emissions

[maxrs4]

i just failed the mot on emissions!

it failed the lambda and co2 readings, now i have been trying to find my excessive fuel use issue and i'm guessing lambdas would be it!! anyway of checking if i need both or just one? wheres best to get em from? if i do the lambdas will the co2 drop to ok or has it shagged the cats?

[Contigo]

Max where you based? Bournemouth? If you spin up to Newbury I will run a scan on your motor and tell you which Lambda's are out.

[neckarsulm]

Max,

If the lambdas are faulty you will get high Co readings so your catalysts could be OK.
If the lambda reading on the testing machine is OK but Co is high then thats usually a catalyst fault.
You can measure the effectiveness of the catalyst using VAG COM as it compares the readings from the pre and post cat lambda sensors but I suspect they are are fine.

[maxrs4]

Max where you based? Bournemouth? If you spin up to Newbury I will run a scan on your motor and tell you which Lambda's are out.

thanks very much for the offer but i darent drive to newbury with no mot, if you could tell me what to check i can get my mates diagnostics tool!!

Max,

If the lambdas are faulty you will get high Co readings so your catalysts could be OK.
If the lambda reading on the testing machine is OK but Co is high then thats usually a catalyst fault.
You can measure the effectiveness of the catalyst using VAG COM as it compares the readings from the pre and post cat lambda sensors but I suspect they are are fine.

ok lets hope!! thanks for the reply!
i have skyhigh co2- something like 1.9- 2.1 where it should be less than .3
my lambda was lower than the tolerance your allowed!

i also have gutted precats so rely on the main cats to do there thing!

[neckarsulm]

Lower lambda = running rich = high Co2

Sometimes an apparent lambda sensor problem is not really a faulty sensor. An air leak in the intake or exhaust manifold or even a fouled spark plug, for example, will cause the lambda sensor to give a false lean indication as is the case with yours. The sensor reacts only to the presence or absence of oxygen in the exhaust. It has no way of knowing where the extra oxygen came from.
Could be an iffy maf too.

Hence the importance of diagnostics which will allow a scientific decision to be made as what to replace.

[Contigo]

Max where you based? Bournemouth? If you spin up to Newbury I will run a scan on your motor and tell you which Lambda's are out.

thanks very much for the offer but i darent drive to newbury with no mot, if you could tell me what to check i can get my mates diagnostics tool!!

Max,

If the lambdas are faulty you will get high Co readings so your catalysts could be OK.
If the lambda reading on the testing machine is OK but Co is high then thats usually a catalyst fault.
You can measure the effectiveness of the catalyst using VAG COM as it compares the readings from the pre and post cat lambda sensors but I suspect they are are fine.

ok lets hope!! thanks for the reply!
i have skyhigh co2- something like 1.9- 2.1 where it should be less than .3
my lambda was lower than the tolerance your allowed!

i also have gutted precats so rely on the main cats to do there thing!

Well the first and obvious thing to log is the engine fault codes and see if there are any codes related to Lambda sensors and which Bank and side they are on. I think that is the starting step and then we can try logging more measuring blocks to see what the CO2 readings are.

[Contigo]

Oh and next time don't leave it until the MOT expires to get it done! I do mine a month ahead of the expiry so I have time to drive it and recify the problem, should it fail

[maxrs4]

Oh and next time don't leave it until the MOT expires to get it done! I do mine a month ahead of the expiry so I have time to drive it and recify the problem, should it fail

i had been asking questions about my fueling for 6 weeks!!! lol i had suggested it might be lambdas and got sent down the its running cold route as i found out yesterday my gauge doesn't work or the connections don't work properly thus why i know i can change the thermostat without removing the cambelt!!

i have no codes on the system at all! i have checked a few times! i had my car looked over my a mot chap last week and all was well- he didn't check emissions!!

i have receipts for egt sensor but not maf or lambdas, its done 120k so its a toss up where to aim really, ever since i have had it its used lots of fuel and been getting worse, when i first got it i rolling roaded it and got 398bhp and it was rich as assholes! i serviced it and found a filthy air filter and all 6 plugs loose so put it down to that and never had a chance to re road it but it felt noticeably better! i was told it was running 450 odd when i got it and have a certificate to say it did a 3.7 0-60 so 450 would have been about right! im quite up on cars but don't know much on the rs4 having always had vauxhalls in the past!

so if i get my mates diagnostic tool what readings am i looking for and when( eg driving or tick over etc)

thanks

[Contigo]

Got to be the MAF then really if you've done thermostat and there are no codes. You need to measure group 003 to check your MAF peak values.

http://www.ross-tech.com/vag-com/tour/m-blocks.html