And which lambda do you want to change? Pre-cat or after-cat?
Pre-cat has 430mm wire, after-cat 600mm wire.
What prices did you find? Here in czech rep. I can have Bosch 0258006376 about 67 euro, NGK OZA659-EE49 about 53 euro.
You should do the test that i wrote in #38, to be sure what lambda is faulty.

thanks for info DC

hanz i took a look at your post about lambda readings at speed... for starters theres nowhere i get 90MPH legally, and i dont mean this in a nasty way at all but how will this prove or disprove failure of the post cat sensor? as far as im aware these engine shut off the injectors when 'free wheeling' in gear so i would be expecting to see minimal or no compensation from the lambdas (minimal voltage from pre-cat and minimal to no voltage from post-cat).
at the risk of going back over what has already been explained the issue seems to appear when holding constant rev ranges for periods of time (i have cruise control on 95% of my way to and from work as its motorways and im trying to push MPG) the fault always returns at some point when im on cruise control. i have never had it occur when town driving. my limited knowledge of sensors suggests to me that this could be an indication of the sensor not reading properly due to deterioration of the zirconia component/wiring altho i know that HO2S only have a life expectancy of about 100,000mi its done 86,000mi so id be expecting to replace one if not both around this mileage but the OBD is reporting post-cat and catalyst efficiency the cat efficiency is surely sensed by the post-cat sensor compared to fuel dosages and pre-cat sensor...

richydraper: oh sorry, now I see, that I made bad conversion! My graphs are from 80km/h to 120km/h, so this is from 50mph to 75mph. But no problem, to do the test on 4th gear from 35mph to 55mph.
About lambdas - I'm almost sure, that you have faulty pre-cat lambda, because it didnt reach below 0,24V on your log. And didnt reach 0V when breaking. This bad information lead ECU to bad fuel mixture and this cause bad function of cat and post-cat lambda.
You can take a look to this page: http://www.autolabscopediagnostics.com/sensors2.html
The first graph is bad lambda, that reached minimum only CH1min=314mV and after change (the second graph), you can see, that lambda reached 110mV.
The test mentioned above should prove, that lambda do not reach 0V on breaking, which means, that is definetely faulty.

my graph wasnt done whilst driving... i did it whilst stationary in my garage

yes, I know. so the test-drive mentioned above is needed.
... i wrote breaking, i know, but you only release throttle, and injector was closed like when breaking...

got it now... sorry bud crossed wires!

ill hook up a test drive and see what happens

hi again...

had my intermediate pipe off whilst messing around with gear cables recently as i looked up the down pipe from the cat where lambda sensor 2 sits not good...

to my amazement there was hardened deposits of some kind of molten metal dribbling from the cat and covering the 'leading edge' of the sensor it wasnt particularly hard i could bend it with my fingers so its almost like tin or aluminium, it wasnt covered in soot like i would have expected but a dull metalic grey im assuming this isnt going to help anything

due to time constraints i didnt manage to get round to sorting out so its one for another day i knew cats ran hot but to see these deposits has got me thinking that something somewhere isnt too healthy!

That's not good. See if it conducts electricity by checking resistance then maybe it's a silicon compound as silicon is a semi conductor? There was a load of that in fuel around London a while back

there was even more of it in tesco fuel not so long ago after you saying that i guess it could be both lambdas dont look particularly old but saying that none of the engine is that tatty it does certainly resemble almost a 'lava flow' of a metallic substance though

If it's any help, I'd expect really unsteady rpm on tickover if the pre cat lambda was contaminated with silicon. Have a look at the lambda readout and if it's flip flopping nicely at tickover then that's probably ok

now then, now then... fitted a new post cat lambda today as it all signs were pointing that way and cleared the fault codes so as of yet no MIL (altho i have only done 25 miles)

but the deposits in the cat... well heres a pic of what i pulled out of it

and im still standing by my original statement of it seems to be a soft metallic substance but the plot thickens... embedded in said strange substrate is a small piece of cat monolith and the whole lot is coated with what i can only describe as 'rocky' deposits which at a guess is powdered ceramic

...now for the kick in the knackers...

what the actual funk has happened to my precious platinum and rhodium stuffed box of planet saving excellence!!!

did a little bit of google-ing (which IS different to oogling according to the mrs) and from what i can make out it seems to have suffered 'meltdown' which apparently is when abnormally high levels of unburned hydrocarbons reach the monolith. this results in 'significantly increased' heat buidup in the monolith and would seem to tear it apart :bang::shakehead::doh::dead::yuck:

thoughts please

no thoughts...

i was thinking of getting a 'pre mot' emissions test done to see if its effecting it and also thought about knocking the monolith out

*thinks maybe 'discuss' will work*


discuss... @MEP

father in law's car was getting p0420 and when i took the cat's off his car, his kitten (mini cat attached to exhaust manifold) was totally destroyed,

on my golf i had the same code too, so when i climbed under the car had a rattle on it, removed it and it had collapsed,

soooo a pre MOT emissions test showed up .70ish lambda... a pass is .15 so im at least .55% out.

ASSUMING my cat is still functional would running injector cleaner (Redex/X1R/Other) removing the air filter, re-gapping the plugs and resetting fuel trims give me this half a percent that i need to get it through test?

You sound a bit confused there Richy
A UK MOT test lambda pass is as near as possible to 1.0.
Limits are 0.97 to 1.03. But this measurement, taken from the end of the exhaust pipe, is very different from your own car precat lambda output signal which is normally varying between 0.1 to 0.9v at tickover and the post cat lambda which could be anything within that range but won't be 1.0

Fuel trims in themselves are not a worry, it's what your ECU is having to do to make the engine run correctly. It doesn't mean your engine is running rich or lean. More importantly is why the fuel is having to be trimmed so much from the baseline figures. ETS, clogged injector, air leaks, even a mistimed engine can all cause fuel trimming to be required

now you've said that im beginning to see the holes in my previous post...

im gonna go with i misheard 0.5 as .15 and assumed he was on about lambda levels. so if its 0.7% CO then ill be fine with some inj cleaner and good boot round the lanes before test.

if he was on about lambda readings being .7 then im under the threshold for lambda... but what does that actually mean?

one thing i really don't understand is the whole emissions thing because im a diesel tech and i've never had any experience with emissions test gear etc etc.

For the MOT test emissions then they put a sensor up the tailpipe and measure emissions there and a figure close to 1.0 means that the fuel/air mix is good (around 14.7 parts air to 1 part fuel) and it's a pass

The pre cat lambda on your car is looking for the same thing but is constantly swinging and making the car switch from slightly rich to slightly lean so it's always switching around the ideal at a steady rpm

The post cat lambda largely checks on the condition/ efficiency of the cat ie if the post cat trace is the same as the precat trace then the cat logically isn't doing anything and it would flag up a P0420 cat efficiency fault code

The tail pipe check will discover an exhaust leak between the cat and the tail pipe and show up as excess oxygen even though your engine set up may be perfectly good

if he was on about lambda readings being .7 then im under the threshold for lambda... but what does that actually mean?
If your emissions at the tailpipe were 0.7 then your engine wouldn't be running

Hi to you all!

My first post..

My Fiat Stilo 1.6MW 2003 gets same error code P0420, nothing else (no lambda codes etc.) I read it with multiecuscan+ELM327 v1.4.

Here is some data.

Simple question, is my kat gone bad or something else?

First picture is taken warm engine, about 3500-4000rpm.
Second instantly to about 800rpm idle speed.
Third is quite hot engine and idle speed.

Anyone?

give me a couple of days ill have a look at my lambda traces after i get her MOTd tomorrow.