't use the aftermarket one with the stock ECU as it won't work as it's resistance and type is different.

[Jon [in CT]]

Edit: I should also mention that this is for a Psi3 unit I will be using.

POsted this on nasioc as well, but thought you guys may have more input for me.

I haven't been able to find an answer to this questions and need to know soon as I am changing my gauges out to a new unit.

Currently I have an EGT tapped in the manifold for #4. The unit I am getting will read EGT, but only from the ECU at this point. I have removed a ton of UP's before and obviously know there is an EGT sensor there that the ECU uses, but do not know if it is the same as my aftermarket sensor. My aftermarket sensor is a standard two wire k type sensor. I know the stock sensor is also a two wire sensor, but do not know if it is the same type (I assume it is).

I already have the EGT from the UP removed and have a resistor in the plug. I am wondering if I can take the two wires from my aftermarket sensor and splice them into the stock plug to allow the ECU to read EGT from my manifold instead of UP? I also know that the ECU will be unhappy when EGT's get too high when read on the Up sensor, but do not know what that limit is. I am concerned with this limit as I know the readings will be a bit higher with the sensor being int he manifold instead of in the Up although I have seen that the difference is not extreme.

Any help would be appreicated.

Tony

This is a response I got from Gethin:
The stock EGT is a thermistor and only used by the ECU to detect that the uppipe cat is working, and works more or less like a on/off switch. If the uppipe cat gets too hot then the ECU goes into limp home mode. So you can't use the uppipe EGT as a proper temperature EGT like your aftermarket one, and you can't use the aftermarket one with the stock ECU as it won't work as it's resistance and type is different.

Your aftermarket EGT sensor installed near the #4 cylinder exhaust ports is almost certainly a Type K thermocouple, which generates higher voltage as temperature rises. The OEM sensor from your uppipe is a resistive temperature detector, which has lower resistance as temperature rises. You cannot substitute one for the other.

I've always wondered why pilots want to know their Turbine Inlet Temperature, which is essentially what the OEM sensor measures from its location in the uppipe, but Subaru car owners want to know their exhaust port temperature.

[Kha0S]

The common argument for exhaust port temperature is that a specific cylinder running lean will be averaged out by the time the combined exhaust stream reaches a turbine inlet temperature sensor, and a poor tune will not be caught as soon as it should be.

Subaru owners, instead, choose to assume that one specific cylinder will run lean before the rest. While this assumption can be supported by the stock fuel rail design (and, perhaps, is negated when an engine is modified for use in aircraft by possibly changing the fuel rails), it's still not a guarantee.

/Andrew

[subieworx]

Exactly, which is why I want to be able to use my aftermarket probe located near the head, but have it read through the ECU instead of a separate gauge.

THis is more about the possibly of doing that, than where to mount an EGT gauge. I figured you guys would be a good source as you knowthe ins and outs of the subaru ecu and could tell me if that was a possible combination.

[Kha0S]

THis is more about the possibly of doing that, than where to mount an EGT gauge. I figured you guys would be a good source as you knowthe ins and outs of the subaru ecu and could tell me if that was a possible combination.

It's potentially possible with some complex driver circuitry, but not feasible, and would result in the car throwing codes and limping (due to the higher temperature seen at the port vs. farther downstream).

[subieworx]

Well crap. I really don't want to keep a gauge around after getting the psi3 unit, but do not trust the factory egt to give me any kind of usable data.

BTW, thanks for the help guys.

Another question yet to be answered. At what point does the high egt readings send the car into limp mode? I have been thinking about lengthening the wires on the stock probe and installing it in the manifold, but am very afraid of this as it was not designed for that area and seems to be rather fragile. I see a possible ingestion of egt probe by my turbo....

[Jon [in CT]]

Another question yet to be answered. At what point does the high egt readings send the car into limp mode? I have been thinking about lengthening the wires on the stock probe and installing it in the manifold, but am very afraid of this as it was not designed for that area and seems to be rather fragile. I see a possible ingestion of egt probe by my turbo....

You'd want to cut out the EGT sensor bung from an old uppipe because it has a unique (i.e. patented) seat design. You'd be unlikely to encounter a "too hot" trouble code, which is only set when a temperature greater than 1050°C (1922°F) is detected for at least 200 engine revolutions. If those conditions were encountered, you'd probably be happy the ECU turned on the MIL and adopted limp mode.

[subieworx]

Wow, that temp is high. I will (hopefully) not have to worry about hitting that as that would be bad.

Do you see any problems with the probe breaking if I were to locate it in the manifold? The rumors are numerous about people having their UP egt sensors breaking off and getting ingested by the turbo, yet I do not htink I have actually heard of a documented case of this happening.