EGT Issues after decat
 

Hey,

I recently swapped out the downpipe on my 2003 Blobeye WRX for one with a high-flow cat, also removing the cat pipe and swapping the uppipe for a cat-less STI one. I’m not sure if this is connected.

So I got a new EGT sensor and it is just reading either 200 or 365 (°C), nothing in between and nothing other than those two numbers. I’ve tried a different EGT sensor and I get the same result. Before I changed the cats, it was working fine.

I’d like to keep the sensor as a failsafe - especially as I’m running meth/water injection and want the added backup in case the meth system runs out/fails and I don’t realise.

I have CELs for slow lambda sensor response (due to the cats), and sometimes I get CELs for low EGT voltage. I’ve tried clearing these/resetting ECU and it doesn’t change anything. The EGT sensor is OEM.

Has anyone else had this EGT sensor issue? Or knows what it could be?

Thanks :)

Out of interest where have you fitted this EGT sensor?

It’s at the exit of the manifold, after all the headers have merged, just before the uppipe.

That location would be where the A/F sensor would normally be fitted unless you've changed/modified the manifolds?
https://cimg4.ibsrv.net/gimg/www.sco...d7298d34e5.jpg

Yes, that’s correct. That wouldn’t affect the EGT sensor working though, would it?

Think he's talking about the EGT probe Don. Usually they're just disconnected or coiled up and cable tied somewhere. It should live after all the cats at the end of the downpipe.

Why after the cats? I thought it should be close to the manifold to get the most accurate reading?

Also, that wouldn’t change the fact it’s not reading correctly, would it?

Just to be perfectly clear, you've moved the location of the EGT probe from it's old location at the top of the up-pipe to somewhere close to the O2 (A/F) sensor (Bank 1 Sensor 1) by welding on a boss, drilling and tapping the manifold and extending the wiring to suit?
https://cimg2.ibsrv.net/gimg/www.sco...51fc197958.jpg
Is the tip of the probe in the central gas flow?

How are you reading the EGT output values?

Referencing your CEL's which slow response one did you get?
P0133 O2 (A/F) Sensor Circuit Slow Response (Bank 1 Sensor 1)
P0139 O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)

and EGT low voltage?
P0545 Exhaust Gas Temperature Sensor Circuit Low-Bank 1
P0546 Exhaust Gas Temperature Sensor Circuit High-Bank 1

Hi Don. Thanks for your replies today

That is correct. All apart from extending the wiring. Unclipping the EGT probe plug, from where it sits at the top left of the engine bay, gave enough length for it to reach the probe in its new position.

I have no reason to think the probe tip isn’t in the centre - it sits just as proud from the external of the pipe as it did in the OEM position (and to eye the pipes are the same diameter). Even if it wasn’t in the centre, I would’ve thought the readings would at least fluctuate instead of sitting at one of two discrete values.

I’m using a Tactrix v2 cable, reading through the ECU. I have used this to both log independently to SD and through RomRaider logger.

The CELs were for P0139 and P0545.

Thanks again

Put it back where it's supposed to be then you'll have no problems.

Why would that stop it working entirely though? It’s only a k-type thermocouple. It will output a potential difference relative to the temperature experienced. I don’t understand why it’s only giving 2 discrete output instead of a quasi-continuous output

It almost seems like a short, and I was wondering if anyone had countered this before or could give me further insight

It is probably going outside it's working parameters under certain conditions. The amount of temperature drop after travelling through two cats and a turbo is significant.

Yeah, I can appreciate that. And I’m not writing off re-adjusting the position. I just feel that it should still read something, even if it’s only before the engine is running at full temperature - and it’s a fair bit of work to move it round so wanted to make sure I wasn’t missing anything obvious.

Did you look at the DTC pdf attached to post #8 ?

Sorry, I totally missed that. That looks great! Very much appreciated, I will work my way through it. Thanks