which cat to use ?

[papalion]

hi i have an audi a4 1.8 t sport 2004 cab , and the engine light light has cmoe on i was thinking of replacing the cat , but the listings only show the saloon . my part number is 8e0254200a , but im told the saloon is diferent to the cab , is this correct and if so in what respect ? many thanks .

[VAGMAN54]

dont know the differences but why do you suspect the cat ?

[papalion]

when i read the fault code it comming up as cat system below effiecincy or threshold p0420 o mention of o2 sensers . why is that do you think it my be somthing else ?

[VAGMAN54]

could be a rear lambda fault or if a none gen cat is fitted then it could be that

[papalion]

thanks but i thought if it was an o2 senser would it not throw a different code up ?

[VAGMAN54]

it could be within it limits and maybe is the cat but i have known them be a problem and show your 4020 code even though an ageing check has proved ok....if they are faulty they tend to stick at around .475 volts and dont vary a lot....worth checking thats all im saying

[papalion]

thanks ill look into that cheers .

[wmccann]

Hi,

Part number for the catalyst is 8e0 254 200 AX - x meaning you have to exchange your one.

This is an expensive piece of kit!!

Walter.

[papalion]

thanks for the part number . i have seen aftermarket cats but also read that these wont clear the code . i should have put that the car has 115 k on the clock . And that the collar on the dip stick came away which ment the engine was over filled with oil for a few miles before the oli was checked and level corrected .

[papalion]

ive had my lap top on my car and only getting a reading fron one of the 02 sensers , dose that indicate one of them is at fault ? if so is it the one im getting a value for or the one that is not sending any value ? thanks

[VAGMAN54]

the one with no reading,are you sure there is no reading at all because they normally fail to .475 or half a volt .500

[papalion]

just changed both , the rear one ran the car and it was reading around .700 . then changed the pre cat one and ran the car still no reading but the rear one dropped down to . 500 so now im a bit confussed . thanks.

[VAGMAN54]

you need to check the wiring on the front lambda that is not right,thats why you have a p4020 code your car is running on the rear sensor,when you have found the fault the rear one will drop to nearly 0.00 may be a little higher than that but not a lot,but untill you have found the front problem then you will always get that code

[papalion]

thanks for that il check it out , didnt think it was right as everything is the same as bofore .

[papalion]

one more question , and thanks for your help , do you know the which wires are which ? how do i test them and what do i need to look for ? thanks .

[VAGMAN54]

need year and engine code of your car,i might be able to help with pin numbers at ecu..if you do it on a continuity check everything should be zero between one end and the other at the sensor,check all wires at the sensor and ecu you should only have continuity on the wire you are testing and not on any other from the sensor

[papalion]

thanks its a 2004 bfb engine code . i disconected the plug and ran the car and got p0130 o2 sensor code up . and p0030 heater control circuit up . pluged old sensor in and got fuel system closed loop . pluged new one back in and found a reading on another page saying o2 sensor 1 bank 1 (wr) with a value of 127 mA and -0.03 mA but stil getting readings 0.70 and .45 its all over the shop !!! .

[VAGMAN54]

if you have a label file look in there,but the channels i think you need are 31..32..33 they should tell you your fuel ratio etc etc let me know what they have in them,your lambda is working but by them reading it looks like you have to much oxygen in the exhaust

[papalion]

my reader is not that advanced , which readings are telling me there is too much oxygen ? thanks

[VAGMAN54]

dont know what you have on your machine but your front lambda should have a value of 1.00 which is your fuel air mixture which is what you should be aiming for,anything below is too much air anything above is too much fuel

[papalion]

The car has just come back from its mot and passed the emissions with the results : fast idle C0 0.03% HC 7PPM ¬ 1.020 (NOT SURE WHAT THE LAST ONE IS BUT IT GIVES THE VALUES O.970-1.030) AND ALSO NATURAL IDLE AT 0.02% are these what you would expect to see ? thanks .

[VAGMAN54]

yes ....except the 1.020 is a little high that would be better at 1.000 but isnt far out but a small amount of air is getting in somewhere check your exhaust system for a small hole that would be enough to cause that but your co at 0.03 is bang on certainly no cat fault there ...

[papalion]

thanks for the advice , so you think they could be air being drawn in , starting from the outlet manifold up to the cat or passed the cat ? this .020 what problems is going to cause if i let it run at that ? i take it this is the lambda readings ?

[VAGMAN54]

yeah check the full system,,no damage but if your engine check light is giving you a p0420 code i would be checking the rear lambda