I took the vette to get etested tonight and I failed horribly.

I had the two speed idle tailpipe emission test done. I passed the 2500rpm test and failed the idle rpm test due to high hydrocarbons. 650ppm vs 150ppm limit.

Complete Results.

2500 RPM IDLE RPM
Reading (Limit) Reading (Limit)
HC PPM 51(150) PASS 650(150) FAIL
CO% .11(.7) PASS .25(.75) PASS
NO PPM N/A N/A
RPM 2313 VALID 876 VALID
Dilution 13.4 VALID 11.6 (VALID)

Is there an gas additive that will give me a chance as passing? Is it a cat issue? Wouldn't a cat issue fail the 2500 rpm as well?

NOTE - These results were done when the car was fairly cold. I live literally 1 min away from the drive clean station... I started the car, basically 1-2 gear speed until I got to the station. The car sat for 30 minutes cold. The car was then started and warmed up for about 5 minutes before the start of the test. Is 5 minutes at idle or low rpm enough to heat up the high flow cats?

The car has a built LS6 with blower cam, a 112 maggie on top with long tube headers and high flow cats.

You can definitely tell the car is running a bit rich as you can smell it.

Any help would be appreciated.

 

Blower cam is not helping. Has the car been dyno tuned and AF levels optimized?

 

Yes. I bought the car last week and had it shipped up.

21st Century Musclecars tuned the car a week ago.. both dyno and driving.

If the car is still "warming it" will it run that much richer? Could the car be tuned to dump more fuel at idle when its cold?

 

I'd start with the tune as well. Get it checked and go from there.

 

The car should regulate to 14.7 to 1 a/f once its up to temperature. I'm going to test it by getting a temporary permit for it and running the snot out of it for 30 minutes then hook it up directly to the clean station.

 

Yes...I was told by a smog station down here in Cali that you want to run your car for at least 20 minutes or so before bringing it in to get the cats warmed up. Then they are working at full potential.

 

Could an exhaust leak before or after the cats be causing this?

I just had my wife start the car and noticed exhaust hitting the cold air right after the longtubes before or after the cats.

I sat in the car for a few minutes trying to listen for anything and noticed the smell was coming into the car. Gotta check it out more tomorrow.

 

You need to have the car at NORMAL OPERATING TEMP.......not cold or just warming up.......It was probable running rich. Warm the car up.....
cold cars normally run rich, this is why on old carborated cars the butterfly would be halfway closed in the carborator while the car was warming up......Your emissions tester should have known that, common sense...

 

Ditto the warm-up remarks. You can't e-test a car when it's cold. I've had trucks pass with almost 300kkm on them and pass with flying colors. I always take a vehicle in hot just in time for the test. The shop should make sure it's up to operating temp before doing the test. If you have a leak in the system prior to the cats then it may be that the O2 sensors will read incorrectly and over fuel to compensate.

If you aren't up to temp then you're likely still in open loop mode until the O2 sensors get going. That coupled with the cam (rough idle?) will throw off the idle numbers.

 

I am running long tubes with 3" high flow cats. Are your cats in front of the X pipe or behind. I initially installed the high flow behind the X pipe (supposed to be better for TQ) and almost failed (but it did pass) but the cats were running way too cool. I moved them to right off the collector to get the heat up and they passed the next time no problems. The car was WELL warmed up. No need for speed, just run down the road in a lower gear at higher RPMs for a few seconds.



If you have anything off serious you would be throw~n codes. Are the rear 02s hooked up, do you know?

I use HP tunner software with several different set-ups. One I throw in a couple of days before the trip to the smog station, couple of days of driving gives the tables time to update.

 

Fresh fuel,,fresh oil can help too,,,then have the motor WELL warmed up. In an extreme case,,run some regular gas in it. Regular burns much quicker(that's why it will knock if you drive hard,,burns too fast ='s knock) and should help on the idle test. Now I'm not talking a tank full ,,just run the tank down a bit and add a 1/4 tank,,and run around for a while and get it good and warm,just don't push the car hard. Sounds like the cats were not hot enough to work at idle,,2,500 gets them warmer. Long tubes put the cats a little to far to get a good "quick light off". IF the cats are good,,getting them good and hot will help.

