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Discussion Starter #1
I was just wondering if someone could answer this for me please.

When people do the 2.2K resistor mod for their uppipes, it puts resistance so the output voltage to the ecu constantly reads 1250 degrees...

Now does the ecu use EGT in determination of its a/f mixtures and its timing for various driving conditions?

I am just wondering, all of these people that are doing this resistor mod, you are all fooling your ecu into thinking that you are idelly running a pretty close to stoich mixture

Since the leads from the probe are cut off, if your engine for some reason starts running lean, you're not going to know... and the ecu is not going to know... so you're just going to blow up.... right?

Could someone please clear this up for me?
Thank you.
 

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The ECU does not use the EGT readings for fueling in any form. All closed loop fueling changes are made from other sensors such as the front and rear O2 sensors and of course the MAF sensor.

The ECU adjusts idle fueling based on the O2 sensors.
 

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Discussion Starter #3
mick_the_ginge said:
The ECU does not use the EGT readings for fueling in any form. All closed loop fueling changes are made from other sensors such as the front and rear O2 sensors and of course the MAF sensor.
what is the purpose of the EGT sensor in the car then? Because it throws MIL's when unplugged or when there is no cat

mick_the_ginge said:
The ECU adjusts idle fueling based on the O2 sensors.
in this case, when people put the pony express mil eliminator on their car, since the o2 sensor value is used in the a/f calculations, but with the eliminator on the ecu its getting an "untrue" value... wont the car be recieving an incorrect amount of fuel now??

also, say someone had the mil eliminator on their car... and the 2.2K resistor mod for the EGT....

say the car gets into a dangerously lean situation, how would the ecu know?
 

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Discussion Starter #4
thank you both of you, i appreciate the replys... as you see i just joined the board yesterday.. lol

i've searched for hours last night, and found answers to all my questions except the two i just asked.

i figured there is some sort of logical answer that im just not aware of, because almost everyone has one if not both of these ecu fixes on their car, but nobodys complaining about exploding motors.

i'll just be working on a car pretty soon, and we will be doing both the resistor and the mil eliminator mod, and it worried me.... because it seemed like we are removing 2 out of the 3 sources for an engine to spot a lean running situation

and its not my car sooo.... once everyone is sure and there is no objection to the mil eliminator and the resistor mod.... and we are sure that the ecu was designed to use the front o2 sensor and maf and other inputs (that does NOT include the egt and the rear o2) in its a/f calculations.... then I will be on my way!
 

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pigeon said:
what is the purpose of the EGT sensor in the car then? Because it throws MIL's when unplugged or when there is no cat

in this case, when people put the pony express mil eliminator on their car, since the o2 sensor value is used in the a/f calculations, but with the eliminator on the ecu its getting an "untrue" value... wont the car be recieving an incorrect amount of fuel now??

also, say someone had the mil eliminator on their car... and the 2.2K resistor mod for the EGT....

say the car gets into a dangerously lean situation, how would the ecu know?
The ECU uses the O2 sensors to work out if it is lean, not the EGT. If you run lean you will throw a code. The only thing the EGT sonsors triggers is panic mode if it detects high exhaust temps which could be just because you have removed a cat.

The Pony Express MIL is connected to the REAR O2 sensor which is only used to do minor fuel adjustments and check emissions. It also only slows the signals down. All fuel tuning is done based off the front O2 sensor.
 

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Discussion Starter #6
mick_the_ginge said:
It also only slows the signals down. All fuel tuning is done based off the front O2 sensor.
so theoretically, if its just "slowing" down the rear o2 voltage... you're really NOT lying to the ecu that much

you are actually giving it a value similar to that of which it would have if a cat WAS still in there... right?
 

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pigeon said:
so theoretically, if its just "slowing" down the rear o2 voltage... you're really NOT lying to the ecu that much

you are actually giving it a value similar to that of which it would have if a cat WAS still in there... right?

When you put in the pony express MIL eliminator you're just giving it a value that it accepts as OK to prevent a CEL. The rear o2 is there to sense if the Cats are working properly, by measuring oxygen levels in the exhaust gas after it has passed through a couple Cats.

The rear o2 is there for purely diagnostic purposes. Technically a wideband o2 could be used by an intelligent ECU to adjust fueling in realtime like a (human) tuner does, but the sensor in the WRX is not used for this purpose.
 
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