Just bought a RX-8 nemesis and have code P0420

[Srobo]

Hi guys and girls.
I’ve just bought an RX-8 nemesis which developed an engine management light on the way home.
I’ve plugged in my obd and it comes back as P0420 catalyst system efficiency below threshold bank 1
I’ve read that this could be anything from a new cat to o2 sensor to a leaking vacuum pipe? Any ideas on how to diagnose?
I’ve not jacked it up and had a good look underneath yet, I’ll do that tomorrow, anything I should look for when I do?

It ran beautifully up until the light came on then started running a little rough and developed a whirring/whistling noise from the engine, I don’t know if this has anything to do with the code or not? I’ve read somewhere that it could be the air intake but I’ve checked the filter and cleaned the maf with no improvement!

Any help would be appreciated and apologies if this is in the wrong place!

[GreySilver Beast]

Hi & to the RX-8OC

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[Srobo]

Hi & to the RX-8OC

<<<<<< Please put your Location in your Profile Box, it will help us to know where you are, if required any help in the future

Please check out the EVENTS SECTION's for anything coming up soon in your area

Events Team

All done

[Shagrington]

Hi and Srobo. You are right, that code could be any one of many things - how to diagnose which it might be is beyond my own skills ... if it is any help (probably not) I got the same code on my way home from the club AGM in February - the light came on as soon as I got on the motorway so I stopped in the next services and read the code. As it was that code I cleared it and carried on thinking I should be OK to get home and if I got a repeat I'd get it checked out. It hasn't happened again ever since ... but that is just me and my car.

Have a good read through whatever in the FAQ section you didn't already read and then (and just ignore me if you know all this already) here are my best tips for keeping it all running sweetly:

1. To start up turn the key to position 2, wait for most of the lights on the dash to go out (I watch the airbag light by the glove box), press the clutch to the floor (optional, but reduces drag), turn the key to start and do not touch the throttle until it has started. You can drive off straight away, just keep the revs down for a bit (see #4 below).

2. Never turn off the engine before it has reached at least somewhere towards normal operating temperature (should only take a minute or two, but best to go for a short drive if just swapping cars round on the drive etc). Switching off cold risks flooding, which is a real with a rotary engine. Mazda recommend rev to 4k and hold it for 8-10 seconds switching off while still revving if you have no option but to switch off cold (it is not necessary to do this in any other circumstance).

3. Check the oil level regularly (use the dipstick - the oil gauge tells you nothing other than that you have or don't have pressure) and top up if necessary with semi synthetic 5w30 (most people and specialists are advising to use 10w40 now though) ... small amounts at a time, no more than ½ a litre then check the level again before adding more as you don't want to overfill it.

4. Use all the revs once the engine is nice and warm (don't sit idling to warm up, start up and drive but keep it below about 4k until the needle on the water temperature gauge is pointing straight up, then give it another 10 minutes for the oil to warm up too before really thrashing it ) and hit the beep often. Best acceleration is from 4k revs up - to pull away you really need to rev to 2k - you can let the revs drop after lifting the clutch if you are in traffic, cruising steadily at 3½k revs and changing down to go up hills or accelerate gets you the best mpg ... which still won't be great.

5. Join the club for discounts on all sorts of things (you will very quickly get the cost of membership back - and then some), loads more info in the members only sections (including access to all the workshop and technical manuals), local meets (when we start them again, they're currently all postponed for obvious reasons - if you can't find one exactly local it is a good excuse for a drive if you come to one a bit further away), a sexy keyring just for joining and more.

[Juey]

P0420 usually means it's been decatted. Have a look at your exhaust system underneath and see what mid pipe is fitted.

[Dave2112]

Hi there, welcome to the mad world of rotary as said above the code relates to the cat or lack of? I would also look at changing the coils, leads and plugs. I can’t stress enough how important this is for a rotary engine. But don’t buy cheap eBay ones. Go for genuine Mazda or as an upgrade look at Ryan rotary coils

We have a monthly meet the second Thursday of the month, which is this Thursday. We are meeting at the viewpoint car park up by Crickley hill, at 7:30. Come along if you would like to and we can have a look T your car and give you any pointers. We will be going for a drive then to a butty wagon for something to eat.

See the Cotswold all sorts thread for more details

[Ollie]

I think that code can also relate to longish motorway drives where the car actually gets a proper chance to check the cats efficiency if I'm not mistaken? Some people get it once (had it once myself) turn it off and then never see it again without the cat being dead.

[qwakers]

other way round

the code relates to a missing or defective cat, however the car can only test the cats efficiency under certain circumstances, hence the code only appearing on long drives.