They have been doing smog test in So Cal for about 30 years and I have never had a car fail. Until now. My 91 has failed twice. I posted a couple of weeks ago about being a D.S. http://forums.corvetteforum.com/show....php?t=1721285

and leaving the tube that runs from smog pump to smog valve after I failed the 1st time. Then it was the vapor canister filling the line to the purge valve with charcoal.

http://forums.corvetteforum.com/show....php?t=1709190.

The line from the canister was full again so I started looking for a reason and I found it. Both top and bottom of the canister has a foam insert. The foam on the bottom had lost some of the material and every time it would purge, it would suck the charcoal bits right through the foam.

I figured between fixing those 2 and changing the plugs (cut back 5's) I would pass with flying colors - wrong! Below is a scan of both the tests.



What I don't understand is the radical differences, especially in CO & NOx. Almost double what they were 2 weeks ago.
I was told by the tech that the NOx is usually raised by the temps in the combustion chamber. Since I had Delco FR5LS (out of the box) on the 2nd and now 5's that are cut back, could the temps go up that much to almost double at 15 mph and triple at 25 mph?

I could sure use some help here if anybody has ideas. This year I have had more "challenges" and spent more money on this car than I have in the past 5 years.

Thanks in advance
Subman

 

wow. same station? makes me wonder about their equipment...

What is the history of the cat(s)?

 

Dont think your plugs have anything to do with it..

Is your EGR and cats functioning properly?

 

Same station passed the Suburban 20 minutes after the Vette failed.

About 4 1/2 - 5 years ago I gutted the precats and replaced the main cat with an after market (same as OEM) so I make sure the car has been running for a while before I take it in. Today I jumped on the freeway, drove upwards of 10-12 miles, turned around and drove directly to the test site. They had the car on the dyno in less than 10 minutes.

We'll keep on keepin' on.
Subman

 

I didnt have inspections,but I replaced the hoses,metal line and the cannister itself to stop a bad gas tank pressure build up I had.

When I removed the cannister,there was charcoal in everything.You may need to replace it and be sure the lines,hoses and etc are clean of it.
Then,when it works again,it should be allright.

 

Bill - I pulled the lines, canister and valve, replaced the foam filter, blew out all the lines cleaned and checked the purge valve and then checked it eery day since last Monday. No charcoal bits, and it seems to be working.
Cruisin - I had replaced the EGR valve in Nov 05. It was alos one of the things I checked when the car was down for electrical gremlins. Stays open under vacuum and closes when I release the vacuum. See prev. post on cats
Thanks for the replys guys
Subman

 

Here's my test from the other day.



I'm ready to re-test Monday with a new cap, rotor, AC delco 41-629 plugs (for aluminum heads), and new wires. Never failed analyser before. My old wires were bad too. I always do a basic tune up before going in, but this time I just got lazy and didn't. I had a slight miss due to bad plug wires.

You high HC reading is basically incomplete combustion. Unburn fuel is being dumped out the exhaust as a result. Have you done a basic tune up?

 

My 86 VW had this same problem. I retarded the timing 4 degrees and added isopropl alchol to the a low tank of fuel. Bang! Passed with flying colors!

Something to consider.....

 

How do you get away with your set timing? Here, they want it at the factory 6 degrees.

 

Damn if you would had a few more CO on the 25mph test, you'd have a perfect score!

Shops I've talked to says within 2 deg of spec is ok, so time it to 4 deg. The dry gas is another quick fix. I'd do those two things and get your cert, then go back home and figure out what's wrong.

It might be time to replace those garbage Multec injectors. Just sitting on a shelf wears them out. If one is pissing (literally) into one cylinder, the 02 sensors will lean out the others, giving you high HC, CO, and NOx.

 

86 - I had already replaced the cap, rotor & plug wire - just held put to long to put in the plugs. I had the dist. out and put it back in at 6*

Jr. - I've been around a RELLY long time and alcohol to the gas tank is one I'd never heard before. If I can retard the timing a degree or 2, I'll try it, but like 86 said - here on the left coast they have been gettin real bitchy about factory specs and smog.

CentralCoaster-replaced the Multitecs 2 1/2 years ago. Running with the pink tops and they have worked out great. (so far)

Thanks for the replys -
Subman -

 

It seems like you have a leaky injector, because you have way to much fuel at idle, it clears up at rpm. You could also have a weak cat.

 

To all that replied -
Thanks!!
I have some work cut out for me.
We are headed out of town with the Vette come Thursday AM for my neices wedding on Friday, back on Sat evening and autocross on Sunday 7:00 AM.
Will post back what I find.
Subman