Question: 1990 L98: Failed California SMOG gold shield NOx tests

[AV8R]

Update

So far the following have been replaced:
- EGR negative pressure
- Solenoid
- 3 MagnaFlow cats

The following were tested as good;
- vacuum lines
- ECM pulse modulation
- solenoid turns on at correct times with car on dynamo
- sufficient engine vacuum

and still the SMOG test fail with hi NOx... until a rag is put into the tail pipe, which gives the EGR enough back pressure to open up as expected.
When the EGR works, the NOx is low as it should be (which means the Cats are doing their job).

What is now suspect are the mufflers or perhaps the Cats aren't restrictive enough to allow the EGR valve to work properly.

Does anyone know if the MagnaFlow cats I referenced are correct replacements for the OEM ones?

Regarding mufflers:
- what is the correct part numbers or where can I find OEM ones?
- how do you know if a muffler isn't generating the proper restriction for the 90 vette's system for CA specs?

 

[Hib Halverson]

So far the following have been replaced:
- EGR negative pressure
- Solenoid
- 3 MagnaFlow cats

The following were tested as good;
- vacuum lines
- ECM pulse modulation
- solenoid turns on at correct times with car on dynamo
- sufficient engine vacuum

and still the SMOG test fail with hi NOx... until a rag is put into the tail pipe, which gives the EGR enough back pressure to open up as expected.

How did you determine that?

When the EGR works, the NOx is low as it should be (which means the Cats are doing their job). What is now suspect are the mufflers or perhaps the Cats aren't restrictive enough to allow the EGR valve to work properly.

Because you have both the pup cats and the main cat in place, that's really hard to believe, because...pup cats are restrictive to the point of robbing power. You loose about 5hp due to the pups.

There are tons of L98s running around pupless and with low restriction exhaust systems, some even have muffler eliminators, so it's hard for me to believe, that because of low exhaust restriction, the EGR valve won't work, but if that's true; simply make yourself a couple of exhaust restrictors and install them for the Smog Check. Or, put the stock y-pipe and mufflers back on.

Does anyone know if the MagnaFlow cats I referenced are correct replacements for the OEM ones?

Those MagnaFlow PNs are the correct ones for MagnaFlow's universal fit cats (ie: dual pup cats and single main cat) for a 90 Corvette w. L98 engine. Also, universal fit simply menas they have to be welded in place rather than being a "direct fit" where they bolt in place of the originals.

Regarding mufflers:
- what is the correct part numbers or where can I find OEM ones?

You won't find OEM mufflers for a 90. You may find aftermarket, OE replacements or reproductions. Check with a Vette parts vendor like Zip Products. Zip sells PN EX-477 which are OE type mufflers for a 90.

- how do you know if a muffler isn't generating the proper restriction for the 90 vette's system for CA specs?

You may find a back pressure test procedure in the factory service manual.

Now, another smog related issue. Farther back in this thread, someone posted...

By the way, my other vet is a 1974 triple black I bought in Tonawanda right after graduation back in 1982. "Go in debt and buy a vette" was my mantra back then. It has no California smog hardware and doesn't need any. The 2005 law states 1975 and older dont require smog, but no longer do we have a rolling 30 year window to exempt aging vehicles.

Understand that the law does not exempt '66-'75 vehicles from the smog check, it only exempts them from the biennial inspection. You still have to pass the Smog Check if you sell the car in California. Also, you are not exempt if you get caught in a roadside test. If you flunk that, the only way you can solve that problem is doing whatever is necessary to pass the Smog Check, again.

Finally, you mentioned you're Chino Hills. If you get to the point that you'd like to get "another set of eyes" to look at the problem, my emission test expert is in nearby Pomona. The shop is Quality Auto Service. It's run by Mike Garabay, one of the better diagnosticians in the west end of the IE. Garabay, is, also, a consultant to BAR on writing the examinations which technicians who have smog test licenses must take to get that license. In short, the guy knows the Smog Check inside-and-out and how to get cars to pass it.

Quality Auto Service, 460 Falcon St., Pomona CA 91767 909-596-5502. If you go over there, tell Mike I sent you in.

 

[AV8R]

@HIB,

You're talking to someone that does not work on cars, so your technical questions are better directed to someone that would know how to answer them. If you want to discuss computers or electronic design automation and design, Im your guy; but Im dealing with a sick vette and Im trying to get it fixed without being ripped off (like I already have been). I also got ripped off at a corvette specialists up the road from us in San Dimas. Im so tired of this, which is why I come here to find helps.

