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Purchased downpipes with pre cats removed off eBay and upon fitting the car is running really rough. Can only think that lambda sensors have give up as there is no leaks from joints. Have replaced front lambdas but nothing has changed, I'm awaiting rear sensors to be delivered, the engine light is on but plugging VCDS in doesn't bring any fault codes up? Can anyone help? Cheers

fairly sure you need spaced lambda or stage 2 map to map it out if the pipes are straight pipes? hopefully somebody else with them already fitted can confirm?

They've just got the first cats removed and the big cat is still inside. Link to them is below.
https://www.ebay.co.uk/ulk/itm/272213251843

I had my precats taken out by Mrc. I believe they mapped out a sensor when they did it

Thanks for your replies. I'm hoping that's not the case as I was told that no remap was required.

Remap is not essential although it is recommended. I run spacers and have had no issues.

The secondary sensors only monitor the efficiency of the precats and will only warn you if they fall out of limits via a CEL but shouldn't change the fuelling as that is delt with via the front lambdas as far as I am aware!!!.

I'm guessing the labda sensors have been put into the correct banks?. I remember someone having an issue as they were installed the wrong way round!!!

They were put back in the same holes that they came out of. The 2 front sensors have been changed for new, I plugged laptop in and monitored all sensors and noticed that there isn't voltage going to one of the back sensors while the other has. I pressed clear codes and it seems to be running better with the occasional splutter? I'm confused.

I think you might need to run it for a while for the fuel trims to settle down as clearing codes resets these. Go to block 032 to see your idle and partial trims

Block 32 reads idle -0.8% and partial read -9%. It can drive ok then it's rubbish again. Do then readings look ok?

Bank 1 is showing idle -6.6% and partial -18.0%. Bank 2 is showing idle 0% and partial 17.6%. Somethings not right.

No, somethings not right there.

The negative numbers are pulling fueling to combat a rich system and the positive number are adding fuel to combat a lean system.

I believe the ideal numbers are +\- 5 for idle and +\- 10 for partial. So somethings clearly amiss, bank 1 being too rich and bank to being too lean.

Are you getting any DTC's showing?

I'm quite away from them figures then. only dtc codes are emissions related but that's all I can see unless I need to look somewhere else?

Plugged in laptop today and it says there is a misfire on cylinders 1,2&3. Could this be the problem? Can't understand why it's only just come up with them codes though.

Misfires might be caused by the problem but won't be the problem.

Not sure if you can have the lambda leads in the wrong banks but have you made sure they are in the correct sides? Someone mentioned earlier it could be a problem. Post a full scan up so we can see the codes

I'm pretty sure they went back where they come from. I know connectors were brown and black! What do you want me to put a scan up of? Appreciate your help mate.