Failed Emissions - High CO on BMW E36 318i

As above,
Also include some injector cleaner and a good squirt of carb cleaner through the AFM and the fix all ITALIAN TUNE UP.

Chuck a litre of mineral 2 stroke oil in the fuel and take it for an Italian tune up before the smoke test, then make sure the tester tests the emissions whilst the car is hot.

Have they failed it on the retest then ? Don't see many older cat cars now but I just put the pedal presser on The throttle at 2800rpm and let it sit for a couple of mins after a few hard revs to get the cat lit . Your hc readings are a little low and co a bit high to get through without a cat treatment , can take a while to come down

a bit curse word, often good for one MOT and thats it.

What the Welshman said .

FWIW I have been there and done that with two cats now. I'd rather get a good secondhand item if you can.

But as said I'd check for the basics like vacuum leaks etc. But if it is running fine then it probably is the cat going by the readings. As a rule of thumb:

CO = How rich the mixture is
HC = How unburnt the mixture is ; I believe an engine burning oil can influence this reading as well
Lambda = how close it is the ideal stoichometric mixture. 1 tends to equal 14.7:1 (parts of air to fuel), the perfect air to fuel mixure. Less tends to indicate the mixture is rich, with higher than one suggesting it is too lean.

But that is a very loose explanation!

What year is it? My friend has a 2000 E46 328i that pre-dates OBD-II. My INPA lead works with a BMW converter lead hooked up to my OBD-II lead, which is a VAG K-Line cable.

On that I've been able to do a few things, including
-Getting live data on various sensors, including the parking sensors (PDC)
-Clear his airbag light quite a few times - this it seems can only be done through the BMW port ; disconnecting the batter will not make the car forget.
-See codes that did not throw an EML. These included ;
-Cooling being outside the set paramters ; it's come close to overheating a few times due to a previous airlock.
-It cannot see an engine fan ; it's long gone and some crappy aftermarket thing is there
-Lambda Sensor Errors on both banks ;
-Misfire on a number of cylinders ; it was running the factory plugs it seems for a very long time.

If you were closer I'd offer to check yours out.

FWIW INPA is the BMW factory scanning tool. It's clunky to use but it can be very very handy.

Thats not a cat, it looks like a pre muffler / absorption chamber. Basically a small box with a straight through perforated tube with glass wool around it.

Doesnt it have a cat further forward? Possibly in the manifold.

INPA should work on XP but it can be a royal pain to setup. I did cheat. By this I mean buy a cable and the software off a bloke who presets all of the software up .

Anyway.

Your exhaust should look like this if RealOEM is correct:

www.realoem.com/bmw/enUS/showparts?id=CE32-EUR-04-1999-E36-BMW-318i&diagId=18_0227

www.realoem.com/bmw/enUS/showparts?id=CE32-EUR-04-1999-E36-BMW-318i&diagId=18_0230

The exhaust having two 'boxes does sound correct in this case if the diagram is correct or three if ECP is to be believe. They sell a cat, a and a back box with a centre section:

www.eurocarparts.com/ecp/c/BMW_3+Series_1.9_1999/p/car-parts/exhausts/car-body-parts-and-car-exhaust/catalytic-converter/?721110431&1&d6ffaa428dd8c43388ae8764737ce2ac8c577451&000059

www.eurocarparts.com/ecp/c/BMW_3+Series_1.9_1999/p/car-parts/exhausts/car-body-parts-and-car-exhaust/exhaust-parts/?702110111&1&00039dd4c17ceebbe0a071ee19e4719d3ba331a9&000536