That being said, I appreciate your responses none the less. The local mechanic reference is something I think I may take you up on if my current mechanic over his head. Finding both honest and corvette knowledgeable mechanics are as rare as finding a good doctor who won't just throw pills at you to deal with symptoms rather than the cause.

Thanks and cheers

 

[roger longman]

Quality Auto, is at 3460 Falcon st........Roger.

 

[AV8R]

What I should have done, was listen to my wife and sold this little 90 gem back a few years ago when it was healthier and could get some money out of it.
But no... I'm a stubborn and loyal corvette fanboy who would probably go broke before selling his chariot he has driven with glee for almost 2 decades.
I expect expert mechanics who are BAR/BBB/AAA blessed, to find the problem directly rather than by replacing parts until the problem goes away. How naive of me.
If we in engineering ran our business like this, we would be out of business in short order. Most folks can't even stand talking to support with an accent in my world.

So bear with me when I sound a bit gruff as I go thru these expensive and complex vette adventures. They might be minor for mechanical wizards, but for
computer geeks this is as frustrating for me, as debugging a computer software, bios, hardware and malware is for many of you. To me, those are childs play.
Getting support from other vette stricken buds who's combined knowledge base should assist folks like me, is part of what makes forums like this worth while.

Thanks for the references. Maybe a "vetted" mechanics list by state or city would be of great value to this forum.

ad

 

[AV8R]

update Feb 8th

So the saga continues...

1. It appears that neither the MagnaFlow or the CatCo cats provide the amount of restriction that the OEM ones did.
Unfortunately even ZIP doesn't have a cat that meets CA requirements.

2. We contacted the reference that Hibb provided and they confirmed that they saw the same kind of problem with this emission system and model.
They never did find a solution either, and without the OEM cats and muffler its not going to be easy to get the necessary back pressure to activate the EGR.

3. I submitted a BAR case to try to recover the money from the mechanic that took out my OEM cats and put in truck Magnaflow cats. The case is pending.
In talking to this BAR agent, he said that over the years he has never seen a 90 vette with this problem but has seen the lack of restriction being related to the EGR not working.
He also didn't have a problem with restriction being added as long as it is used to meet the requirements, and not to get around it. He understands that the current aftermarket
hardware is not fine tuned as the OEM ones were for the emission system.

4. We are looking for someone that knows how to put in the right amount of restriction to make the EGR work properly. Just experimenting, the rag worked fine, but the first shot
at putting in washers or something to create restriction actually increased the NOx, so there has to be the right amount to work.

5. Thanks to those of you that pvt msg me with ideas and workarounds. I hope I don't have to go there, but Im running out of options. Like how can I even sell my car if it doesn't pass?

 

[Hib Halverson]

Your car is the third 90, I've come across in the last year or so which is having trouble passing the CA Smog Check.

What creates this problem is 1) older powertrains and 2) the State of California gradually and retroactively tightening NOx emissions standards. I'm not sure if this has been done for 1990 cars but it's been done twice for 1995 models. After the second change in the standards, my 95 Coupe flunked and the only way I could fix that was have an aftermarket calibration engineer, reconfigure the EGR strategy at low vehicle speeds.

BAR and CARB will deny it but the one reason they are tightening the standards is to force old cars off the road.

If you can't pass, sadly, you're options are to either sell the car to an out-of-state buyer or scrap the vehicle...either way California sees that as another old car off the road.

As for restrictors, I'd make something up that slips in the tail pipes on a temporary basis and can hold a wad or two of real coarse steel wool.

 

[AV8R]

@Hibb,

Ive come to the same conclusion... that being the EPA-nicks are turning up the politically correct filter to generate funds and to kill older vehicles.
Im thinking that what we have in aftermarket hardware today may have met the standards in 1990, but not today. So no way to do it with normal replacement strategies.
Do we know what the CA SMOG test requirements were back in 1990 versus today?

Ill probably have to take my car back from my mechanic who is as straight as they come, before I can get a smog test with a temp restrictor as you recommend.
This is a very expensive process of learning and I really would hate to see my vette go, but the liberal forces in CA are playing havoc on us "nascar bitter hanger on'ers"
It may be the case where I get a temp 2 year exemption (due to the efforts already tried) from a smog referee. Then sell this puppy with only 87K on it and otherwise is in good shape.

I don't EVEN want to hear about smogging my garage queen 74. Ill let it rot in the garage before I brick that one. This site would indicate I can get a smog exemption:
http://dmv.ca.gov/vr/smogfaq.htm
Does my vehicle qualify for a smog exemption?

