Exhaust help please guys

NMcoup22

Hope you guys have got your thinking hats on today.

About 1month ago I had a sports cat fitted, it wasn't one specifically designed for my car it was a universal fit so it had to be welded on.
While the garage was doing that I got them to remove the pre-cat.

Got to admit the car felt great for about 2 day's, then the probelms started.

The engine management light came on, so whenever I had the chance I booked it into my local extortionist (vauxhall dealer),
They tech 2'd it and told me It was either the 02 sensor or the ECU.
Well I've been building computers for over 10 years so I knew their was nothing wrong with that, so I got the sensor changed.

A day later the light came back on, so I decided to find out what exactly the tech 2 said.
I took to friend's garage and when he tech 2'd it the fault code read
02 sensor or catalytic convertor below emissions threshold.

this problem is making me pull my hair out because my m8 did an emmisions test and it passed with flying colours.

what I can tell you is that the universal cat is 300 cells, and the exhaust sytem is a complete weld job by a local custom exhaust fitter.

You guys got any idea what it could be, need advice before I go and spend a lot of cash on complete exhaust from downpipe to backbox.

Cheers. 🙁

vocky

there's two lambda sensors, the one behind the cat (cat is working sensor) is showing the error, but it could be caused by the upper sensor (mixture control)

see which sensor has been replaced and then change the other

the lambda sensors tend to die when the downpipe is removed 🙁

Andy_Coupe

I was in the same boat the other week, took the down pipe off to remove the pre cat, straight after in ran like a bag of shite! Double checked every thing to make sure the sensors were tight and fitted a new manifold to down pipe gasket....... but still had problems, on idle it was very rough and was firing on 3 cylinders, also had the same problem in the low revs after slowing the car down then excelerating. Eventally i got fed up and took it a vxl stealer, they tech 2ed it and after 2 hours they said i have multiply fault codes, first one was that the EGR valve was faulty and the other was that the ECU was broke :shock: . I asked them which was causing the misfire, he said it could be ether :? However i am slightly tech minded and did have a litle understanding what the EGR actually did so i got them to fit one. They re tested it, the EGR falt was cured but they said the ECU is broke and will need replacing. Anyway i drove off with the broke ECU, for 2 days the problem carried on but since then its been 100% problem free, even on the 350 mile round trip to Trax on sunday.
My understanding is that the ecu was picking up the fault on the old EGR valve so when they fitted the new one the ecu still thought it was broke as it had stored the fault code, most ecu`s take around 40-50 miles of driving to sort them selves out so this must have been what happened to mine! Also ive never had the engine management light on so how can the ecu be broke!
How many miles have you done with the new sensor fitted! Also try reseting your ECU by leaving the battery disconected for an hour. If you do try this turn your ignition on then turn it off and within 15 secons you must quickly disconnect the battery or the alrm will go off!

iceberg316

if u drive 30 miles slow and eazy it clears 8)

JohnnyN

Is the weld around the cat joint perfectly air tight??

My weld was broken and it kept drawing in air and setting off the ecu light. When it was Tech 2 it came back that the sensor was too lean. This turned out to be the air being drawn in mixing up the gases.

what..