Hey guys, I'm trying to diagnose a problem but I'm not getting any clear cut signs (at least in my weekend mechanic experience). Any help is appreciated.

I have a 2000 HX w/ ~150K. Only mods are an intake and suspension. I've been doing regular maintenance on it (including plugs, plug wires, fuel filter, air filter, rotor & cap). My gas mileage used to be pretty good, but within the past month or two it's dropped about 8 mpg. The only code I've thrown is for the Primary O2 sensor, which I replaced along with the sensor after the cat. The car has been running fine (no shaking, no low/weird idle) in spite of my loss of fuel efficiency.

Two days ago my CEL came on and I got it scanned and it was for the Primary O2 sensor. Car was still running fine so I had the light cleared to see if it would come back. It had stayed off so far but today as I was driving back from the store my CEL started to flash. The car was still running fine so I just hurried to get back home (only half a minute away). No codes were thrown and it starts up and runs/idles fine still.

I've been trying to research the loss in my mpg, and it seems like it could be a possible cat failure. But I'm not getting any clear symptoms of one (at least what I've read online - Smells like eggs, cat rattles, sluggish [Hard to determine in my car h:], etc...).

So if anyone could throw out a good suggestion of what I could do/check, I'd much appreciate it.

 

If by failure you mean the internals have packed up and are clogging the exhaust flow, you'd almost certainly notice the difference, at least at WOT.

What brand of O2 sensor did you use as replacement? I've read nothing but bad about the Bosch ones. NTK or Denso would be my first choices, followed by NGK.

 

I'll try the car at WOT. I never really get on it, but I'll try and see if I notice a difference. Will the difference be night and day? I don't believe I've driven a car where the cat is clogged or anything so I'm just somewhat clueless to look for in this situation.

The O2 sensor before the cat is NTK, and the one after is Denso.

Thanks.

 

I've also never driven a car w/ a cat. that was that bad, at least not that I'm aware of. I wasn't sure what you meant, if the cat. was just no longer doing it's job, emissions wise, it might cause a CEL but shouldn't drastically change the way the car drives - I wouldn't think.
If it's falling apart inside though, and is now blocking exhaust flow, it won't want to rev, no top end. Being an HX though, only someone familiar with the car, like yourself, might be able to tell the difference h:

 

Well I took the car out today and of course, nothing seemed wrong. I took it out on the freeway and it's as fast as an HX will be. No problems at all accelerating or idling, and no lights whatsoever. But I dunno. I'll keep driving it until something else comes up. Hopefully my mpg will be the only thing to come up. :madr:

But thanks for your time and input. I do appreciate it.

 

No problem, hope the mpg picks up, especially as it's an HX