For 1996 and later vehicles the test stations just plug their computer into the vehicle's and check for abnormalities. For older vehicles they take actual exhaust measurements at idle and cruising speeds, but the standards for those are much more lax than the ones the manufacturers have to meet, especially for pre-1981 cars.
Pulling the cat isn't going to get you much in terms of mileage or performance. Any performance gains will be small (on the order of 2 to 3 HP) and are likely to be in the upper RPM range at the expense of lower RPM torque. Back pressure isn't always a bad thing - especially for a street-driven vehicle. New cats are pretty good in regards to back pressure anyway. There's not much to be gained.
Anyhow, you'll have to put the cat back on for your bi-annual smog check so why bother?
Peter
In California, most smog stations now have a computer-controlled rolling dynamometer where emissions are checked while the car is "driven" over a prescribed course. As well, the tech conducts a visual check of the smog equipment.
Peter
Well, not as many as there used to be, that's for sure.
I've been looking for independent shops, but the two I've tried so far don't deal with catalytic converters. The reason I've heard is that people around here buy new cars faster than they go through converters, so the stock just sits on the shelves and ties up money.
Now, to find a decent parts shop that does catalytic converters...
Thanks for the response.
Thanks Everybody for the replies. It appears that the age of the car makes a difference. If no O2 sensor is placed after the cat then the air/fuel mixture will probably not change. If an O2 sensor is placed after the cat things will probably not work the same. Eric
On Wed, 13 Sep 2006 03:01:15 GMT, with neither quill nor qualm, Gunner quickly quoth:
Yeah, send him home with MY cat, too.
- If the gods had meant us to vote, they'd have given us candidates. --------------
Wrong. My 1999 Van just had to start getting smogged, after an automatic 5-year exemption period. The only difference might be where you live - I'm in Los Angeles County, in a rural county where they don't get quite as involved they may skip that.
They put it on a chassis dynamometer to put a controlled load on the engine, stuffed the exhaust gas analyzer probe up the tailpipe, pressure tested the gas cap for worn seals or bad relief valves, and hooked the tester's computer up to the OBDII Port to interrogate the computer status and watch the emissions test from the engine's POV.
And clearing the computer memory to turn off the Check Engine light immediately before driving to the smog test location will NOT let you get away with anything - the computer memory will be flagged because there will be no record of a successful drive cycle with all systems acting normally. They will not complete the smog test at that time, they tell you to come back in a few days when the computer has had a chance to either set that flag or pop the CEL on again.
It takes two successful drive cycles back-to-back to set the internal "All is Well" flag, and it would catch the bad catalyst, bad charcoal canister, leaking vent hoses, etc. by then. It's 'you HAVE to get it fixed, or else' time.
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Even without the second O2 sensor you still need a working catalyst to pass. They will get the engine warmed up, on the dyno driving under a load, and then put it in an over-run condition (get off the throttle while moving at speed).
If they see a huge spike in unburned Hydrocarbon emissions, it fails
- they will know the catalyst is missing or toasted, because the excess fuel should have burned up when it hit the catalyst.
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On Wed, 13 Sep 2006 16:35:12 GMT, with neither quill nor qualm, Gunner quickly quoth:
Despite the fact that I love cats of all sizes (I just don't want them around) I consider that allergy to be genetically advanced metabolism.
-- Nothing is a waste of time if you use the experience wisely. -- Rodin
Greetings Bruce, My argument with my neighbor was not about emissions or legalities. It was about engine performance and effiency. He said that on any vehicle removing the cat would result in better mileage and more power. I said that this may be true of "performance" cars but not true generally. ERS
I'm not in California, and the testing standards here aren't nearly as strict, and in some parts of the state only steady-speed tests are done, even on vehicles as new as 1995. I learned that 1996 and later cars weren't measured at the tailpipe but simply their computers read out when I asked how they dyno tested full-time AWD.
I stand corrected on that.
On Thu, 14 Sep 2006 05:19:57 GMT, with neither quill nor qualm, Gunner quickly quoth:
Well, it's good to hear that you feel good about yourself, son. ;)
-- Nothing is a waste of time if you use the experience wisely. -- Rodin
Of course I do. Bright, common sensical, smart, not allergic to cats, a decent wing shot and accurate with a rifle or handgun, able to leap tiny fences with a single bound and still kick a lightbulb out of an 8' ceiling. (though Im laid up for a couple days after..sigh..)
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3
Not true generally - there is a point where you have 'too much of a good thing' and the exhaust system backpressure gets too low, you need a little to make it flow right. Especially on a normally aspirated engine. The 'extractor action' of the exhaust manifold is designed so that the exhaust pulses from one cylinder create a partial vacuum to pull the next cylinder in the firing order.
Dragsters and Funny Cars can get away with running "Zoomies" with practically no backpressure (just a curved length of tubing off each exhaust port, aimed in a safe direction) because they have a supercharger forcing the air and fuel into the cylinders in massive quantities, some of which goes straight through due to valve overlap and gets wasted.
That raw fuel pass-through hurts the overall efficiency, though it does make for lovely gouts of flame coming out the stacks at night...
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On Fri, 15 Sep 2006 08:44:25 GMT, with neither quill nor qualm, Gunner quickly quoth:
Typical Downs reply.
It's hell getting old. I'm stiff all over (girlfriend liked that part) after putting a threshold in an old log cabin yesterday. Grok the "laid up" part.
P.S: How's that book coming? ;)
Been on the road all week. Came home a day early to take delivery of the Albino Amazon...and start rewiring. Its a bitch without a schematic...and there are wierd shit things like what appears to be a rudimentary computer. The hand throttle..is a box with a pair of photocells inside..and a disk that comes up between them. Evidently the less light it sees..the more power it sends to the throttle solenoid..
It couldnt have beens something simple like a potentiometer..oh f*ck no.... $%#@! Germans.....
Ill start on it tonight.
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3
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