95blackm6

Ok everyone, I searched the forum and google before posting, so dont bash me.

I took my 95' Z28 to emissions yesterday (Colorado BTW) and it failed the HC's miserably, the limit is 1.20 GPM and Im at 19.3589 GPM. It is a dyno type test going up to 60mph. My NOx was close to the limit 2.23 vs 2.50 as well, not sure if that helps.

I have a K&N FIPK, stock MAF (which I just cleaned), 52mm Edelbrock T/B (just cleaned), aftermarket 3" cat (probably 2 years old now, but only about 15,000 miles on it) and Flowmaster Cat Back. I have not found any exhaust leaks, I have the factory manifolds and Y-Pipe, the O2's were replaced recently also. I have not tested fuel pressure or my EGR valve, but they have not been altered. I only have a thousand or so miles on the oil, the air filter is clean, the plugs looked good visually and the wires were just replaced. I have no DTC's per my Hypertech, I running the stock tune, the Hypertech is only for tire size, rev limit, top speed, etc. I have a stock T-stat and the fans are set at 180*, should I have them set higher and run the crap out of it?

So my check list is as follows, am I on the right track?

Check fuel pressure
Check FPR regulator (leaking, etc)
Confirm O2's are reading properly


Whatelse can I check? The car runs fine, it does smell rich at the tailpipes...
I also think my mileage to work, the emissions place and home was terrible (a little under 1/2 tank) but I did drive probably 110 miles in total running it pretty hard on/off, in stop-go traffic both ways, some highway and A/C the whole time...

Any suggestions on what I should do? I forgot the ECT sensor has been replaced as well... Should I put a few gallons of E85 in it and run the crap out of it? Do I Sea Foam it since it has been running rich for awhile?

Any help would be greatly appreciated! I am about to put my head through a wall.

jaycenk

iTrader: (1)

What was the engine temp at time of test? do you have fans reprogrammed for lower turn on temps? Do you have a 195 or 180 thermostat? What type of exhaust on the front end. Headers, manifolds? Do you have a tune done to the PCM? Any internal mods to the engine?
Has it ever passed this test before with 3 inch cats? Are the cats in stock locations?

95blackm6

Not sure of the engine temp, Id guess 195 or so, I have a factory replacement T-stat (is that 195*??) My Hypertech is set for 180* T-stat right now. I have factory manifolds and Y-pipe w/all emissions functions intact, no tune, im not running the engine tuning from the Hypertech. All stock internals, 120,000 miles, doesnt smoke, no codes, new Evap canister...

I believe it passed with this cat when I bought it (about 2 years ago) it is a single cat in the factory loaction right after the y-pipe merge before the cat back flange.

Does this help?

So I gather I should turn off the lower fan temp, run the crap out of it and prey it'll pass? Maybe on some E85 to lean it out some?

Ed Wright

iTrader: (1)

The factory thermostat for an LT1 is 180 degrees. Very high hydrocarbons are usually over-advanced timing (you said the tuning is stock), mis-firing, righ mixture (your CO should be high too) or weak cats. High Nox could be the EGR.
Raising the fan temps may help a little. Drive it for several miles on the highway, then straight to the smog station and hope it doesn't have to sit long. Want the cats hot. AIR pump works, right? It heats the cats also. Stock cats are better. I tested my old '95 Camaro with & without stock cat. Made exactly the same power. Absolutely no reason to change cats with a stock engine. Stock cats sure do a better job of cleaning up the exhaust.

95blackm6

Thanks Ed, I didnt change the cat, the PO had it put in to pass emissions... the car had no cat when he bought it. The air pump does cycle on key, but ive been told it doesnt run much after initial start-up. My NOx was pretty close to the limit, do you think my EGR valve is failing/sticking? Do I remove it and clean it?

Any tips to get it to pass with this cat? I dont want to replace it until I go to long tubes w/dual cats...

Ed Wright

iTrader: (1)

You might make sure it functions and is not full of carbon. The AIR pump only runs 240 seconds at start up. It's just there to heat the cats up faster. The hotter the cats the more efficient. That's why I suggested highway driving to warm them up just before arrival at the smog station. If they don't test it pretty soon it won't help. You may need to buy cats to pass. If you could make the AIR pump run all the time the engine runs it may check cleaner. I never tried it, just guessing. They might notice that. Not sure about that either.

95blackm6

Thank you very much, I appreciate the help/suggestions, ill see what I can do.