 

I have to admit when I first saw this thread, I thought the post came from California. Here in Cali, before I go to the smog place, I do a nice 30 minute jaunt down the freeway which seems to get me to pass.

 

and I would add that if you're running a cam and long tubes, the engine has GOT to be warmed up completely (freeway best) and the use of regular gas are both a must.

 

List of mods:

Supercharged 2004 Chevrolet Corvette Z06
Millennium Yellow Exterior/ Black Interior
600 Horsepower Horsepower 521 RWHP
Polished Magnacharger MP 112
Custom Lingenfelter Fuel Rail Covers
Lingenfelter Forged LS6 installed at 46,800 miles
21CMC Camshaft Package, Blower camshaft 224/228
LG Motorsports Pro Long Tube Headers W/ cats & X
Patriot Dual Valve Springs
ACI High Rise Hood, professionally painted
Ported 90mm Throttle Body
WCC Hurricane CAI
Magnuson HD Belt Tensioner
160 Thermostat
Corsa Indy Pace Car Exhaust w/ Pro Tips
GM LS7 Clutch/ Flywheel/Master Cylinder/Slave Cylinder
with less than 2k miles
New Baer Rotors 2pc Front / 1pc Rear New GM Brake Pads and Stainless Steel lines / Motul Fluid
GM Seat Covers Replaced
Taylor Spark Plug Wires
NGK V-power Spark Plugs
New Belts, Harmonic Balancer
ALL FLUIDS serviced regularly,including oil change and
clutch fluid every 2500 miles
Red Line Trans Flush, Red Line Differential Flush, Radiator Flush,
Red Line Power Steering Flush
15% Tint Side windows and 20% Rear Lifetime Warranty Tint Material
Front and Rear Corvette vinyl letter emblem
Custom Billet Polished Z06 Fender emblems
Billet Z06 Rear Chrome License plate
Black Shorty Antenna
Breathless Performance Short Throw Shifter W new Factory Shift ****
LPE/Lloyd Custom Floor Mats
Car lowered 1.0 inches by 21CMC
4 Wheel Wheel ALIGNMENT done by RUF Auto Centre

I have a visible exhaust leak that I confirmed tonight. Going to throw it in the air and take a look this weekend.
I am definately going to run cheap gas + warm engine before the next test after I fix the leak. I'm also going to pull the plugs to see if they are misfiring.

The car was just tuned before I took delivery.... so i'm wondering if after I fix the exhaust leak if I'll have to have the car retuned again if its due to an exhaust leak (the car would be running very rich if it was tuned while there was a leak before the o2 sensor... arg!

 

You can also try adding isopropyl alcohol to the fuel but you'll need to be careful how much. I don't know myself, so you'll need to do a search.

By the way, with the 160 T-stat engine warm-up is even more crucial....

 

Definately check and see where the cats are located in relation to the X pipe. LG origionally recommended that the cats be mounted behind the X pipe. This is god for TQ and HP but they run too cool back there and should be moved up to pass SMOG. I also have the exact same system you have.

 

Will definitely do that.

Do the fuel additives you can buy that guarantee a emissions test pass work at all?

Someone said to run low octane gas as it burns quicker... but I've also read sunoco 94 is good due to 10% ethanol.

 

Go buy a tank of the highers octane you can find, sunoco 94 would be great. Then drive your car for an hour before you go re-test


my guess the engine and O2 sensors was to cold

 

Why are you suggesting highest octane? I've never heard anyone suggest this. Lower octane burns easier, which is what you want in this situation. Just about all of the fuels are containing ethanol so I don't think it has to be 94 octane.

High quality, yes, but High Octane I don't get.

 

An exhaust leak can cause it to dump fuel. Exhaust leaks will suck outside air and the O2 sensors read it as too lean and add more fuel.

Also as stated drive the car 30 -40 miles prior to testing. Don't know if the octane make a diff.