P0420 Code

[normanh]

Had the code show up yesterday during a 130 mile trip around the M25 yesterday avoiding Dartford Crossing, its a new catalyst type approved , new sensor no leaks in the systems as far as I know just after about 1500 miles, Any thoughts to reason please?

Norman

[Carolyn]

Did you use a Denso sensor?  Are the sensor connections all good?  Did you use new OEM crush ring gaskets when you installed the cat?

Just thoughts....

[normanh]

Denso sensor , new crush rings checked when installed absolutely no leaks! 2 Stainless A2 bolts/nuts and one stud. I have asked the supplier for his comments.

Norman

[Carolyn]

Have you just checked for leaks, or when the installation was done?  Tape a piece of tissue onto the ned of a long screwdriver and pass in around the joints (manifold to head and manifold to cat) if it flaps there's a leak. 

Were they OEM crush rings or aftermarket? I ask, 'cos the after market ones aren't reliable. 

Was the Denso sensor one with the connector plug attached or did you use a 'universal'?

[normanh]

Rings as supplied with the catalyst - needs again checking now for leaks when the rain and wind dies down, sensor Denso fully wired supplied by sparkplugs.co.uk.

Norman

[Carolyn]

Ah - those crush rings tend to fall apart.....  I'd replace with OEM ones (TCB has them).  also, make sure the grooves the rings sit in are clear of any debris.

[normanh]

Lets see if its the rings when the weather breaks. Strange but I am not noting any increase noise due to the joint blowing though.

Norman

[Alex Knight]

Your ears are probably much less sensitive to O2 changes than the lambda sensor I would suggest.

[Dev]

If I recall you had the same problem before installing the new Cat?
If so I would try the anti fouler trick to rule out a persistent electrical issue.

[normanh]

Yes I did have the problem before but the cat had done some 130K miles. It also was persistently close to failing the emissions test.

Just a thought where can the anti-fouler be sourced?

Norman

[Dev]

Yes I did have the problem before but the cat had done some 130K miles. It also was persistently close to failing the emissions test.

Just a thought where can the anti-fouler be sourced?

Norman

The diagnosis should be simple with the spark plug anti-fouler if you can find it. It will space out the O2 sensor so it takes a smaller reading of gasses that wont trip the 0420.  If it works then its a bad cat, if it does not then its some other cause. 

[normanh]

Oh I forgot I have emailed the Catalyst supplier - lets see what they say.

Norman

[normanh]

The catalyst supplier has suggested theres a slight leak in the joint. I have ordered new crush rings from MR2 Ben today. Had a chat tonight with my mechanic son who has confirmed that the old catalyst wasnt blowing, so I hoping to check it out on Saturday if possible. So no clear answers to date, too much wind today to check with a tissue paper!

Norman

[normanh]

Bearing in mind I cant get underneath the car currently I have ordered replacement crush gaskets from MR2Ben just in case. Tried the tissue test but it proved to be inconclusive today. I have been offered by the supplier to have the cat replaced and the existing one to be picked up at a later date which I believe is a good offer - only problem is I dont have any real time to get my son back on the case and swop them over.

Norman

[potge]

Most things have been discussed.
Have you done any logging with OBD on the 02 sensors?
This will at least confirm all sensors are working, in principle.
Principle is quite simple, pre cat sensors shall oscillate in a similar fashion, post cat shall be much more steady.

[normanh]

Replacement cat delivered today, just need the time to fit it now and return the the previous one back to the supplier, great service given here as his gonna pick it up when I have swopped them over.

Norman

[normanh]

Second catalyst fitted a nearly month ago and I have had 4 nice runs around the M25 comprising of heavy stationary traffic as per usual includes a couple where there was little traffic mid afternoon at 60/70 mph car still giving 45 mpg. Pull feels better as well as response at low speeds. The crush rings taken off from the first replacement cat showed no leaks or damage, no signs of blowing. Second replacement appears to be fully stainless no rusting to date.

My thanks to Gary from the supplier for persevering with me on the return of No 1 as it took some time to change them over.

Think the problem is finally resolved - I hope fingers crossed!

Norman

[normanh]

42mpg on an extended run on the M11/M1 at 60 -70 mph 340 odd miles, pretty pleased for a 21 year old motor.

Norman

[Chilli Girl]

42mph was slow for a motorway Norman Seriously though, that's brilliant. You wd've got even more if you'd done 50/55mph.

[normanh]

opps was 42 mpg

Norman

[2 of the left]

0420 shows catalyst efficiency below threshold on bank 1 replace your denso or your catalyst

[normanh]

Your a bit behind 2 - both had been replaced, 1st the sensor, then the cat, then the cat a second time, alls well now with the better second catalyst.

Norman