ArthurH

Good day all,

I bought my 2004 RX8 147KW with 106 000 km on the clock in April. I live in northern Germany. Before I bought it I've had them do a compression test and the results came back fine, no less than 7.0 (done at official Mazda Vendor here in Munster). I was told the car was fully serviced, new spark plugs, filters etc.
I've bought the car not as daily commute but for long trips, holidays.
I've hesitated for a while before making this post having spent a lot of time browsing the threads here, but none of the threads I've read exactly matched what I'm experiencing. The problem started in August:
I've noticed that it took a bit longer for the car to start, hot or cold. I was spinning but it wasn't igniting. The problem got progressively worse, and there really was no difference between a hot or a cold start, both took about 3-5 seconds. Then I had to drive all the way to Estonia, about 2300km, (before the trip I accidentally overfilled my oil by a fairly considerable amount) and on the way it refused to start at the gas station. It happened once, and then I got it going again and eventually reached my destination.
So I thought: spark plugs.
Finding a mechanic to service my RX8 was not easy. Nobody wanted to touch it.. Eventually I found a guy, he changed the plugs, said two of them were okay-ish, two were quite worn, all four were wet though. He also said when he put the new plugs in it started like new. But then the problem came back again.
Next I checked the air filter and it looked like it was NEVER changed. It wasn't oily, it was just clogged with all sorts of stuff. So I put in the new filter, had the airway and the MAF cleaned. It had a positive effect, but the problem didn't quite go away. Still took 2-4 seconds to start. The guys who cleaned the air way (at a non official Mazda Help centre) said they suspect that I'm running rich, because of the way it smells. And that that could be causing the slow start. They didn't know how to solve this issue or how it could have come about..
So then I had to drive all the way back to Germany and after about 3/4 of the way I see CEL. Checked it through OBD2 and it came up with u0073 ( Control Module Communication Bus 'A' Off) & p0420 (Catalyst System Efficiency Below Threshold (Bank 1)) codes.

I gather that u0073 can simply come up just by plugging in the OBD2 scanner, so fine..
p0420 is, I assume, a consequence of having had starting issues for a while.

The car drives fine, no loss of power. Normal oil consumption, mileage is only slightly above normal (16 L/100km town; 11L/100km highway). I do not premix.
So my questions are:
1. I get no misfires, so am I safe in assuming that the problem can't be caused by a bad ignition (plugs, wires, coils)?
2. I've read about the Coolant seal failure, and I have noticed white smoke on startups on a few occasions, but it's been very humid here so I can't be sure it's not condensation. Can burning coolant clog the CAT?
(Another thing that points to the coolant is this one time I was driving in the rain and a puff of white steam came from under the hood. It didn't last long, but it was noticeable. On visual inspection I've noticed no leaks though..)
3. Running rich. I don't even know where to start here. Can a bad air filter that's not been changed for too long a time make the computer go permanently insane and give me a bad mix? How can this be fixed? (The car does smell a lot of petrol behind closed doors for the first few minutes after I start it, but I heard that's quite normal.)
4. Could I in theory have lost enough compression in 6 months and 7000km to begin having these issues?

Obviously, I want to solve the core of the problem before I begin dealing with the CAT.
Help me establish a logical chain of thought, please!
I'm thinking of checking the pressure in the coolant system to rule that out first.

Arthur

UnknownJinX

I suggest having the ignition coils at least checked. They are a known failure point.

Also, how old is the battery? Get it load tested.

Are you losing any coolant? Is there any contaminant in your coolant?

BigCajun

iTrader: (1)

P0420 is a bad catalytic converter, usually caused by bad coils.
You could have broken pieces of strata blocking your exhaust, that would also lead to the strong fuel smell since the cat is bad.

The cat and exhaust behind it need to be inspected.
My concern with this is bad coils and cats are usually accompanied with misfires.
Misfires kill cats, bad cats kill engines.

If you have an Android phone, you should get the Torque app, it's a one time $5 USD charge, and a Blutooth dongle from Amazon, around $30.
You can scan codes and clear CELs, and monitor your OBD systems.
That can help you do your own troubleshooting.
Good luck!

ArthurH

I thought long and hard about the coils, but I'm not getting any misfires. Not even once. I'd be getting them if it were the coils, right?
The battery was changed a few years back, so I was told. I will have it checked.
If I'm losing any coolant then it's not a dramatic enough amount for me to notice.

ArthurH

I have the Torque app and the Bluetooth dongle, that's how I diagnosed the codes.
With monitoring the OBD systems, what specifically should I be looking out for?

BigCajun

iTrader: (1)

Stored and pending codes, 02 data, check for lean conditions to start.

BigCajun

iTrader: (1)

I would eliminate the cat as a problem first.
If it's bad it'll cause a lot of related problems, then check the coils.

BigCajun

iTrader: (1)

When mine went bad it was accompanied by misfire codes, that's why I'm suggesting the coils, cat and exhaust be checked out.
Idk for sure what besides misfires would cause the cat to go bad.
If the cat IS bad, then it needs to be corrected, then hunt for the cause.
If it is, you can gut it while you troubleshoot it to avoid anymore cat related engine damage.

