406oc.co.uk

Hey guys, I have a D8 406 2.0L 16V 135bhp motor. The problem is, the catalytic converter was blocked and went kaput a couple of months back. Took it to the dealer and they removed the cat and patched a 'bullet' box in place of the cat. Re-attached the lambda sensor and everything went well. Weeks after that, the K light started poppin up. Took it back to them and ECU read a fault with O2 sensor. But with further checking, the 02's sensor opertating voltage range seems to be in an acceptable condition and they adviced me against changing the sensor. They just cleared the fault code and I went on my way. The K light still comes on and off intermittently.

On the next routine service, they plugged in the reader to check on the K light fault codes, and this time its showing 'Permanent fault: mixture regulation auto-adaptation - upper stop'
They are also clueless on what to do, and my car seems to be running rich at all times. There's a strong smell of petrol fume coming out of the tailpipe, I guess due to unburt fuel and on cold starts in the morning, the water coming out of the exhaust is black and full of soot. I guess there's a lot of carbon buildup somewhere in the system. Fuel consumption has shot thru the sky lately and I really do not know what's wrong. On kickdown acceleration, a slight hesitation occurs before the engine roars up the rev range smoothly. What could the problem be guys? I'm really out of ideas. I would appreciate the help.

LP640 wrote:they removed the cat and patched a 'bullet' box in place of the cat

Seriously? It won't pass an emissions test like that.

What I'm wondering is if the fuel problem killed the cat or if the fuel problem is caused by the exhaust not having enough back pressure now & putting the fuelling outside the engine management's ability to compensate

steve_earwig wrote:

LP640 wrote:they removed the cat and patched a 'bullet' box in place of the cat

Seriously? It won't pass an emissions test like that.

What I'm wondering is if the fuel problem killed the cat or if the fuel problem is caused by the exhaust not having enough back pressure now & putting the fuelling outside the engine management's ability to compensate

I'm out of the UK actually, emissions test is not a worry here although without the cat, its not very nature friendly. I never had this problem before the cat died. Everything was fine till the cat got stuffed and I hardly got any speed when driving.

What are my options now, refitting a cat or going for a different exhaust setup with more back pressure? I would definitely like to solve this issue, as having the K light popping on is not one of those nice things to look at.

It would fail an emissions test here in Croatia but I've no idea in Malaysia. Stuff the environment, global corporations like Coka Cola screw it up far more comprehensibly than you or I ever could.

I don't really know how much affect on the engine loosing the cat will have, we now need someone to tell us if it will or not so we can then move on to diagnosing the fault.

Is the o2 sensor before or after the cat on this car? If it's after, then it's no wonder it's misbehaving and you should get a new cat fitted

If before, I'd suggest an ECU reset. Unplug the battery for an hour (after making a note of your stereo code, if it's the factory unit) and expect it to run a bit rough for the first 20 miles or so.

mjb wrote:Is the o2 sensor before or after the cat on this car? If it's after, then it's no wonder it's misbehaving and you should get a new cat fitted

If before, I'd suggest an ECU reset. Unplug the battery for an hour (after making a note of your stereo code, if it's the factory unit) and expect it to run a bit rough for the first 20 miles or so.

To be honest, I can't recall where the sensor is located on this car prior to the cat removal. Anyone else could shed some light on this?

But after the cat removed and replaced with a center silencer, the sensor is put back in between the flexi section and the new silencer, if I recall correctly.

I have the ECU reset method, the light goes off for a bit (10mins or so) and it comes back on intermittently soon after. Does this mean I should get a new cat fitted? A replacement cat here cost silly money, and parts for 406s are scarce.