1991 ZR1 Failed Emissions

[Jason 91]

Happy Thanksgiving everyone! :)

To my disappointment, my ZR1 failed its emissions test last week. I initially expected that it was the original injectors finally starting to go out and I was ready to replace them. I took the car to a local Corvette shop that has done work for me before and they told me that while the car may also need new injectors, one of the catalytic converters is bad.

I know that the exhaust manifold and catalytic converter are all one piece and no longer available so I’m unsure what to do at this point in time. I’d like to keep the car as close to stock as I can (if I start modifying this car, my discretionary spending won’t be able to keep up with my desires) and I need the car to pass emissions. What are my best options assuming one of the catalytic converters needs to be replaced? If I can find them, can I bolt the 1992 – 1995 exhaust manifold/catalytic converter set up to a 1991?

Here’s some other information that may or may not be of use to you.

49,300 miles on the odometer
No trouble codes
New plugs, wires, PCV valves, coolant and thermostat, fuel filter, Mobil 1 and filter and rear differential fluid
5,280 altitude

Thanks in advance for your help.

Jason

[gbrtng]

How were they able to isolate "one bad cat" since the flow from both sides gets mixed in the resonator? At 50,000 miles the original cats should still be pretty good. Better you post the test results and let us take a look before you start carving up the stock exhaust system. Also describe CO's test and what the pass/fail limits are.

[Ccmano]

How were they able to isolate "one bad cat" since the flow from both sides gets mixed in the resonator? At 50,000 miles the original cats should still be pretty good. Better you post the test results and let us take a look before you start carving up the stock exhaust system. Also describe CO's test and what the pass/fail limits are.

I agree, I wouldn't be too fast to jump on this. Remember, shops are generally unfamiliar with the Z. I just moved from Denver in the spring, which shop are you using? Generally there are no shops in Denver that are particularly good on the Z. The are some members that may be able to help you.

Are you failing because of HC or NOx issues? Do you have an aftermarket PROM? How do you know there are no codes?

Lots of questions.... Let us know.

Hans
:cheers:

[Jeffvette]

Give us all the details. ZR-1's can be a pain to get through the emissions program. A lot of states have been tightening standards on older cars.

[Z Factor]

A lot of states have been tightening standards on older cars.

All the more reason to live in a state like Florida with no emission tests.:thumbsup:

Happy Thanksgiving everyone! :)

]

Thanks

Happy Thanksgiving to you as well.

If it does turn out to be a cat, PM me as I know a guy down here with a set of stock manifolds/cats who might part with them.

:cheers:

[Jason 91]

Thanks for all of the quick replies – I really appreciate it. :cheers:

All,

Here’s a summary of the test results on 11/14;

Emissions Test Data
Fail HC GPM = 6.2399 with a limit of 2.5
Fail CO GPM = 46.2872 with a limit of 20.0
N/A CO2 GPM = 548.0899 with no limit specified
Pass NOx GPM = 2.6330 with a limit of 6.0

Visual
Pass Catalytic Converter
Pass Fuel Filler Restrictor
Fail Air Injection System The test facility would not tell me what they believed was missing and the shop believes that this was due to them not being familiar with the ZR1.
Pass Oxygen Sensor
Pass Check Engine Light

Here’s a summary of the prior test results on 10/7/05 less 1,428 miles on the odometer;

Pass HC GPM = 2.4750 with a limit of 2.5
Pass CO GPM = 14.5508 with a limit of 20.0
N/A CO2 GPM = 495.5999 with no limit specified
Pass NOx GPM = 2.9937 with a limit of 6.0

Visual
Pass Catalytic Converter
Pass Fuel Filler Restrictor
Pass Air Injection System
Pass Oxygen Sensor
Pass Check Engine Light

Here’s a link that explains the type of test that they do;

http://www.aircarecolorado.com

Gbrtng:

I’m not sure how they were able to isolate one cat being bad. I have not had any of the normal (i.e., rotten egg smell, hesitation, rattling) symptoms so I’m not certain. The guy I deal with is not real eager to drill holes or cut up the stock exhaust either which gives me some comfort. If it is a cat, I’m particularly concerned about what caused it to go bad in the first place.

