I'm still struggling to pass Tennessee Metro emmissions with the new modified motor in my 89 TPI car, it has the Vette aluminum heads and no EGR. To get it running, I deleted the Cat and ran the exhaust from the SLP headers into the new 3" Edelbrock CAT back system. To test emmisions, I put on a brand new Magnaflow Car Sound 3" CAT.
My question to all of you is- have any of you added a new CAT to a system that has been run without a CAT and then tested for emmisions? I'm afraid that the Edelbrock muffler has residual HC contamination, and I'll need to do something with it before I can pass. My car is no where near stock, so I think it was running pretty rich(I've tuned it up). I don't think my car compares to a stock car with a worn out CAT. Please let me know your experiences- thanks.

 

Do you have the air pump?

 

I took the air pump off, also removed the EGR (I've got the corvette alum heads), and I've got a big cam. I know this could be a most of the problem. However, just for a check, after I failed last time, I took the new converter off and retested. HC went up, but it wasn't nearly as much as I thought it would. I'm worried that if I put in a different cam, or add back some of the emissions stuff I may also need to replace the muffler because it is probably saturated with HC emissions.
The reason I posted this is because I was wondering if anyone out there runs most of the time without a CAT, and then is successful testing when they put one on. Thanks

 

The Cat doesn't do much without the air, so that could be the problem.

The air burns the hydrocarbons in the Cat, without air you only have a little oxygen left in the exhaust to work, if you burn lean, if you burn rich, there is no oxygen so the cat does nothing.

The EGR is to reduce nitrogen oxide in the exhaust, by cooling the combustion. so if you don't have high NO the egr wont have much affect on the emmissions.

 

dont corvettes use an external egr system.. so they can past emissions..

 

Having lived in TN, I can tell you the EGR has nothing to do with the emissions they check (HC and CO, they don't check NOx).

Put your AIR back on, that should clean it up. I used to run a 400 with a Comp XR282HR and a Holley 800 through that, it would pass squeaky clean with a good cat and the AIR on it. I usually just left the AIR hooked straight up to the headers, did away with the big valve thing and plugged the line going to the cat, since I didn't have the computer to control the valve anyway...

Never heard of "residual HC". That would basically be unburned fuel hanging around in the exhaust. Not bloody likely.

 

Thanks for the suggestion on the AIR pump. It makes sense that putting extra oxygen in the converter will help it light off and further dilute the exhaust to lower HC concentration.
I've got a question on how you hooked it up, couldn't quite understand your explanation. Did you run it to the individual exhaust ports like factory, or did you just run it back to in front of the CAT? I think you would need the one way valve, no matter what. I'm trying to stay away from the individual tubes, it looks messy & makes it harder to work on the engine. I welded an extra O2 bung just in front of the CAT before I sent the headers off to be coated, just in case I wanted a sensor for real time monitor of the exhaust. I'm thinking about plumbing the output from the AIR pump into it.
Also- what CAT did you use on your 400? I think I'm going to need something besides a high flow CAT, maybe something off a regular production vehicle. I'm really not worried about flow anymore, I just want a set up that will pass. Thanks

 

I had headers with the tubes, so I just hooked a couple of pieces of heater hose and a T to the check valves that feed the tubes to the headers. I blocked the cat air line off.

The stock computer-controlled setup only sends air to the headers while it's in open loop; once it reaches operating temp and goes into closed-loop, all the air goes to the cat.

I've had several cats on it over the years; the stock L69 one, a Catco with flanges from SLP welded on it, etc. They all seemed to work fine as far as emissions were concerned.

 

Thanks for the reply. I think I'll try running the pump output right to the CAT. I rewired everything in the engine compartment, so it would take some time to wire the solenoid back into the ECM. I will only test when I'm fully warmed up & in closed loop anyway. I'll just plumb it so the air pump is always flowing into the CAT. Thanks much for the advice.

 

You might be safest with the air only to the cat, because the air and unburnt hydrocarbons do burn and that burning rather than dilution is what brings down the HC in the exhaust.

If you do that in the headers you could melt the steel real easy at high throttle settings. Blown air and hot steel will corrode the headers fast.

The Cat is designed to burn the traces of HC at lower temperatures - although still very hot - without melting the exhaust system.

Because of the temperatures involved, the connection to the Cat must be silicon tube. Also you need the anti blow back valves in line.

Be nice to the tester, because in some counties in some states, the inspections include checking everything is original.

 

Yeah - I second that running it straight to the CAT. Mine's like that, and I passed no problems - and they check NOX too here.

 

Update on the emmisions test- I finally passed. I put a new "cheap" Arvin Cat (3" in & out) on & hooked the air pump directly into it. The after I first put it on, I was concerned because the CAT didn't seem hot enough. I've got a thermocouple for my dmm & hooked it to the CAT body - it was only getting up to about 250 deg F max. I thought this was too cold (i've got an Edelbrock CAT back 3" system) & thought there wasn't enough back pressure to heat the CAT, so I welded a plate in back of the CAT and only put a 11/8" hole in it. I was able to get up to 350 deg on the CAT so I tested with this set up and failed (321 HC 220 ppm test limit). I removed the restrictor and tested again and passed (191 HC ppm). I think the restrictor created too much backpressure and the air pump wouldn't put enough air volume in the CAT at idle- taking it out lowered the back pressure. But--------- when I tested it was cool and rainy, I'm worried about passing next year becuase it was so close to failing this year this year. I'm thinking about getting an LTI cam in place of the big Comp Cams stick I've got (224/218- real lumpy idle). Any comments would be appreciated. Thanks

 

I don't know what temperature the Cat should be at, but the catalyst allows cool burning and clearly it was OK.

I would start worrying about next year's test next year. The HC could be oil or gas, and the gas could simply be a hot cam, allowing more overlap and that releases more air and gas to come out with the burn exhaust. Basically when the inlet opens and the exhaust is open, some of the inlet goes straight out the outlet. My guess is that's why you are close to the limit.

 

I have my air pump going straight to my CAT also. I think the only downside to it, is that it the CAT doesn't heat up as quickly - but that's no big deal. You should always take your car to Emissions Testing with the engine at full operating temp.

I've passed 2 years in a row, no probs. HC is unburned fuel. you're running rich. Did you replace the oxygen sensor yet?? Do you get any codes on the computer?

 

Mike,

I just bought a Trans Am with no cat and it failed emissions miserabley here in phx. I had a cat installed and the air pump rehooked up and it pass with flying colors. However I don't have the mods you have. I have an after market cam but it is very mild.

One more thing.....

GO VOLS!!!!!