Problems With 2000 Corolla Ce - Toyota Corolla, Chevy Prizm (1998-2008)

So, long story short, my exhaust is chopped about 4-6 inches after the resonator, i didn't want it chopped but it ended up happening and is a long story that i don't have the patience to get into..

Anyways i seem to have improved my engine, i can't really tell how but i have and i like it. However, my muffler is now ridiculously loud inside the car (i don't care about the outside noise level as much), and i now have a CEL reading P0420 which means catalytic converter is not working efficiently (most definitely from the loss of back pressure so the CC doesn't have enough time to clean the air before it gets out). But the loss of back pressure might not be the culprit. I just replaced both upstream and downstream O2 sensors. but what boggles me is that i got my car smogged about a month before the exhaust chopping/O2 replacement and it passed.

does anyone have any *CHEAP* ideas on how to quiet my car?

anyone have any *CHEAP* ideas on how to fix my the P0420 problem?

any ideas are helpful and well appreciated.

Also i have another problem. I have moved this problem because it is more important and needs more detailed answers. so here's the deal. My car drinks oil for breakfast. i have to refill the oil anywhere from .5-1 quarts every 2 fill ups (not sure what kind of gas millage i'm getting but everytime i fill up i'm putting in atleast 10 gallons to 11.5 so i put a product called "Restore" in my engine and it seemed as though my car got a lot peppy-er but when i then changed my spark plug platinum +4's i noticed that the two middle spark plugs had oil all over them. especially the middle left spark plug. anyone have any idea what's going on here? i've heard a lot about gunked up oil control rings but i've put almost every additive i can think of into my gas tank and my engine oil to loosen them up and have them make a better seal.

The additive might be compounding the issue with oil control. Something like Restore "might" help, but more likely to gum things up and make the oil consumption worse. Best to keep using a good detergent and additive package motor oil, shorter oil change intervals, and keeping an eye on the oil levels. Don't add oil additives, as many work against the additive package in the motor oil. True, that the majority of the ones with oil consumption issues find stuck rings in their pistons and/or damaged rings. Varies from engine to engine, some have gotten away with cleaning the engine out - others had to swap in a used engine or rebuild their current one.

Plugs - switch back to iridium plugs. The multiple prong plugs on the 2000+ models have shown intermittent operation, many have run into misfires running those plugs. If they misfire, you can load an excessive amount of fuel into that cylinder, leading to oil consumption issues. As for the oil on the plugs - it is on the electrode end (part that goes into the combustion chamber) or is there oil on the threads/pooling inside the spark plug well.

If oil on the electrodes, likely those cylinders are the ones that are burning oil - run a compression test to see what each cylinder is doing. Compression should be 145PSI-218PSI, with no more than a 15PSI difference between cylinders. Repeat with a wet compression test, see what the numbers do. A leak down test might be in order, depending on the results of the compression test.

If oil is on the threads/exterior of the plugs, likely you have an oil leak on from the valvecover gasket. Each of the plug tubes have their own o-ring, those can dried out over time/shrink - causing oil to pool in the plug well and wick into the threads. Can also lead to misfires that will foul the plugs.

For the exhaust - most of the noise suppression is from the muffler and the extra length of exhaust piping cooling the exhaust. Not much you can do, unless you want to stack resonators. Some have found that running two resonators inline (resonator is basically a glass pack muffler) - they can quiet down the exhaust a bit. Also depends on how the exhaust is exiting the resonator - just down under the car, have a shorty tip that points to the side, etc? If it dumps under the car, you're going to get an impressive amount of noise transmitted to the cabin, as the exhaust noise is basically bounced right off the road into floorboards, then into the cabin. Might help to turn that exhaust away, run it out the side, even running it through a shorty muffler (sometimes called turbo mufflers, usually about a foot or so in length, minimal chambering, but quieter than resonators.

P0420 - don't think of the shorter exhaust as back-pressure, more of exhaust scavenging. Shortening the length definitely changed the resonance of the exhaust - so you could be hindering or helping exhaust flow. You can "trick" the rear O2 sensor by running a spacer between it and the exhaust pipe. One common way is to drill out the end of a spark plug defouler, screw that into the exhaust bung, and then the sensor into the defouler. That allows for a dead space for the exhaust gas, making it less likely to trigger the CEL.

As for being peppier in driveability - hard to say. Shorter, open exhaust do benefit WOT applications, so if you have a heavy foot, it will seem like the car is more eager to rev, get up to speed quicker. Most find that a particular exhaust mod has a sweet spot in a certain RPM range - probably what you are feeling at the moment. The real trick is to have that sweet spot cover a wider RPM range, especially around the thick part of the power band.

Well.... it was mostly on the top of the plug/ socket nut part (I don't know what it's called) and the porceline(SP?) part. But I think that the "Restore" helped seal it up a bit cause I've had 2 fill-ups since then and I haven't lost an ounce of oil. The valve cover gasket is $16 at kragen and my car club will help me replace it super fast..

Now, what should I do when I have the valve cover off? Any cleaning/scrubing of valves or the cover or additives I should add? Suggestions/ideas are helpful!

If it on the top side of the plug, definitely sounds like the sparkplug tube o-rings are leaking.

Once you have the valvecover off - might as well take the time to measure valve clearances. Also gives you a good idea of any potential sludge or backed on oil. I wouldn't scrub the cams, or you might end up damaging the bearings - but it does hurt to clean up the valve cover itself really well.

Also, I suggest NOT stacking additives. Run one additive, let it do its thing, and monitor what it does over some time. If it looks like it is not working as expected, then try something else - always leaving time in between to see what it is or not doing.

Oh yea of course, that's common sense... but I bought the valve cover gasket at kragen and plan on changing it VERY soon, how would I go about meaduring the valve gap or whatever you said?

Sorry, I know a lot about corolla's but as far as the engine goes the only thing I know about it is oil, oil additives, and everything attached to it, but I know nothing that involves going into the engine(engine block, valves, cylinders, etc.)

I also wanted to know a little bit about the brake booster, if their is a thread or website that has a diagram/schematic and information on it I would really appreciate it