I am going blind to IVA having had emission issues when I tested on a gas analyser... We think the analyser was playing up but I know that Lambda is a
little unstable.. I was going to take a chance and go to IVA and take my laptop... Rather than try to tweak the fuel map I was thinking that I
could change the target lambda to lean the whole map up if I fail the test... Anyone know if this is a good idea or not?
Thanks
Dave B
I've been dwelling with emissions problems from quite some time with my car now being under a small rebuild process.
From my experience what really help was to fit an afr sensor with a gauge on the dashboard this way you could check if the air to fuel mixture is too
lean, too rich or perfect at the different tps positions on real time, checking and correcting before iva to be on the safe side!
All the best,
Nuno
Make absolutely sure there are no air leaks on any exhaust joints, even a slight leak can give a high lambda reading, even if the emissions are
perfect.
The Cat will have little or no effect on Lambda ie: the Lambda will be the same before and after the Cat, the only change will be to emissions.
A very good diagnostic chart here. Go to: Tech things to know> exhaust emissions> using lambda
A tiny leak in exhaust especially the later sections will give high MOT test lambda readings as it draws air into the exhaust.
The main purpose of the Lambda test is to stop bodgers getting through emissions tests by making holes in the tail pipe to dilute the exhausr gas
with air.
Last week I had a car fail on high lambda, I couldn't find any hole in the exhaust even putting a rag up the tail pipe but when cut the old
exhaust I found a few really tiny holes in one weld. I fitted a new system post the secondary cat gave the car an Italian tune up to burn off any
paint inside the exdhaust and the 12 year old car sallied through the emission test with the lambda right in the middle of the accepted range.
Incidentally the exhaust was the one piece system fitted by the Longbridge factory in 2002 :-)