Help with PO420

dunowt

Hey all, i've just bought an OPCOM to try and get to the bottom of the PO420 code that keeps coming up. After running the diagnostics i'm getting the results below.......

and also after a few seconds it changes to this.............

I could do with trying to find out if anyone knows which is the duff Lambda or if its both or if its the cat? Could really do with it being just one of the Lambda's due to money being a bit tight at the mo! Can anyone help?

Cheers!

MikeS

if the rear lambda is pusling between .1 & .8 volts or near that then either it is running really rich or your cat is shagged

when cold the rear should hardly move more that .3-.6 volts and at fully operating temps it should sit around .7 at idle as your cat is effectively working

so i suggest you use opcom and record the voltage data from both lambdas at operating temps for about 2 mins and post it up [idle]

dunowt

Cheers for that Mike, i will try and post the readings tomorrow if i can find how to do it, i only got the OPCOM today.

MikeS

left button saying record

dunowt

DOH! Cheers.

dunowt

Hey all,
As MikeS requested here are my readouts,not sure if there are too many, hope this helps get to the bottom of it! :thumbup:

MikeS

when was this recorded

was the car idle ?

how long did u leave the car to idle before recording ?

dunowt

Hi MikeS, the car was idle it had been driven for about 15 minutes prior by the wife on the way home from work so the temperature was at around 85 C.

MikeS

[front lambda - mixture] voltage is hardly dropping below 250mv so looks like a lazy or faulty lambda thought first i would

look for air leaks on inlet manifold
leaks on cracked exhaust manifold / downpipe
clean throttle body
clean lambda sensor connector
clean lambda with carb cleaner

you want to see that lambda pulsing between .09v and .8v a few minutes after starting the car at idle - they tend to fail after they have warmed up a bit and become lazy

dunowt

Thanks for that MikeS, so if it is the front Lambda that is faulty is that why the second Lambda is all over the place trying to compensate? Sorry for all the questions just trying to get my head around it all????

MikeS

unplug rear lambda and watch your front lambda pulse and record results and post it up

the rear lambda will not severely effect how the front operates at idle plus a fault code wont appear for at least 10 mins

you have a standard cat btw ?

dunowt

MikeS said:
unplug rear lambda and watch your front lambda pulse and record results and post it up

the rear lambda will not severely effect how the front operates at idle plus a fault code wont appear for at least 10 mins

you have a standard cat btw ?

I will try unplugging the rear Lambda tomorrow and post the results Mike, the cat is standard with the precat removed. The EML normaly comes on after i have been driving for a while and then pull up at a junction or Traffic lights but its not constantly doing it i could drive 300 miles until it comes on and other times 60, the car also kicks a bit of smoke out at high revs but i dont know if that is due to it running rich?

MikeS

i wait till tomorrow for results 🙂

dunowt

No worries Mike thanks for your help so far mate i appreciate it! :thumbup:

dunowt

MikeS said:
unplug rear lambda and watch your front lambda pulse and record results and post it up

the rear lambda will not severely effect how the front operates at idle plus a fault code wont appear for at least 10 mins

you have a standard cat btw ?

Here are the readouts MikeS with the Rear Lambda unplugged hopefully this might help with your diagnosis!
Cheers!

MikeS

replace the front lambda m8 and look at difference

sake of 55 quid worth doing as it still looks like it is not pulsing right

get an NGK

dunowt

Cheers for that Mike wheres the best and cheapest place to get one from?

MikeS

most motor spares sell em

dunowt

Hey MikeS can you please have a look at the readout below and see if this Front Lambda is pulsing correctly? Its an old one i had got kicking around in the garage. Thankyou and Sorry for being a pain!!

This is with the rear unplugged.......

And this is with both.......