Ok- so I bought a Vette off this forum from Arizona. I live in California and knew it would be a process to get past the smog *****. When I got the car into CA, I had cats put on and took it to get smogged to see if they would notice the longtube headers. Which of course they did and dinged me on that and a lot more. The N2O system had no CARB sticker and they didn't like the Air Intake Sensor being relocated to allow the N2O to be plumbed where the sensor used to be. Also, they didn't like that the fuel pressure regulator was plumbed into the vacuum, they wanted it vented into the intake tract instead. Funny thing is, I passed the sniffer test with flying colors. They failed me on the visual only.

I spent the last month getting stock exhaust manifolds installed, disconnecting my N20, putting a stock air intake sensor back into the stock location, and taking the vacuum line off of the fuel pressure regulator and venting it into the intake tract. Go back to smog, and guess what?? I passed the visual, but failed the sniffer. My NO numbers are through the roof! The car is running 5-10 degrees hotter than it was previously, and my A/F ratio guage wasn't sweeping anymore, but was static at right around 14.9. Back to the shop, found a tiny pinhole that they welded up, replumbed the vacuum line to the fuel pressure regulator (Which incidentally, made my A/F ratio guage start acting normal again. Weird huh?) Took it back to the smog to see if that fixed it, and failed again. Hooked up the intake temperature sensor back to where it was with the aftermarket relocation kit, and ran it again. It started out really low on the NO, then after it got to 15mph, it steadily changed and the readings got worse. WTF????? The car is going back into the shop tomorrow and they are going to pull the EGR system and see if the valves are bad. I have no idea what is going on here. Any ideas? Anything I can tell the shop to check that they may not have already???

Thanks in advance guys.

 

What year is the car?

 

1997 automatic, with a 3200 stall converter, LS6 intake, blawckwing, tuned

 

Probably a tune on the ECU, you'll most likely have to have the computer put back too.

 

It has likely been tuned for when it had headers and no cats. Have it tuned to stock California settings and see if that improves things.

 

have you considered moving? South Carolina is nice and we have an ocean too. I know you would pass here.

 

This thread might help:
http://forums.corvetteforum.com/nort...sing-smog.html

 

Ok guys, its not the cats, they are new and functioning fine. If the cats were bad or not hot enough some of the other numbers would be off. The real question is why did the NO numbers go through the roof after only replacing the long tubes with stock exhaust manifolds. Something must be malfunctioning. A tune can't be that sensitive. I'm thinking that there must be some form of exhaust leak or vacuum leak causing the condition. Is it possible the O2 sensors are to blame? Also, do I need to run the obd drive cycle? I ran that right after I had the cats put on and it passed with flying colors. The next change was simply to swap the headers for the stock manifolds and put a stock intake air temp sensor back in. That's all that was done to the car. Now the NO numbers are sky high. It seems like the computer is pulling fuel and making a lean condition. I just don't know why though.

 

You gave all the performance up at your expense. Now your going to pay for a retune..... You could likely have done better just buying a car that had already passed the Calif emissions...........[/QUOTE]

8Vette7- yeah this doesn't help. Keep the neener neener I would have done it right comments to yourself.

 

OK so you changed all that over and a car that should run rich due to the no cats and headers tune it had in it is failing NO. Sounds like you have a vacuum leak or maybe the FPR you vented is having issues. Not sure. But since it seems your car is running lean and creating high combustion temps causing NO failure you should look for unmetered air getting in somewhere. With your car not retuned, I would assume it would fail CO not NO putting things back to stock.

 

I agree. I dont think that the tune is the problem. I'm wondering if there could be an air leak near the O2 sensors or ahead of them, that might be causing the computer to think that it needs to pull fuel out? Maybe its sucking air in through where the O2 sensors are threaded in? It was weird because I watched the last run on the sniffer and the NO started off very low, but as time went on, the NO numbers started gradually going up, like the computer was trying to compensate for something. Tomorrow it goes back for a smoke test to try and eliminate any vacuum leaks. They are also going to pull the small lines that connect the two exhaust manifolds behind the intake manifold and see if the check valve is stuck in that or if it has carbon build up. I'm kinda at my wits end trying to figure this out. There is just no good reason that I can see for the engine to be running like that.

 

PM sent

 

This is why people pulling all the emissions stuff of their car for 5HP extra is silly. I guess it's the next guys problem after the car has been hacked up. With as hard as it seems to get through with Cali's emissions, I can't think of why anyone would take a chance on a modded car from out of state without it passing BEFORE money changed hands.

 

I realize you are relatively new on this forum and are frustrated with the problems you are having. I believe 8Vette7 is a very knowledgeable forum member and spends a lot of time trying to help members solve their problems. It would be wise on your part not to try and PO members who are giving advice. You probably just lost one source of very good help.

 

To me it sounds like when they tuned it for NO cats---they turned the entire COT system
OFF and disabled the REAR 02 sensor reporting so it won't throw any codes--
It may seem like the cats are working----but they're NOT--In order for a cat to work it has to 'light off" they actually glow red--to burn off emissions
High NOX readings are 99% of the time caused by cats that aren't lighting off---
Putting on the STOCK exhaust manifolds will make the engine actually run LEANER not richer---To make the cats light off it takes a burst of fuel when 1st started--On a car that has an Air Injector pump--it aids in richening up the PT AFR by sending outside air into your exhaust "tricking" the 02 sensors to add fuel to compensate for the lean mixture--
This brief extra fuel lights them off (why the AIR pump always comes on only
briefly when 1st started)
Is your air pump working and hooked up ???
Another way to get the cats to light off---is to SUBTRACT tons of timing in the start-up low fuel use areas---I do it all the time to help cars pass--In the hi octane spark table from 400 to 2400 RPM and from .08 to .40 grams of fuel--set all those timing values to
10*----It will light off the cats and clean up the NOX---Then after it passes have your tuner return the timin to the way it was---Pain in the butt but I have to do this all the time on highly modded cars here--especially ones with LT's or aftermarket cats--

PS: with 10* of timing it will run like crap !! untill you return the tune

 

Thanks for all of the advice guys, did the smoke test and found the vacuum leak on the pcv line that runs behind the manifold. Fabricated some new lines and it passed smog. I'll take it and have it re-tuned when the new factory lines show up. I think that I have to remove the intake manifold to install it properly? I'll have the O2 sensors checked out and at least have them look at the tune that is on the car and see what was done. I bought this car knowing that I was going to have issues getting it through smog. Those issues were worked into the purchase price of the car and I still got a heck of deal with all of the mods that were done. The NOx numbers at 15mph were very low after the new lines were rigged, but marginal at 25mph. I'll have to look into it, but it seems that unmetered air entering through a vacuum leak was the culprit. Thanks again to those that gave honest advice as I did take all of that info to the mechanics and we checked everything we could.

ATCWIZ