Freq

04 MT.
My mechanic says that it starts fine, but after warmup, starts running bad and dumps fuel to the point where the cat starts glowing.
Since it seems to be running as it should upon startup, cld this be a closed loop issue? From what I've read, the rx8 employs closed loop after the o2 sensors warmup and a static fuel map prior to warmup.
..and if it is a closed loop issue, could it be that the overheated cat cld've caused damage to the o2 sensor in the cat which is causing the closed loop issue?

--trying to figure this out because my mechanic has no idea what's going on-and will continue to charge me for swapping out parts instead of accurate diagnosis.

9krpmrx8

iTrader: (46)

If the cat is glowing, it is bad and needs to be replaced. Get a new "mechanic".

Freq

I know the cat needs to be replaced, and I know I need a new mechanic.

I could put another cat on the car, and 10 minutes after starting it it's slagged again. That's a quick way to 'burn' $1400 spent on a new cat.
..and obviously, if I'm asking these sorts of q's, then my 'mechanic' isn't up to par as all I shld worry about is paying the bill.

I don't want to put a bandaid on this, I'm trying to find the source of the issue.

9krpmrx8

iTrader: (46)

The issue is that your cat is bad. If your car has a healthy ignition system then there is no underlying issue, you just have a bad cat.

Freq

I understand why you'd say that. I assume that in similar posts, the cat would've been on since 2004 or so and bad coils would have killed the cat over time.

This isn't the case in my situation. I handled that last year when I put a new cat and bhr coils/wires, etc on the car.

In addition, the mechanic, rather than accurately diagnosing the underlying issue, put another cat on the car. So the cat that is currently glowing red has 0 miles on it.

So, we have a *brand new cat*, start the car, runs as it should until it warms up, then starts running rough and then the cat starts glowing. The mechanic says fuel is being dumped. I agree as it's not burning oil and it would have to be running **extremely** rich in order to light the cat up in minutes.

So, my question is (and b4 someone says coils, the car has new coils/wires/plugs as this mechanic has seen fit to *replace* instead of *diagnose*) what could cause the fuel to be dumped--cld this be a bad o2 sensor? Possibly bad fuel injectors?

Loki

iTrader: (1)

What are the fuel trims?
Is it running open-loop or closed-loop?

If they're high, the computer is adding fuel because it thinks there is more air coming in. If the trims are near 0, the computer thinks its giving the right amount of fuel, but the O2 sensor is lying.

Get some data

Freq

I unfortunately don't know how to get that info. Do I need special equipment to get that data?

Loki

iTrader: (1)

An OBD reader (you mechanic should have one). You can order one on amazon, they're about 15 bucks and pair with your phone via bluetooth.

Freq

Thanks.
Outside of resetting the trims via brake stomps or disconnecting the neg batt cable, how wld incorrect trims be adjusted? Would need to drive it to have the computer relearn? -and if so, I guess wld need to unhook the cat to do it without risking damaging the engine?

9krpmrx8

iTrader: (46)

If you have out of whack fuel trims then it could possibly be a vacuum leak. Your issues need to be properly diagnosed by someone who knows what they are doing.

Freq

..and that's the crux of my problem, which is why I'm posting the questions. Neither my mechanic, nor anyone else around here (including the mazda dealership) knows what they are doing.

9krpmrx8

iTrader: (46)

I find that hard to believe in Boston. They don't have to be a rotary specific mechanic, just a decent technician.

Brettus

iTrader: (2)

Has the engine ever been replaced ? If so they probably put the p1 and p2 injector plugs on the wrong way around .
I would be seeing what the afrs and fuel trims were before replacing parts . Hard to believe your mechanic doesn't know that .

RX8Soldier

iTrader: (24)

This is why you should keep all your questions relating to this topic to a single thread. We're trying to learn what you have/ have yet to do to diagnose, and your posts are spread throughout multiple threads. It's as though we're responding to you for the first time, every time. Stop creating multiple posts on this subject.

That out of the way...


As others have said, get data by hooking up to OBD2 reader. Get the codes and report those numbers. If there are no codes, post the data that your reader provides

Brettus

iTrader: (2)

I see he did replace the engine per one of his other plethora of threads . In that case I would say he definitely should check injector plugs!

Freq

Understood and apologies. For ease of search reasons(I would assume), some forums would rather you ask specific questions in specific threads as opposed to 1 general thread with numerous specific questions in it. I didn't want to waste people's time asking something like 'my car wont start-why?' - I didn't really need that (general) level of diagnosis.

Freq

I think this new question needs its' own thread, but per RX8Soldier's request, I'll keep it in this thread ...
I just spoke to the owner of the shop. He says that the engine's compression is too low. Says it is 70 psi when warmed up over the 6 faces of the 2 rotors. Asked him why did he say it was high 90's initially and he said that the compression was checked when cold, but he didn't think to check the compression when warm.
So my question regarding the above are as follows:
Is it possible for an engine to drop 20+ psi after 5 minutes of warming up?

9krpmrx8

iTrader: (46)

A compression test should be done with the engine at operating temp.

Freq

Understood.
Is it possible for an engine to drop 20+ psi after 5 minutes of warming up?

9krpmrx8

iTrader: (46)

Possibly, but no one can say for sure. But people (including dealers) doing compression tests wrong is nothing new. People are lazy, especially mechanics.

Freq

K. Thanks for that info.
Assuming the mechanic is correct and it's 90 something psi cold and 70psi warm, am I correct in assuming that the engine is borderline too low compression to run reliably?

Also, the mechanic is trying to say that the low compression is the cause of it running rich. Do you think that is likely?

9krpmrx8

iTrader: (46)

70psi is abysmal and so is 90psi.

Loki

iTrader: (1)

What rpm is that 70 or 90 at? It's pretty bad either way, but if your starter is only turning at 150rpm, that certainly explains why it's that low. If the mechanic complains about having to retest to get that info, you can invite him to research how a rotary builds compression on his own time.

But also, low comp doesn't explain why you're getting all that extra fuel. Get that OBD data :o

Freq

Y, going to talk to the mechanic again this afternoon. The mechanic says it idles fine before it warms up (in open loop), but then when it goes into closed loop, runs like crap.
Closed loop depends on the o2 sensor. My current (possibly invalid) theory is that the super heated cat may have fried the o2 sensor which would then cause the fuel to get dumped after warmup when the fuel trims are relying on that o2 sensor. I'm still researching, so not totally convinced of that one yet.

Brettus

iTrader: (2)

Typically when an O2 sensor fails , you see the afrs flatline at 14.7 , so it's pretty easy to spot. They don't tend to just go out of adjustment ,although that can happen, it's not common.
Low compression doesn't make it go rich.
Also , I'll say this one last time ........... check the injector wiring !