Hi folks, I've just rebuilt my Evo 8 MR engine and popped it back under the hood. Whilst I was underneath and about to re-couple the exhaust back up I noticed that there was no lambda sensor rear of the cat!? I'm guessing that there should be one there and I'm now wondering how the hell it passed the MOT. According to the downloadable PDF manual for my car there is supposed to be a rear lambda sensor and this is what sparked my decision to take a look. The car hasn't had one now for over 3 years and although it passed the first years MOT it has failed the last two, and it's only because I know the guy that he let it go

Thank you.

 

if your car has been tuned maybe the tuner has disable the rear O2.

 

The car is stock, there are no mods on it apart what seems to be a large tail pipe with a 4inch bore.
Cams, fuel injectors are all stock. Are there any gains made by disabling the rear O2 sensor?

 

no there isn't is the check engine CELL is on?

 

No, but it's been a pain to start for months now. Until the piston cracked it just got worse and worse over time, I put it down to a piston cracking and/or a bad coil pack, again, they're all stock, which really confuses me :/

 

The only reason I ask is whether they actually come with 2 O2 sensors as standard and if so I am going to put the rear one back on.

 

Depending on the country and year the emission equipment will vary but I'd guess the reason the rear O2 sensor is missing is the cat back exhaust.

 

So the large bore pipe at the back is called 'cat back'? My car is a 2003 MR and I'm not too clued in on O2 sensors yet, I'm old and never worked on one of these modern marvels - until now that is. I was reading that the ECU needs info from both sensors in order to keep the amount of fuel injected at an optimum, so to my reckoning having only one O2 sensor at the front, doesn't get the exact amount of fuel injected, or am I way off the mark here? I was wondering as to why the emissions failed for 2 consecutive years and I'm thinking that it is because there is no rear O2 sensor.

 

Steve

Heres a pic of a US type EVO CAT w/the sensor port

If your EVO spec has a CAT like this & the port is blocked off then maybe you are missing the sensor. If your CAT has no port, likely it was not required

Also, the sensor wires come out of a grommeted hole in the subpan. You would be able to see that

Also, if we cant figure this out here, the MLR forum is the place to go. Link in my signature (best EVO build)

Cheers, Joe (BTW, youve gotta love that thread title)

 

The front O2 sensor monitors mixture and is used by the ECU to adjust mixture. The rear O2 sensor only monitors converter health (read emissions). If missing It should set a CEL but has no effect on engine operation. My USDM car has the rear O2 port located in the exhaust pipe a good foot behind the converter. Also, I know a good many cat back exhausts don't have an O2 sensor bung.

But since MinusPrevious posted a photograph of a converter with an O2 sensor port right in the middle we see they weren't all that way. I drive USDM Evo 8.

 

My CAT looks identical to the picture. USDM EVO9

 

With the car being over 12yrs old I'm guessing that the original cat has gone as this one seems a little clean to be that old, it could still be the original I guess. The exhaust is definitely not stainless as there is rust all the way to the back box, so this cannot be the original as it would have rusted and gone by now, apparently the original back box (according to the manual) has the exhaust pipe coming into it from the side, mine is just straight through as normal. This is why I was a little confused as to whether it should have a sensor, with it not being the original and being an import (UK) it just seemed as though there should have been one, our emmision laws are pretty strict here. Many thanks for your post and I'm glad you liked the title

 

Do you know whether an import to the UK would have a sensor or not? If I gave the dealership a ring and asked them about it, do you think that they might have the details. I've already bought a balance wheel ring and spacer from them based on me having to give them my reg number/chassis number, would they have the appropriate details specifically from my car?

 

Its a bit tough for us in the U.S. to assist w/this emission type issue on a right hand driver. Yes, call you local dealer w/the VIN & they should be able to pull up the exhaust schematics

Based on your description, the exhaust has been modified to some extent & you do have a CAT in place.
Do you belong to the Lancer Registry forum, because most of those guys are from the UK

When I pull up the schematics on a right hand driver it shows 2 different CATs. 1 w/a sensor & 1 w/out a sensor

 

From looking at the MOT testing procedures, it says they insert a gas analyser into the exhaust stream looking for HC and CO. Somebody correct me if I am wrong, but from what I gather, from the ratio of these two gases they construct a calculated value called lambda, in essence the same thing the front O2 sensor is doing, but they ignore the O2 sensors completely. The lambda value indicates whether the engine is getting the correct mixture or not.

They also say if an engine is running lean it still passes. They don't care if you wreck your turbocharged engine.

You bought a car, it passed the test. Some place along the line it broke a piston probably dumping much oil into the cat. Maybe the cat is dead.

Anyway, I have to admire what the British are doing. On modern cars there's maybe several hundred criteria that can set a CEL. So, ignore all of that and just check if the engine exhaust is clean or not. Why flunk a car because a shift solenoid in the transmission is a little lazy.