P0420 advice please !
- Thread starter kowsmou
- Start date
It's worth eliminating sensors, fuel cap seal leaking and intake hose splits but the 2.0 is prone to cracks in the exhaust manifold and has been the cause of similar problems for many forums members. IIRC the cats are integral with the manifold and leaving the issue will disturb the sensor readings, can cause fuelling issues and possible cat damage. There are loads of threads on 2.0 manifolds, many get away with the crack being welded, although it's a specialist job.
^^^This. Unfortunately the manifolds crack very commonly on the N46B20 (it fails at the weld where it joins the integral catalytic converter, usually on cyl 2). New manifolds with integrated cat >£1k as you have discovered but can be welded up for half that if you can find a decent garage to do the work. https://z4-forum.com/forum/viewtopic.php?t=13866
look at the fuel trims before spending out a grand for a new manifold cat,you may need to get a more accurate reader ..
that way you can see if its over fueling or under fueling,these engines are very sensitive to vacuum leaks, the cat may be clogged from this and may be salable. check your oil filler cap has a good seal,and you have the correct level of oil.
These engines also run a oil vacuum pump from the rear of the engine that can cause issues if its not performing well(blocked leaking ect).
if you do need a new cat there's a member on this site,ducklakeveiw.. who seems to be able to source second hand csts for this car
but do some tests on it first to make sure its the cats and not a vacuum leak.
hope this helpsi ve been there,
with my 2.0l
got told by stealers it was a buggered cat,but it wasn't,
that way you can see if its over fueling or under fueling,these engines are very sensitive to vacuum leaks, the cat may be clogged from this and may be salable. check your oil filler cap has a good seal,and you have the correct level of oil.
These engines also run a oil vacuum pump from the rear of the engine that can cause issues if its not performing well(blocked leaking ect).
if you do need a new cat there's a member on this site,ducklakeveiw.. who seems to be able to source second hand csts for this car
but do some tests on it first to make sure its the cats and not a vacuum leak.
hope this helpsi ve been there,
with my 2.0l
got told by stealers it was a buggered cat,but it wasn't,
never got to the bottom of it.like yours it comes and goes.
it passes MOTs on emissions.but bloody frustrating.
the garage changed o2 sensors and eventually the cat on warranty.
and it came back again.
ive heard even dealers state it'll probably come back.after changing the cat.
im gonna get back onto my car when the weather improves.
like you ive changed the plugs air filter and oil with no affect.
im aftrr a decent code reader.I currently use torque but it doesn't give enough information on fuel trims.
im hoping that will give me a better idea of whats wrong with it.
not much help sorry.
but I'll give you any information that I come up with
it passes MOTs on emissions.but bloody frustrating.
the garage changed o2 sensors and eventually the cat on warranty.
and it came back again.
ive heard even dealers state it'll probably come back.after changing the cat.
im gonna get back onto my car when the weather improves.
like you ive changed the plugs air filter and oil with no affect.
im aftrr a decent code reader.I currently use torque but it doesn't give enough information on fuel trims.
im hoping that will give me a better idea of whats wrong with it.
not much help sorry.
but I'll give you any information that I come up with