Hi everyone,

OK, I've had an emissions test run on this car twice and both times the results are virtually the same. Here's what the car registered:

TEST 1, Aug 18 2005
HC limit: 58ppm, actual: 36ppm - PASS
CO% limit: .32, actual: .01 - PASS
NOx limit: 652ppm, actual 1078ppm - FAIL

TEST 2, Aug 24 2005
HC Limit: 58ppm, Actual: 38ppm - PASS
CO% Limit: .32, Actual: .02 - PASS
NOx Limit: 652ppm, Actual: 1084ppm - FAIL

As you can see, the numbers from both test are virtually the same and both times the car failed on NOx. I should mention, the second test was done after I had run a bottle of that "Guaranteed To Pass" stuff through a full tank of fuel. Obviously, that did nothing.

From what the tech told me, it's either: the EGR isn't working, there's a lean condition (ie. bad O2, vacuum leak, or exhaust leak), bad catalytic converters, or excessive timing advance. i have noticed that the car is running a little (by only about 4 of 5 degrees or so) hotter than it used it. No codes are stored, so I'm going through the process of narrowing down what the problem might be. Here's what I've done so far:

The tech said that if all I want is to get the car to pass, just set the timing down to 0deg, and it'll pass easily. But that doesn't ultimately solve the problem. If my car has a mechanical failure somewhere that's ultimately causing this then I want to fix it. I do know that the O2 sensor was changed about five years ago or so.

I don't know if what I'm doing is right or if I'm just wasting my time. Can someone help guide me in the right direction?

 

I was going to explain how the NOx was a byproduct of high combustion temps and that the EGR valve is what lowers the combustion temps. The fact that you can't pull a vacuum on the EGR valve, demonstrates that the diaphragm in the EGR is shot. You have found your own problem.

RACE ON!!!

 

I agree.Replace the EGR and it will drop down Nox big time.You need less than 220 ppm to pass up there?

 

Hi guys, thanks for the responses.

I agree that NOx is a by-product of high combustion temps, which would expain at least to a certain degree why the car is running a little on the hot-side, and why the car failed emissions (obviously).

I can change out the EGR pretty easy - maybe an hour's worth of work. But is that it? Just, pull a vaccum and if no movement, Re&Re? End of story? I've never fixed ANYTHING on this car THAT easy!

I guess I'm just having trouble believing that I've actually found the problem so quickly.

The EGR is a pricey piece up here in Canada (dealer price is almost $200, and aftermarket is around $100). Do you guys think it's worthwhile to try a used unit, or just shell-out the cash and get a new one? I'm sure there are lots of people on the C4 Parts for Sale/Wanted section that have their old EGRs lying around and that they would send me if I covered the shipping, but I don't want to waste my time if a used one is no better than the one I already have.

Thanks again for the responses guys.

 

Yeah.

When you think of it, it's kinda dumb that they wouldn't just give me a conditional pass too! I mean, the tech looked over my car and couldn't believe that it didn't pass. Heck, even bystanders were like, "DUDE! Your car is mint, what do you mean it didn't pass?!?" He kept reassuring me that at such a small amount of NOx over the limit that my car wasn't a polluter. I turned and told the guy, "I'd put my car's emissions results up against any of today's high-performance cars - import or domestic! I know my car isn't a polluter, but it obviously has a problem and I want to fix it!".

But hey, if changing out the EGR will give me the pass, then so be it. There's not much good-weather left this year so I figure if I can get to drive it 'till at least the end of October, then it'll be worth the cost and effort.

 

Also check the EGR vacuum switch and line located under the throttle body

By all means get new egr valve..$100 is okay

As you mentioned, there are no easy jobs on the vette (the altenator is the exception). Go to one of those tool store and pick up a set of off-set wrenches. The EGR valve bolts is difficult to get to.
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Wanted to ask something,does your car ever run a bit rough or stall?I was just curious even though you threw no codes.

For those that dont know,Yes a sticking or faulty egr can cause that sometimes.However if the diaphragm wont move up and down on vacuum and stays in one place,then it can cause higher nox and pinging in some cars.

With older cars,sometimes I would check the egr diaphragm with my fingers to push it up and down,to see if it was binding or stuck in one place.
With the L98,thats not really possible since its in the middle under the plenum.

With the egr off the car,see if its clogged with carbon as well.If the intake holes for the egr passage is blocked,scrape it loose and use a shop vacuum at the same time to get crud out of there.

These are just general tips for anyone to try if theyre going to check,repair or replace the egr.