Smog inspections are required unless your vehicle is:

• Hybrid
• Gasoline powered 1975 year model or older
• Diesel powered manufactured prior to 1998 or with a Gross Vehicle Weight rating (GVWR) of more than 14,000 lbs
• Electric
• Natural gas powered with a GVWR rating of more than 14,000 lbs.
• Motorcycle
• Trailer

This 1997 law that repealled the 30 year rolling no smog window, did allow for no testing for 1975 and older vehicles.
http://www.recarbco.com/technical/smog/sb42summary.html



We shall see if I can get this 1990 baby to pass somehow. I don't give up easily.

 

[JCHarper]

What a bummer on trying to get your 90 smogged. I feel your pain. I bought a '94 and stupid me didn't require the owner to provide the smog cert. Anyway it failed 3 times, test only station, failed across the board. I am in an enhanced test area btw. Finally had to put two new cats and three new 02's, the '94 has three don't ask me why. Finally passed. I did replace the aging cats with CARB approved cats. Did not replace mufflers.

I was told by the smog tech, that beginning on 2013 California will be requiring bi-annual inspections of '65 and newer cars. Plus motorcycles, I thought they already were, and diesels will be included, didn't catch model years for those though. Anyway, it just sucks, especially for those that only drive their classic auto only a few miles every year. Considering how few of those years, 30 plus years old, there really are anymore. How much pollution do they really create anyway? I can see a lot of folks getting addresses in AZ just to avoid all the hassle and expense of Ca. registration .... or a lot of non-registered.

 

[AV8R]

...Finally passed. I did replace the aging cats with CARB approved cats. Did not replace mufflers...

Can you give me exact part number and make of the CARB cats you bought please?
Contact info of where to get them would be for extra credit.

I believe the cats I tried from Magnaflow were CARB, see links I provided earlier.



Ps , you referring to AB 2289?
If so, in 1/1/2013 vehicles with ODBII that are 2000 and newer won't require tail pipe smog tests, rather it will be off the computer and visual.
Im not sure what that does for older vehicles, I guess it will be the same as what there is today. Not surprising they brag this will remove 800,000 old cars, which proves their intent with SMOG laws. How exactly, I'm not clear; but this should make it easier for the newer cars and continue to be trouble for us classic car owners.
reference: http://www.smogtips.com/new-smog-law-AB-2289.cfm

 

[JCHarper]

Can you give me exact part number and make of the CARB cats you bought please?
Contact info of where to get them would be for extra credit.

I believe the cats I tried from Magnaflow were CARB, see links I provided earlier.



Ps , you referring to AB 2289?
If so, in 1/1/2013 vehicles with ODBII that are 2000 and newer won't require tail pipe smog tests, rather it will be off the computer and visual.
Im not sure what that does for older vehicles, I guess it will be the same as what there is today. Not surprising they brag this will remove 800,000 old cars, which proves their intent with SMOG laws. How exactly, I'm not clear; but this should make it easier for the newer cars and continue to be trouble for us classic car owners.
reference: SmogTips.com - AB 2289 - Smog Check Law California. No more tailpipe smog test. Elimination of tailpipe smog check testing for 2000 model vehicles and newer.

My '94 requires two cats and the new ones are the MagnaFlow direct replacement/fit CARB ones. PN's 36408 and 36409. I got a good deal and they still were over $700 for both.
Don't know if that will help you or not. My tech (my oldest son, works for Parker Motor Sports here in Apple Valley) ordered through NAPA or Autozone or O'Reilly, can't remember. If you have CARB approved ones they will be stamped. I know my old O2 sensors were crap as well.

Interesting on the new law. Once again penalizing those that appreciate auto history. Always has been about the money, not the air quality.

 

[AV8R]

[h=2]

Update March 7th[/h]

So we have tried just about everything...
- replaced cats, mufflers, EGR, Solenoid, ...
- checked EGR and back pressure on my system was not enough to run it properly (rags in muffler makes it work fine and the NOx comes way down)
- heads and valves cleaned
- consulted with "experts" that were recommended here

Our plan was that the new Magaflo cats and mufflers would do the trick with the OEM EGR, but there wasn't enough back pressure still.
Apparently the SMOG specs are getting tighter to the point where our aftermarket parts (cats, mufflers) cannot meet these tests (by design to rid old cars?).