BigCajun

iTrader: (1)

Maybe unrelated to the cat, the starter would be a good thing to check too.
A weak starter could cause repeated flooding, maybe the damage was already done when you bought it.

Loki

iTrader: (1)

Cat and coils. Don't wait for misfires to change the coils, unless you know they were recently changed. You have all the signs.

ArthurH

I really have no history of when the coils were replaced, so I know I will have to change them at some point in the near future.
Do you think dying coils can cause bad starts while not causing misfires?

ArthurH

Thanks for your suggestions, BigCajun!
I'm aware of the starter issue, I could still be running that infamous stock starter. But it seems to spin fine, it just doesn't fire!
As for the cat, it surfaced as a problem months after I began having those starting issues, so how can it be the catalyst of those problems? Unless it was bad all along, and the CEL came up after the fact..

BigCajun

iTrader: (1)

I guess it's possible for the CEL to come on after it's bad, but I'm not saying it is your problem for sure.
If you know it's bad, you have to start there, eliminate a known problem before you can get to the root of the issue.

Loki

iTrader: (1)

Yes, yes I do. Depends which plugs is affected and the nature of the failure. It's by no means conclusive, I'm not near the car, but the circumstances are all there: unknown history, hard starts, wet plugs, eventual cat problems. I imagine you can guess what the next step is... I would stop driving immediately until you can prove coils and cat are in good shape or new.

ArthurH

An update on the situation.
Had to pick up some gear from another town yesterday so I rather reluctantly started my 8.
The CEL has disappeared, (along with the DCS light that came up a week ago, forgot to mention that..).
What the hell? How can this be?
And it so happened that the day before I had made an appointment at the local garage o have the CAT and the coils etc checked next week...
This might be turning into a winter drama..

BigCajun

iTrader: (1)

Thanks for the update.
IIrc, when I was having my issues, the CEL was intermittent.

ArthurH

Update:
Took her to the garage to perform the CO2 test. Drove for an hour on the motorway to get the CAT real hot.
The results were awful. The allowed limit is 0.55, mine was showing from 1.5 to 1.9 so..very bad. Strange that the CEL had gone off though..
So instead of ordering a new CAT straight from Mazda for at least 1000 euro I got in touch with HJS Germany and they recommended HJS article 90950166 (connection 76mm) for me. It costs 550 euro. I read about the HJS cats on the forum and it seems people are happy with them. Has anyone had an experience with this particular article 90950166 though?
I also found some cheap options on ebay like this one:
https://www.ebay.de/itm/Walker-Katal...frcectupt=true

and this one:

https://www.ebay.de/itm/KATALYSATOR-...frcectupt=true

What do you think, fellow rotaries?

UnknownJinX

HJS is great if you want to keep a catalytic converter on at all times, including spirited daily driving, AutoX and tracking.

I use a 9095 0182 myself. I'd just shoot an email and double-check with HJS to see the temperature limit of 0166.

As for Walker, I know they make OEM cats for Honda, so it should be fine for inspection. You might want to take it off right after, though. No evidence of it lasting long for hard driving, and I know some Honda Accord owners who still have to replace Walker cats because their cars start to age and burn oil.

ArthurH

Thanks! I'm looking to keep the cat on at all times, so it has to be something reliable. So I guess nothing less than 500 euro can be of any serious consideration. I wrote HJS an email suggesting the 90 95 0046 model (I've read on the forum about it), and they came back saying they recommend the 90950166. Would you happen to know what temperatures does out cat has to withstand?

Loki

iTrader: (1)

I haven't paid attention to the cat temp on track, but in regular highway driving it can go above 900C. Plan a bit of buffer, so 1000C

UnknownJinX

You gotta ask HJS yourself. I only know that 0182 and 0190 have the optimal operating temperature between 250 and 650 C, has a maximum duration temperature of 950 C and a maximum peak temperature of 1050 C.

So far it has worked out for me. I do mostly spirited driving and occasional AutoX.

ArthurH

Alright! I've asked HJS about the three options (0182, 0190, 0166), I will let you know what they come back with.
I would need to replace the 02 sensors if I put in any of their cats, right?
Meanwhile, why do you think my CEL had gone off, although my CAT is clearly not operating properly and I'm at least three times over the CO2 limit (and stinking)? This just keeps puzzling me..

UnknownJinX

What was the code thrown? P0420 or something else?

If your old AFR(front) and O2(rear) sensors are fine, no need to replace them. If you get the wrong sensors, you could make things worse. I purchased some NTK sensors when I did mine and my gas mileage dropped from low(because I floor it often) to stupidly low and it seems like the car runs rich constantly. I changed back to OEM and it was all good again.

If you disconnected the battery, etc. then your CEL could have reset. Some people can run catless and never have the code thrown for some reason, while others get it quickly. It can be a bit random.

ArthurH

Yeah, it was P0420..
So HJS said 0182, 0190 can both be used but they say they do not know the dimensions of the vehicle ...?

The maximum peak temperature for 0166 is 1050°C.

I'm thinking I should just go for 0182 since it's already been tested by UnknownJinX, although it is like 100 euro more than 0166.. hmm...

BigCajun

iTrader: (1)

Cheap insurance weighed against the cost of a rebuild from another failed cat.