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[juliangungho]

Ok I am new to this foroum as the misses has a 2.6  vectra b  which is used in the omegas obviously . I have been thru this foroum looking up the fault codes  p0420 and p0430  and  followed the advise in moving the post lambdas  to behind the main cat. Ok I did this on the weekend  , I had a spare set of mainfolds ready so I left the original post lambdas in place  and used another set of lambdas (post)  and   fitted them behind the cat. I used "My Naff Code Reader" to check the values  ie the air fuel ratios and  this is what I get.

1. Both pre lambda are flicking between  rich/lean in about 1 sec intervals and from what I have been reading this is correct as is the values  for milli volts, both lamdas are  putting out the same readings.

2.  ok the post lambdas are reading lean  in the air fuel ratio, Am I correct that as the main cat is doing its buisness I should only see lean readings? I rev the car and it stays lean  and does not go to rich. The milli volts is going up and down  the same as each other  so I can assume that parts correct.

Ok I did have one  glitch were the spare lambda went lazy on the air fuel mix so I used another from another spare set of maicats that I had and it was back to normal. So in theory  this should  stop the 0420 0430 codes coming on well last nite a fault code showed again, it was 0420      there was no 0430 but this may have come on eventually but I dont know.

So the light is back on and following the advise in moving the  lambdas back wards to behind the new cat which I would like to point out is now brand new as  the flexi had failed on the original so I had to buy a whole new down pipe. So I am  stuck and the only thing that may have had an influence was the depth of the probe of the lambdas  in the exhaust stream. The actually lambda end is dead flush with the ID on the exhaust,  would this have made a difference, do I need to put the lambdas further into the exhaust flow??

I 4eset it all last nite with "My Naff Code Reader" and will see if the codes come back  , also did I need to reset the lambda feedback loop thats showing in "My Naff Code Reader"???

Thoughts much aprreciated.

[Kevin Wood]

A tough one. There's no real way to check the output of the post-cat lambdas because they depend what the working condition of the cat is. I would expect them to pretty much follow the pre-cat sensors until the cat starts working and then it's anybody's guess. If both sensors are showing activity of some sort (try blipping the throttle and see what happens) I would say they are OK.

The ECU runs a cat check cycle once the engine is up to temperature and driving conditions are right. This consists of setting a constant rich or lean mixture for a few seconds and observing how long the rich / lean indication takes to propagate from the front Lambda sensors back to the post-cat sensors. If the cat is working there will be a good delay as the cat absorbs the excess oxygen or depletes its' stored oxygen depending on the mixture.

The sensor being out of the main airflow will cause it to react a little slower so this would tend to make the cat look more effective. Unless it's now reacting so slowly that the ECU is interpreting that as no activity...?

Might be worth swapping the post-cat sensors between the two banks and see if the fault follows the sensor?

Kevin

[juliangungho]

Ok you mention  the following

"The sensor being out of the main airflow will cause it to react a little slower so this would tend to make the cat look more effective. Unless it's now reacting so slowly that the ECU is interpreting that as no activity...?" 

Thats what I was thinking I even tried the spark plug defoulers and  that  didnt help either.  I am clasping at straws here but may be the lambda tips do need to be  well into the exhaust stream  to work, now that I have the  new cat fitted maybe I should  lower the  tips  further in. This will mean some work me  as I have welded in new boses so I am going to have to grind them down a bit .

I know the post  lambda dont effect the perfect the performance   so whilst they are on  there is only the dash light to have to worry about but dont want to remove it just yet.

A tough one. There's no real way to check the output of the post-cat lambdas because they depend what the working condition of the cat is. I would expect them to pretty much follow the pre-cat sensors until the cat starts working and then it's anybody's guess. If both sensors are showing activity of some sort (try blipping the throttle and see what happens) I would say they are OK.

The ECU runs a cat check cycle once the engine is up to temperature and driving conditions are right. This consists of setting a constant rich or lean mixture for a few seconds and observing how long the rich / lean indication takes to propagate from the front Lambda sensors back to the post-cat sensors. If the cat is working there will be a good delay as the cat absorbs the excess oxygen or depletes its' stored oxygen depending on the mixture.

The sensor being out of the main airflow will cause it to react a little slower so this would tend to make the cat look more effective. Unless it's now reacting so slowly that the ECU is interpreting that as no activity...?

Might be worth swapping the post-cat sensors between the two banks and see if the fault follows the sensor?

Kevin

[juliangungho]

also if the main cat is doing its job when running at optimum temperature should the post lambda   be reading lean  on a permanent basis as the cat wil be doing its job?

[aaronjb]

I haven't watched the outputs on an Omega, but certainly on other cars where I have (mostly the MR2) the post-CAT sensor(s) swings rich/lean, just much more slowly than the pre-CAT sensor(s) - in the case of the MR2 it's that 'delay' the ECU is looking for..

[juliangungho]

the delay I assume being from the cat doing its job thus  if the lambda tip is not fully in the exhaust stream  it would run lean for to long and if the ecu is looking  for the ocasional "rich" then that may be my problem possibly ie the lambda tip  needs to be moved in further - Am I finking along the right lines??

[juliangungho]

I can remember watching the air fuel ratios on saturday  on the post lambdas and they stayed lean even when revving the engine so can "My Naff Code Reader" be used whilst the car is being driven? or does it close the port off when the ecu detects it being driven?

[juliangungho]

Ok I have been out playing tonite with "My Naff Code Reader", the car was stone cold and was not used all day.

Op com shows snabk 1 sensor2 and bank 2 sensor 2 showing  lean even from start up and it stayed like that right up to when the fans kicked and the engine rev now and then. The precats snesors were doing there job  but i  am unsure if the post lambdas are doing theres. I swapeed them back over to the original positions and the readins stayed the same  so lean it stayed.  We did a live recording   for the whole duration and excell shows it via filters that both post cats only showed lean from intial start up to  the fans kicking in and with bliping the throttle now and then.

 Does anyone  have a map they can check to see if theres does the same  ie the post cat lambdas stay lean permanently?  ref a y26se engine

help required

[Brikhead]

What fuel are you using? If it's regular unleaded maybe try switching to super.

[juliangungho]

been running super unleaded and even tried v power for a month  no difference. but I have been reading something tonite.

http://chase.co.nz/AboutChaseOxygenSensors.pdf

page 5 , it mentions that if the  post lamda sensor  has the same readings as the  pre sensor the cat is failing. well the reading in milli volts is the same in both post and pre but the air fuel ratio stays in  lean..   I had the car down the mot station sat morning and the  emissions test was spot on so I doubt i got a dodgy cat its brand spanking new .  I checked the readings on the original manifolds as well and the milli volts is the same so the more I keep reading into this the more iam confused. I cannot get the post sensor to switch  over to a rich condition , but then is it ment to???