While I was researching my problem, I found online that some guy with the same year vette as me had similar NOx numbers like mine.
What he did was use a Wells EGR and removed the ring washer and passed his tests. I told my mechanic about this and so he found a Wells EGR.
He installed it and removed the washer, and came close to passing. We have a few more things to try, like making sure the fuel pressure and pump are working properly.
We are thinking that this is working better because the Wells EGR spring doesn't require as much pressure to work as with the OEM GM Negative Pressure EGRs

Anyways, I have a good foundation by having new cats and muffler and cleaned exhaust. Im so close to passing now, wish me luck.
My mechanic almost gave up 2 times, but I cheered him on and sent him the ideas I found on the net to try, including what I read here.
As for what this is going to cost me... well lets say my wife wishes I sold this little beauty.​

 

[boomdriver]

If this is thought thru, it fails to make sense.

That EGR should have sufficient vac control pressure to operate when necessary BECAUSE the EGR generally only opens when the engine is under a load or bogs and THAT is when combustion temps shoot upward...the EGR is/was never intended to be only an emissions control device. It has benefits to emissions but its design purpose was to cool combustion to help prevent meltdowns with leaner/meaner engines as engine mngt technology evolved in the early 70s.

Is this EGR being expected to correct some other underlying problem? poor fuel control? air leak? worn injectors? worn valves/cam? Something is not right. If it were simply an issue with the neg/pressure EGR valve them there would be 100's of thousands of 80s, 90's and even 2000 yr model cars failing the test faster then they could line up.

Another thing..the "neg" pressure EGR is NOT operated/controlled by the exhaust. That "Negative" is in reality vacuum...
(neg pressure is vacuum)meaning it is vac operated. The big difference in the different type of EGR operations is the bleed off by way of a pin hole with a little ball/check/spring that allows exhaust to equalize and bleed off the vac thats holding the valve open. Thats how its able to close since the vac may remain and until there is positive pressure introduced. Like Hib said, stuffing a rag in the tail pipe forced each stroke to hold more used or burnt exhaust gas into the next cycle so the Nox went down briefly...same thing as the EGR opening and sending exhaust gas into the cylinder. Since we now know that the addition of exhaust does work in the right direction we need to focus on why that is not happening thru the design.

EGR operation is a balancing act of vac opposed to pressure...neg vs pos.

BTW, we need to clarify that the EGR is often described as "adding cold or burnt exhaust gas to the combustion process to cool it down"..... The word 'cold' is relative . Exhaust gas that is 1400 degrees IS colder than combustion thats up to 3000 degrees.
We want the EGR to open just enough to drop the combustion temps, which reduce the high oxides of nitrogen. Toxic and corrosive they are the by product of high combustion temps. So, when we lean out the fuel/air to lower the hydrocarbons, we raise the combustion temp and Nox. In order to lower THAT, we have to lower the temp of combustion without raising the hydrocarbons. We keep hydrocarbons DOWN by a good, high temp clean burn that completely burns all the fuel. The cat does the rest with an added shot of o2 to get that last little hydrocarbon molecule....so what does not burn is converted to harmless h20 vapor.
So, its a constant balance that we seek in the exhaust thats in need of constant adjustment because of the varying demands on the engine.

IF you Nox are wayyyy high, then manually operating the EGR would be an appropiate test. IF that helped, THEN move to discover whats preventing that from happening automatically....poor vac control, bad EGR valve itself, or restricted passage for the exhaust gas to flow and enter? Was the EGR tube ever replaced and welded in? could the passage be partially blocked? Again, if the egr lowers the Nox when operated manually with a vac pump..or even sucking on the hose, your engine may not be supplying the necessary vac to make it work well.

Take each fact and take it thru the many possibilities to the logical conclusion of each.

Is the engine performing well besides the poor emissions? low HC? No oil burning? I personally think that is wayy over-thinking the problem, and after many yrs of working with this type of thing,
I find Occams Razor to be most true and useful.

http://pespmc1.vub.ac.be/OCCAMRAZ.html

I hope that you get it figured out by tweeking the EGR or whatever has to be done, but after reading all this and watching from a distance I have to believe there is something simple thats causing the high numbers other than an EGR that was designed for that particular engine

Good Luck

 

[K & B Special Products]

EGR valve

FWIW, only Delphi makes the correct EGR valves for a GM engine. For example, an auto supply will show 1 valve that fits all, whereas Delphi breaks theirs down by OE part # & app.
The CA apps are also special. Call or PM me if you can't find one.

 

[roger longman]

Hi all, I don't know whether my experience will help but here goes......

