Tad266

Good day

So after nearly 1 year i got my rebuild done, car runing done test and failed only emissions on CO its a 98 v4 sti sometimes when she heats up revs slightly jump between 1k to 1.5k but not all times not sure would that be the problem, lambda? one of mechanics says its catalytic converter? any suggestions? have fail sheet pictured there with differences in CO if needed, any help would be appreciated.

Kind Regards

Tad

Kaeo

iTrader: (1)

Can be a dying cat, can be lambdas on the way out, can be a mapping issue too. So many possibilities.

David__H

Or a dodgy MAF.

Tad266

Another fella confirmed 100 % its the cat

BrownPantsRacing

iTrader: (6)

Start by changing the pre-turbo lambda sensor in the headers. If that doesn't sort it then it could be a dying cat.

Tad266

I dont think i have one pre turbo just 1 passed it and one after the cat

BrownPantsRacing

iTrader: (6)

If not then it's more than likely the pre-cat one that's failed.

Tad266

Can it be inspected visually the lambda? Or tested someway when its out?

BrownPantsRacing

iTrader: (6)

Nope. Looking at it won't tell you anything and testing it will cost more than a new one! They are sub £100 so personally I'd just get a new one.

madscoob

iTrader: (3)

you can test a 02 sensor,
easy way is to remove clamp in a vice earth sensor to vice
find the signal wire plug in voltage testor set on 0-1v
then heat up sensor with a blowtorch if you dont see the voltage move up n down when applying heat then it aint working. remember they have to cherry red before they start to work

Tad266

So pulled the sensor out today the one past the turbo it was fairly black cleaned up the insides not that will make any difference or anything but noticed that the actual sensor is fairly new looking and unbranded no signwriting or marking or anything on it so i assume its not genuine? Genuine would be something like denso or ?? correct me if im wrong , also from the sensor into the connector theres 4 wires goin in to it when i only have 3 pins/wires in the female end? Ill defo have to test its not that hard as madscoob says, i hope! thanks guys, more ideas would be helpful its a start i only have the car for over a year dont know all ins/out's on it yet.

RAGGY DOO

iTrader: (1)

50 euro in the ashtray - passed

BrownPantsRacing

iTrader: (6)

Testing as suggested won't test the scaling of a sensor. It's not a switch it's a linear sensor. It will indicate working in some form but won't tell you if it's working correctly.

Also, the post cat sensor won't be at fault for emissions fail. Will be the pre cat sensor.

They are so cheap new surely it's best just to bolt a new one or known working one it?

David__H

I've used Bosch Lambda sensors before, purchased off Lambdasensor.com. Perfectly good.

I agree with brownpantsracing. You can't test the sensor well enough. I'd just change it. The only issue is getting the old one out. Can be a bitch to access and have a habit of welding themselves into the exhaust.

BrownPantsRacing

iTrader: (6)

Subaru were 100% sure the sports cat on my hawkeye was shot. No matter how much I told them to change the pre cat lambda sensor they wouldn't, it kept failing the MOT and wouldn't pass. They eventually gave in to my moaning and changed the sensor. Not only did it pass first time it flew through. They asked me if I wanted a job! Lol.

They did charge me £180 in labour for all if their failed attempts. Very nice of them I thought.

David__H

Oh, don't worry about the 4 wires versus 3 connections.

madscoob

iTrader: (3)

just watch this it prover if its working or not, a knackered one will stay on the same voltage no matter how hot you get it, its worked for me 3 times in 10 years of ownership
any reading under 0.3 volts is shagged

Tad266

I took the sensor out in minutes maybe because its fresh? i was suprised myself i know some of them are a real pain.. ill price one tomorrow in subaru, ebay is around 100 euro shipped, ill check lambdasensor.com dont really like bosch dough before going to order id still like to check the sensor also

BrownPantsRacing

iTrader: (6)

Did you take the pre-cat sensor out or the post-cat sensor? It will most certainly be the 1st sensor in the system, the pre-cat one that will have failed if any.


Also, as said above try to get a genuine Denso one that was meant for the car. They tend to last longer.


The test above will tell you if the sensor is dead, or working in some form, but won't confirm if the sensor is failing, non-linear or incorrectly scaled due to a fault.

Tad266

I took the precat one out yes, i well defo go for genuine no other there is no really point of checking the old one as its a cheap copy and its possibly knackered already, ill post how i get on. Thnx for help every1!

Tad266

So replaced the precat sensor few days ago, went to check emmisions and it is still not good, the CO did change alot in high rev's tough its about right, when idling its still way to high so the mechanic suggested to try cleanout maf also airflow meter and see what happens if not then its the cat more than likely needs to be replaced :/

David__H

Yeah, it was the MAF with my car. When they checked it, it was reading 40 degrees OAT, when it was actually about 20 degrees. Put a new MAF in and it went straight through the emissions test (after 3 previous attempts). When a new OEM MAF I immediately noticed how cleanly the car pulled. So smooth.

Tad266

Sorry i ment to say map thingy not maf kinda in limbo i am here dont know what to do next ill try cleaning them up see what happens

Tad266

Changed cat now also, still CO not right by a g-hair really retest on sunday ill try a bit of dipetane before the test and get it red hot see what happens.

David__H

I had my engine Terracleaned. Didn't help, but then again mine was rebuilt only 15000 miles ago so probably didn't have too many deposits built up inside.

Tad266

Passed the test dipetane done the job, happy days

BrownPantsRacing

iTrader: (6)

Phew! Well done.

Swiss tone

Whats 'dipetane'? some sort of fuel additive? Interested to know in case mine fails!