What this sensor for
 

I was looking at my exhaust today and noticed a sensor in he cat well it's just after the cat and i can't decide what it is.

It looks to small to be an lambda sensor if i had to guess i would say it was a temp sensor but i'm not sure.

Any ideas anyone

what age car is it mate?

thats a good question.

Car is a my97 imported sti

if memory serves me correct you've got 2 lambda sensors and they are smaller than whats on the earlier 1's with only 1 up before the cat with 3/4 wires

I didn't think cars of this age used closed loop systems.

This will cause problems fitting a de cat pipe

not if you get it remapped,its always wise to have it done after decat as the sensors struggle with the increase in exhaust flow.

correct me if i'm wrong but i was under the impression the 97-98 cars couldn't be remaped

If it's after the CAT, it can only be an EGT or CAT-on-fire sensor, so your first guess was right Dave.

Since their sole purpose is to make sure the Cat doesn't overheat, yours will be completely redundant if and when you fit a decat pipe.

get a daughter board installed and you can then,i tryed puttting afew mods on myn[my96] like decat and induction afew years back and wasnt impressed with the results until i got the remap,and u can damage the engine with det

i like that kind of talk. I'm only de catting it as the cat is blowing so it will have to come off to be replaced or repaired so i tought feck it fit a de cat pipe but i didn't want to start having to remap and the like

well if its leaking then go for it mate but i would be thinking about a remap sometime in the future,youd be suprised by the results.

can you shed any light on the can the 97 ecu be remapped or not

97 ECU can't be remapped, you either need a complete new ECU (Simtek or similar), or I think ESL have just brought out a daughter-board for that model-year, that slots into the standard ECU.

esl daughter is right fella,as stated before.:thumb:

ESL board is not released yet afaik.

But remap or not, not having this sensor that goes after the cat isn't going to be a problem

as above

Your ecu CANNOT be remapped. Buy a simtek and be done with it. No mafs required after that.

ive told him to pm simon he'll sort him out;)

why cant that model of subarus ecu be mapped ? is it locked or what ?

It's really just a historical quirk. Relatively few cars of any make before the late 90s had reprogrammable ECUs, but partly because of the rally connection 93-96 Imprezas had a mounting point for a spare chip on the main ECU motherboard, that meant you could either plug in a new ROM chip or an upgrade board. From '99 onwards virtually all cars started using the OBD2-standard for their ECUs, Imprezas included, which meant you could reprogram them using any OBD2-compatible software. The 97-98 cars have the bad luck of being stuck in the middle of the two eras, with neither option.

thankyou mate for that imfo,allways wondered why and i now know,lol.

That's a good attempt but not quite accurate. The reason why these ECUs are reprogrammable is naff all to do with OBD2, that's a total side issue - and one that arises from the need to develop a standardised, manufacturer-independent, low cost method to allow any garage to check and fix the basic functions of any modern, highly electronic cars, without needing a separate set of expensive diagnostic kit for any brand (or model) they might work on.

Indeed the MY99-00 ECUs are not OBD(2) compatible, which shoots a rather major hole in your explanation.

Even for the newer cars that do OBD2, you can't use "any compatible" software to reprogram them, you will need something specific. Different manufacturers use completely different processor families - and completely different (and proprietary) programming routines to do the job. MY99-00 and newage Imprezas use a totally different programming protocol, for example.

The real reason why newer cars can be remapped relatively easily (and older ones couldn't) is the introduction and then increasingly widespread use of field-reprogrammable flash memory-based microcontrollers in their ECUs. An offshoot of the same technology that brought us iPods and USB pen drives, in other words.

As you say, earlier electronic fuel injection systems used either hardwired, unalterable control logic, socket-mounted ROM chips that needed to be removed to be rewritten, or, as with earlier Imprezas, the ability to run an option/removable map set.

Using a flash-based controller, once they became cheap enough, makes sense for a major motor manufacturer, because it reduces manufacturing costs and also allows issues to be fixed easily by your dealer network without costly hardware changes.