After 2 pre-inspections and 4 smog tests my car finally passed. Here's the mods I have done to my "91" LO3 with 94,000 miles on it: Ultimate tbi mods, 14x3 Open Element flat base with K&N, SLP Y-Pipe (connected to stock exhaust manifolds), Random Technology Cat, Flowmaster crossflow muffler, Taylor Spiro-Pro 8mm plug wires, AC spark plugs and new cap & Rotor. Before I had the engine tested I did a Full tune up: cap, rotor, Plugs, synthetic oil change, new 195* thermostat, checked Timing at 0* factory setting and put on the stock air cleaner assembly. Here's what I learned: 1) HC failures are a result of an incomplete burn in the combustion chamber as a result of a to rich or to lean air fuel mixture (in my case too lean). 2) CO failures are usually a result of not enough air entering the engine. 3) NOX failures are a result of hot combustion temperatures. Usually caused by the EGR valve or catalytic converter not functioning properly. My engine failed HC and NOX the first time so I increased the fuel pressure to 14psi from 12psi and after the re-test the HC passed but the NOX still failed. To try and solve the NOX problem I replaced the EGR, PCV valve and put on a new Car-Sound Cat (because I thought the Random Technology Cat was not functioning right) but, still failed the re-test. After talking to my mechanic he recommended a Smog pre-inspection station that checked out the engine and informed me that my engine did not have enough back pressure for the EGR valve to function properly. He said the EGR valve needs a certain amount of back pressure to recirculate exhaust gas back into the combustion chamber which cools it down a bit and reduces the NOX levels. Finally, the smog pre inspection guy got the engine to pass but, only after revving the engine up just prior to testing. He said revving the engine heats up the Cat more effectively than just idling. I had to have the car tested again at a Test-Only station and it failed again because I couldn't rev the engine before the test. I finally took the car to another Test-Only station that I normally use and the guy there let me rev the engine before he tested it and it finally passed. Hope this helps someone else.

Good info, thanks for the update.

RBob.

damn smog nazis

That sounds like too much work/money to me. You spent the cash on a Random Technology cat, just to replace it? That sucks. Then you still had to (what many would say) "cheat" to get it to pass. I feel sorry for you man, because if I was in California I would not have all the things I enjoy about my car.

Well, at least after comparing the two Cats, it looks like the Car-Sound Cat is designed a little better than the Random Tech Cat just because the Catalyst Matting on the Car-Sound Cat is recessed flush with the converter body where as the Random Techs Catalyst Matting sticks out about 1/8" into the exhaust flow and doesn't wrap completely around the honeycomb catalyst leaving about a 1/8" gap as you can see from the picture. Otherwise, the two Cats look and perform identically.

Car-Sound Cat= $119 installed
Random Technology direct fit Cat= $229 plus installation (if needed)

I am dreading trying to get my new engine to pass AZ emissions in a few weeks. Still have not put it in the car, but I know I wont be running EGR, still have the CAT though.

Has anyone tried that stuff you put in your gas tank that guarantees that you pass? I have seen it at checker auto just wondering if it works. Anyone have any tips/tricks for passing?

Hey JR, I'm using that stuff that guarantees you pass emissions, its called Pro-Tec. I have to get mine tested before the end of April in Chicago, so I can let you know if it works or not.

i have taken carbed cars and ran them on alky and brought them to the stations in mas passed no prob the guy could not understand how a car that was just about all out drag could pull it off

Try header wrap, or ceramic coating the exhaust between the heads and the cat. Not only will that make lower under hood temps, but it will increase cat temp dramatically at idle, helping it function better. I know you already "passed" but that is a way to get it to pass legit next time.

i've heard some guys saying to use Denatured Alcohol stuff you buy at Home Depot, it doesnt eat awya at your fuel lines and rubber parts like rubbing alcohol does. just as soon as i get the valve stem seals replaced and my new headers on i'll be getting tested.

alcohol? How would our TBI engines even run on that stuff? I thought alky burning engines had to run a lot richer because of alchohols higher stoichiometric ratio?

Just some info on EGR valves. There are 2 different kinds of EGR valves. Positive back pressure and Negative. Usually our cars come with Negative from the factory. If you look on the valve there will be a part # then a P or N after it. Most replacement valves are Positive. Positive back pressure valves wont open with just vacuum on diaphram. They also have to have a slight positive exhaust pressure. Hence they wont work on a car with very low back pressure. Negative valves open whenever vacuum is applied to the diaphram. Your car might pass without revving with a stock Negative type valve.

The reason most aftermarket valves are positive is that type of opening prevents the egr valve from opening prematurely. Thus eliminating a bog and driveability/come back problem. I myself have installed this type of valve on trucks that had problems with the egr opening prematurely. It's a great cure for that.

Also, if you're HC are not a problem, get your tune in as close to 14.7 as possible (for the cat) and then run the engine cooler with a thermostat of 170 and have the fan(s) ON. This will help reduce NOx. I passed NJ inspection without EGR (vortec heads).

All L03 engines must use a positive type valve.
With a low restriction exhaust all that is needed is a little more vacuum at the valve, This can be done by drilling out the hole where the vacuum line goes on. (just a little bit)