Possible Compression Loss? (Edited from Rear Flange, see Post #6)
 

I've got an '04 base 8, 99930 on the odometer...here's my issue:

Pulled my cat off yesterday to find out if it was clogged - my 8 has been stalling out on occasion after I removed the upper intake manifold on an oil change a while back...found out I didn't have a cat thanks to the previous owner. Completely hollowed out, not a trace of metal in it. So I go to put the thing back on, but I can't get the spring/nut combination in the back (after the stock resonator) to tighten back on for me. 80+psi compressor and it just wouldn't budge. So, I'm running around with a two-part exhaust and it's super loud, and I don't want it that way obviously. It sounds like I'm running a v8, I'm past due on inspection and I don't want police attention. Any chance anyone has had this issue and can point me in the right direction? This isn't my pipe, but it is the flange I'm talking about:

Attachment 230489

Also, bonus question, if anyone's got a clue as to why I stall out and the car won't start upon occasion - only when warm - feel free to chip in. I've tried resetting the NVRAM and the KAM, but to no avail - my CEL didn't even go off.

P.S. Yes I have googled the site, no I didn't find anything, hence why I'm making this thread.

The OEM bolts is a stud with threads at each end and a smooth section between them. The spring sits around the smooth section, and gets squeezed between the cat-back flange (the studs point toward the rear of the car from the flange) and the nut.

If the nut is down as tight as it can be and you still don't have a seal, then you are missing something. Possibly the exhaust gasket? Actually different bolts? (common, due to rusting problems)



Trouble starting when warm is almost always low compression.

That doesn't look like a stock CAT/midpipe...unless they changed to SS tig welded flanges :)

What was on there before for fittings?

those flanges look like they were welded on a pipe that doesnt even look like stock cat converter. You might have trouble to fit it and youre gonna need a gasket in there. You might want o go to your nearest muffler shop they could fix it for you.

He DID say:
:)

I assume he actually has a stock cat.

This is correct lol. I took it to a Mr. Tire that I frequent often and they torched off the bolts and put new ones on for me, so issue solved.

As for whoever said I may have compression issues - what else accompanies that, other than warm start troubles?

Lots of issues show up from low compression:
- Hard to start when warm, no problem when cold
- Rough idle (also caused by ignition failure, vacuum leaks, MAF dirty, ESS fouled, O2 sensor failure, motor mount failure)
- Power Loss (also caused by ignition failure, vacuum leaks, MAF dirty, ESS fouled, O2 sensor failure, clogged cat)
- Poor gas mileage (also caused by ignition failure, vacuum leaks, MAF dirty, ESS fouled, O2 sensor failure, clogged cat)
- Stalls at idle (also caused by ignition failure, vacuum leaks, MAF dirty, ESS fouled, O2 sensor failure)
- Stalls as the revs are returning to idle (also caused by ignition failure, vacuum leaks, MAF dirty, ESS fouled, O2 sensor failure)
- Misfires (also caused by ignition failure, vacuum leaks, MAF dirty, ESS fouled, O2 sensor failure, clogged cat)

There are other more exotic issues too, but not really ones you are going to run in with a stock RX-8. Other engine failures possible other than low compression too, which would have some symptom differences.

Yeah, nearly every common problem we have with our car shares it's symptoms with nearly every other major problem as well. It makes diagnosis hard sometimes, but there are usually little exceptions for each problem that help isolate it, like hard to get it started when warm with no problem when cold is pretty exclusive to low compression.

I have all of this. My odometer is literally at 99,999 after running all my errands today. The car would not hold idle until I was sitting in my driveway, trying to catch it on camera in order to show it to you guys. It took me 3 tries to start on average, all warm...until in my driveway. I have power (e.g. it's not in limp mode), but it seems like when I hit 6K and the ports are supposed to open up, nothing happens. It just climbs slowly to 9K. Before this, it was giving me brief bursts of power, followed by split seconds of hesitation at certain RPMs, all in the upper half of the range. My gas mileage rarely climbs above 18 flat, and I do mostly highway driving with the usual redline a day coming home from work. But yeah, hard warm starts, no issues when cold, stalls at idle, stalls returning to idle, and I have been getting misfires recently.

I replaced the plugs, coils and wires at about 82K. I've been trying fuel system cleaner thinking that maybe my fuel pump was going bad, but I don't think that's the case. Hopefully this helps. I'll post that video if necessary/it would be helpful.

Edit: I wanted to clean the ESS because I read yesterday it might be screwing with things, but it's behind the air box (I think?), which I've never removed. It was dark out so I didn't try.