plz help... my 91 won't pass CA smog??

[ZZoRRa-1]

I have a 1991 ZR1 with 26k miles.
I am original owner, car sat for almost 10 years.
I drive it everyday now, put 17k on since May '02.
Car passed smog then, but won't now?

smog shop says the "NOX" are too high. everything else passed fine.
my mechanic says he doesn't have equipment at his shop to check "NOX" .

Has anyone else had problems with California smog on their corvette?

and does anyone (pleeze) have any advice for me?

ZR1SPEED@ATT.NET

 

[Jeffvette]

Simple tune up will probably work wonders. Plugs, wires and maybe even coilpacks.

Is anything else not passing on the test?

 

[Train_Engineer]

I don't have the same engine, but my '94 LT1 just passed the SF Bay area enhanced smog testing, but it also had high NOx. I suspect the EGR may be misbehaving (I have 81,000 miles on it). NOx is formed by high combustion chamber temps - might be running a little on the lean side. It does not take much for NOx to climb up. The ZR-1 engine does not have an EGR system (I believe), so maybe also with a tuneup as previously suggested, the O2 sensors should be scanned for proper operation. Might want to pick up a copy of "Corvette Fuel Injection & Electronic Engine Management" by Charles Probst. It provides a lot of info on the fuel injection system, emissions, and emission control systems. Good luck.

Tom

 

[Bakinblk]

Hib Halverson is the one to talk to in Cal about smog tests.
He also had trouble passing lately, no problems in years past.
He found they CHANGED the limits allowed, and now some cars can't pass, even when at or below their old test results.

Cal's way of getting out the old, cashing in on the new(tax&lic fee)

He did get it resolved I believe.

Good Luck.

Tim - Ex California Native, smog-free for 15 yrs:s :s

 

[Hib Halverson]

It is true that CARB has been incrementally lowering the cut points for certain pollutants. The public explanation is that testing shows that most cars can meet the standards. The unofficial reason is the environmental jihadists who run our state government can drive some previously legal vehicles off the road by dropping the cut points.

Earlier comments about checking EGR is bad information. 91s don't have EGR valves.

Also, the suggestion to read the Probst book on Chevrolet Fuel Injection is a not a good one, either. I've read it...twice, in fact and I think 1) it's an absolutely rotten book full of technical errors and 2) there's very little information in it on troubleshooting vehicles that fail emissions tests. Your best reference is the Service Manual.

My 95 flunked smog last fal for the same reason, oxides of nitrogen (NoX), specifically the car failed the low speed (15mph) part of the enhanced test. 93-95 does have EGR so, at first, I couldn't figure-out why, in-spite of installation of new cats, why the car was busting the NoX limit. After two tries and two failures, through some careful road testing, I found that the OE calibration doesen't turn on EGR until 17mph. The solution was to have my cal. guy burn a new cal. that turned-on EGR at 14 mph. Then the car passed.

The above doesn't apply to a 91, unfortunately because, again, 91s don't have EGR.

I'd make sure the engine is running properly and then, if it is, you might try putting new cats on it. Unfortunately, you're looking at about 2000 bucks to do that because, on 90 and 91, to replace the cats you have to replace both the exhaust manifolds *and* the cats with 92-95 parts.

Feel free to contact me privately if you have more questions.

 

[ZZoRRa-1]

Thank you to everyone who replied regarding my "CA NoX Smog" problem.

I will let you know how it turns out...


Hib, I will be in touch (I have several questions regarding CA smog). Thank you!!