I don't work on cars but have tinkered with my civic a bit, so I'm not really sure how to solve this problem the right way, or the simplest way. I don't have the cash to spend on repeat visits to an auto shop either, any possible repairs I'll be doing myself.

The emissions data is (TX):
@2500rpm,
HC ppm - 165 (220&gt
CO% - 2.9 (1.2&gt
CO2% - 12.8
O2% - .1
NOX ppm - 0.0
Dilution% - 15.7 (>6)

@805rpm,
HC ppm - 306 (220&gt
CO% - 1.12 (1.2&gt
CO2% - 13.9
O2% - .2
NOX ppm - 0.0
Dilution - 15.0 (>6)


My suspection is that my cat is hollowed out, I recently purchased the car from a neighbor who has done some exhaust work on the car. I tapped on the bolts (with a screwdriver) on both my brother's 94 accord LX, and my civic and mine seemed to have a more hollow sound to it, or a deeper sound from the tap. It also has a deep throaty sound to it, which may be because of the aftermarket muffler. Unfortunately the previous owner doesn't speak english so asking him about the cat is not really an option [:@] I took it back after changing plugs and air filter which helped a small amount.

Also when I start the car with the door open I can smell the unburnt gasoline (not as bad as my older brother's 98 twin turbo supra, that has no cat), but the car doesn't seem to be running poorly at all. 5spd manual, 164k miles, aftermarket exhaust (unknown which) and a possible hollowed cat (my suspection).

Unsure about O2 sensors or vacuum lines (I checked them for cracks, holes or any other damage and seemed fine), as I get no service engine light.

Should I unbolt the cat to see if it is hollowed out?

 

go for it. it's pretty easy. you should only half to unbolt the exhaust side of it to tell. unbolt the exhaust side of the cat, grab a flashlight and push the exhaust piping out of the way, and take a look.

 

Will try that tomorrow for sure.

 

Am I interpreting the data correctly by saying that the CO is too high at 2500 rpm and the HC is too high at 805 rpm? If so, I don't think the cat is the problem as the NOx is not high. Instead, I think the engine is running rich. Begin by checking for a crack in the exhaust manifold and a bad O2 sensor. Even though the CEL is not ON, check whether you can retrieve a code from the ECU (see link in my signature).

 

I checked for that jumper cable, couldn't find it but I did find the SRS cable

Will check exhaust manifold tomorrow when I have some daylight.

 

Look for the connector above the ECU. It branches from the main wire harness.

 

Does the engine warm up to normal temperature halfway up on the gauge? Unless and until the engine warms up it will run "open loop" which makes it rich and it will fail on HC or CO. Could be a bad, removed, or wrong thermostat.

If it's not that, probably the O2 sensor. You should check the cat as well anyway though just to be sure.