In 2007 my '88 passed with NO readings of 83 and 61. scraped through on HC.
In 2009 NO readings of 98 and 75. scraped through on HC.
In 2011 NO readings of 106 and 85. failed HC reading 117 and 86. Replaced EGR (pintle broken) and O2 sensor.
Retested passed NO readings of 381 and 370. HC reading 78 and 60.

This was again scraping through on HC but substantially higher on NO. I'm sure someone, maybe Boom, will give the significance/cause of this but, I'm sure the allowances will be lower again next year and, my car might be looking for a new address........Roger.

 

[boomdriver]

ya know, IMO it comes down to 2 things...

the quality of the parts that are installed, as suggested above that the only correct EGR is the OEM Delphi. I have run into that with ignition parts and the aftermerket stuff just don;t cut it.

and...

the quality of the tune.

In order to achieve the level of performance that we, GM and the history book expect from every Corvette the tolerances and specs are pretty tight. Calibration and precision is the secret to high performance, acceptable cost. Step out of bounds and out of spec with cheap store brand parts and that can throw the calibration off.

As an example...

The bosch -III fuel injector.

Many many folks have done this upgrade/repair. 99.999% are extremely satisfied with the way their engines run after the install.
BUT,

there are also a large % that have the exact same cold start issues AFTER installing these injectors and so far, nobody has presented an across the board, acceptable explaination or a way to solve the problem.
MY theory is that the B-III are a different electrical value that somehow is seen or detected by the control system and the ECM has trouble when the eng is cold. I have tested cold, fuel pressure, ohms, sensors, name it, and the ONLY thing that makes a difference is the key ON to wake the ECM, off then ON and crank a second time. I can grind that starter for 10 seconds and it will not lite up. If I crank for 1 sec, release then try again its instant. That HAS to be some weird ECM electrical thing that other folks have experienced as well. Others have also found some relief by cranking and cold start the way I just described.
The problem?
A new part (injectors) thats not exactly the same electrical value as the stock part. Because these cars are tuned and operated by electrical resistence it does not take much to throw it all out of spec...whatever that is when seen by the ECM..

So, a smog analyzer will see what the engine is doing and the engine does what is within its operating parameters...the tune, and in these systems the Cal-Pak. The tune may be right but if the parts doing the work are not exact, the result may be unacceptable. I happen to know that the EGR valve is so strong that you can make it operate by sucking on the vac hose with your mouth....The diaphram is way bigger than is required to move that pintle...probably so it would operate with minimal available vacuum. If I am think this thru right...when the combustion temps shoot UP from a full throttle application, thats exactly when the vac falls off with the throttle suddenly WFO...a stiff or hard EGR spring may have trouble opening. Thats why I always LOOK with a mirror to watch the diaphram operate when I apply vac to the EGR.

This is/was my reference to Occams Razor...IMO points to the EGR valve when all the other possible and more complicated theories are removed from the picture. Simply stated, "what is most likely probably is".

 

[boomdriver]

Hi all, I don't know whether my experience will help but here goes......

In 2007 my '88 passed with NO readings of 83 and 61. scraped through on HC.
In 2009 NO readings of 98 and 75. scraped through on HC.
In 2011 NO readings of 106 and 85. failed HC reading 117 and 86. Replaced EGR (pintle broken) and O2 sensor.
Retested passed NO readings of 381 and 370. HC reading 78 and 60.

This was again scraping through on HC but substantially higher on NO. I'm sure someone, maybe Boom, will give the significance/cause of this but, I'm sure the allowances will be lower again next year and, my car might be looking for a new address........Roger.

I know of folks that do this in some neighboring areas...Its a common practice around Phx. In maricopa county they do smogs...in neighboring counties they do NOT...so lots of folks have a box at the UPS store across the county line...with a street address where the car is registered.

There is HUGE business opportunity here !

Buy up some land near the Ca borders...Az and Nev. Whats Northside of Ca? nuthin......Back to Az & Nv where its too hot for bunnys.. :L

Build as many PO Boxes as you can. Have a street address. Sell/rent these boxes to the Ca resident that is not ready to drive his car to the scrap yard because the Sacramento bunny huggers are unable to comprehend the concept of personal rights and gov intrusion in a never ending attempt to solve a crisis created by the media and believed by the mindless.:ugh

 

[AV8R]

Success! Perseverence and bucks

Before and after

 

[Hib Halverson]

Awesome, dude!

You got it to pass!

Nice work.

 

[navy2kcoupe]

Well done!
Perseverance pays off again!
Andy Anderson