OK, this is driving me NUTS. I've failed emissions already 3 times and today a fourth. I'm in Ontario Canada and we don't have visual. I've got L03 with 140K, edelbrock tbi intake, open element. I was failing all aspects and so I changed the o2 sensor and brought that in line. Nox was still too high. The mechanic suggested perhaps a bad cat. Well, I just installed hedman hedders(wo AIR, I welded in a bung for the o2), new Goderich SS swirl cat and magnaflow 3" ss catback. Reset timing to 0, put my stock chip back in and the Nox is throught the roof!! Limit is 633(I think) and it read about 1900!! What the hell?? I'm at my wits end here, I don't know what else to check. I checked the EGR which seems fine, pressed on the diaphragm and it wanted to stall, released and all was well. I've decided to pay the $99 and have the 'diagnostic' run on it to see what's wrong. Why not, I haven't been ripped off yet this week lol! Any suggestings?? I'll post results if/when they become available.

OK, now they're telling me that the EGR valve IS only functioning one way. The backpressure is non existent and perhaps that's what's causing the very high Nox readings. They're going to try a one way EGR from the early 90's to see if that works...

I had that problem also after putin a new engine and everything else it my car high nox comes from higher than normal temps during combustion. I reassembled the tpi more carefully to stop any air leaks and it passed with no problems a

Sure but what causes the high temps?? From what I understand it's the EGR and these cars have a 2-way EGR, vacuum and backpressure and apparently I'm not getting the backpressure force for the diaphragm to work properly on the EGR.

gt500pwr vbmenu_register("postmenu_3009808", true); - It wouldn't hurt to pick up a can of SEAFOAM liquid from Autozone, if you have them up there. Follow the directions for running this through the intake manifold. With 140K and EGR issues, you can bet you built up a bit of carbon inside the engine. The SEAFOAM when used as directed will disolve the carbon and basically flush it from the engine in a huge smoke cloud. It will smoke out the tail pipe for about 15 minutes and that's normal. You may want to repeat to really clean it good. I have the same block but mine is a TPI setup and my EGR crapped out and really blacken the intake, throttle body so bad that some vacuum ports were totally plugged with carbon. My car never had a chance of passing emissions. Even after the mechanics are done, run SEAFOAM through it.

That crap in a can (seafoam) doesn't dissolve the carbon in the chamber, it'll do the same thing as plain old water for far more money. The smoke you see from the seafoam is the junk that's in it burning up in the combustion chamber. If you want the same effect, use tranny fluid, it'll do the same job and give you the 'neat' effect.

Any codes? How's your timing? Overall running temp?

What the hell are they talking about a plurality of your egr? It is one type or the other. Find out which is the proper one for your car. Verify you have it and that it is working. And how hot are you when going into these places? What type of test are they doing?

Are you waiting to hit operating temps or are you running it only between your place and the test facility? Make sure you run it good and long before you bring it in, particularly without those air tubes. You need to give the cat some extra time to heat up really well. How's your timing?

Does the cat have an air tube and if so is it connected to a working air pump? How's the state of tune? Fresh oil change? What were the other numbers? How's your timing?

How's your timing, check the temp of your stat, make sure your pcv valve is the correct one and functioning properly and... Run through this:

(Thanks Vader)


Did I mention the timing thing yet?

also depending on how much room you have on other areas of the emissions testing you might be able to semi cheat it if you retard the timing a bit from stock though that will increase COx emissions. or maybe trying to squirt a very small small amount of water into the intake if you can find a small enough restrictor. but these if they will work still don't fix the problem instead just mask it.

why did you buy headers w/o air tubes?

the type of EGR valve used on your car can be had in 3 types, positive back pressure, negative back pressure, & a non-back pressure valve.
the back pressure valves have a letter on them right after the part number, P for positive & N for negative, no letter means its a non back pressure valve as far as OEM goes.
some of the back pressure type valves are sensitive enough that just changing the muffler to one that has a different amount of restriction can cause it to not work properly.

the design of the motor has a lot to do with NOx production, ignition timing too high will cause igh NOx numbers as will combustion chamber deposits.
on a stock motor like the first generation small block chevy a properly working EGR system is mandatory to lower NOx. the cat is the last part of NOx reduction. a lot of after market cats don't do much for NOx.
engine temp has less to do with NOx production than most people think, on a properly running motor without heavy combustion chamber deposits, from dead cold up to the point just before over heating makes only a small change in NOx. its the combustion chamber temps that cause high levels of NOx, 2500 degrees & higher are where most of the NOx comes from.

All this is great info guys, I love this board. Anyways to answer some questions. I reset the timing back to tdc, maybe 2-4 degree advance. I removed the smog system long ago which is why I have hedders without the air tubes. There's no visual here anymore so I scrapped it, makes a real mess of the engine bay. Also, the EGR from what the mech said was a negative backpressure type and the exhaust system was not allowing it to function properly, probably causing the high nox. The engine stays nice and cool, new stat last year and cts. They're gonna try a non-backpressure style to see if that passes the nox. Unfortunately that may raise the hc's above the limit. Oil change was also done just prior to the test, royal purple and a new fram filter. I won't get in there again until next week though, I'll let you know what happens.

The problem is a simple fix.
Where the vacuum line goes on the valve, you need to drill out the hole a few thousands. But make sure you use a wire drill about .025- .038. Too big and it will cause a bog when taking off. What this does is add a tad more vacuum to help open the valve when you remove the back pressure the stock exhaust had.

When I have done this it will drop the NOX from 1300 down to 400.
HTH

High temps come from a lean running engine. the temp on your gauge can be normal and still have high combustion temps. the egr just lets some exhaust in to cool things down. I'd buy one from a GM dealer you would be pretty shure that you have the right one.

I agree.... GM only...but you still need to drill it with headers and catback exhaust.

I am running hollowed out cats, and dummy tubes comming off of headers to pass the visual. I found that running E85 5 gallons with 2 gallons of 85 octate, changing timing to run as smooth as possible. The engine will run a little rough but should pass emissions. I have TPI but in theory should work with TBI. E85 should not be used all the time for it will eat through the rubber gaskets. If the check engine light comes on it will be because the car is running too lean so I needed to richen the air fuel ratio by adjusting the idle. Make sure to reset to stock when done.

Drilled out the EGR to 292 #69 drill and nox went UP!

Does anyone know who makes a non-backpressure style EGR for this application? That should do it.