Ccmano:

I took the car to Corvettes Only on Hampden and they are the ones who confirmed no codes. The PROM is not aftermarket.

http://www.corvettesonlydenver.com

Jeffvette:

I was originally concerned about the restrictions being tighter, but they are the same as they were two years ago so something must have happened between now and then. If it was close to the limits, I would have insisted driver error on the dyno and asked for a free retest. Tough to argue with what was being put out.

Z Factor:

That’s good to know. I will PM you if that’s the route I need to go.

Thanks,

Jason

[gbrtng]

Lots of HC and CO degradation in less than 1500 miles. I highly suspect a bad injector or two. The injector coil resistance can be measured at the ECM and should be in the range of 12 ohms. Anything less than 8 ohms should be replaced. Also, did you have fresh gasoline? Old fuel - more than 3 months old - might make a difference too. Were the engine and cats up to full operating temperatures when the test was run? If you have an infrared temperature gizmo you can shoot the cat temps which should be above 600 degrees or so - if one is cool, that's the weak one.

FWIW, the HC numbers two years ago were marginal.

[kenthompson]

I would probably be willing to remove mine, after I get the headers.

KT

[GOLDCYLON]

Thanks for all of the quick replies – I really appreciate it. :cheers:

All,

Here’s a summary of the test results on 11/14;

Emissions Test Data
Fail HC GPM = 6.2399 with a limit of 2.5
Fail CO GPM = 46.2872 with a limit of 20.0
N/A CO2 GPM = 548.0899 with no limit specified
Pass NOx GPM = 2.6330 with a limit of 6.0

Visual
Pass Catalytic Converter
Pass Fuel Filler Restrictor
Fail Air Injection System The test facility would not tell me what they believed was missing and the shop believes that this was due to them not being familiar with the ZR1.
Pass Oxygen Sensor
Pass Check Engine Light

Here’s a summary of the prior test results on 10/7/05 less 1,428 miles on the odometer;

Pass HC GPM = 2.4750 with a limit of 2.5
Pass CO GPM = 14.5508 with a limit of 20.0
N/A CO2 GPM = 495.5999 with no limit specified
Pass NOx GPM = 2.9937 with a limit of 6.0

Visual
Pass Catalytic Converter
Pass Fuel Filler Restrictor
Pass Air Injection System
Pass Oxygen Sensor
Pass Check Engine Light

Here’s a link that explains the type of test that they do;

http://www.aircarecolorado.com

Gbrtng:

I’m not sure how they were able to isolate one cat being bad. I have not had any of the normal (i.e., rotten egg smell, hesitation, rattling) symptoms so I’m not certain. The guy I deal with is not real eager to drill holes or cut up the stock exhaust either which gives me some comfort. If it is a cat, I’m particularly concerned about what caused it to go bad in the first place.

Ccmano:

I took the car to Corvettes Only on Hampden and they are the ones who confirmed no codes. The PROM is not aftermarket.

http://www.corvettesonlydenver.com

Jeffvette:

I was originally concerned about the restrictions being tighter, but they are the same as they were two years ago so something must have happened between now and then. If it was close to the limits, I would have insisted driver error on the dyno and asked for a free retest. Tough to argue with what was being put out.

Z Factor:

That’s good to know. I will PM you if that’s the route I need to go.

Thanks,

Jason


Jason I had reading like this on my 91 and the culprit was indeed a bad o2 sensor and a bad cat on the passenger side. Upon inspection the honeycomb was completely gone on the right cat side. The specualtion was that the cat was dropped and the bits went into the resonator. We thought it was possible somebody punched the cat however with an uncomprimised cat on the driver side we detemined that was unlikely this was the best guess we could come up with. We replaced the cat and the 02 sensor problem solved.

[tomtom72]

I'm no mechanic Jason, but I agree with Glenn. You seem to have done the tune up stuff...save the coils....they could be weak which would contribute to dirty exhaust. O2 sensors may be lazy....mine were after 16 yrs.I swapped them out and my test scores improved dramatically. I'd want to see the scan data on the O2's. Are the injectors OE? before my OEM injectors failed they did a bit of telegraphing via scan results....but I was too ignorant to see the warnings.:o

Maybe tap the cats a bit to see if anything is rattlin' in them? The I/R probe is proly best bet but the tap test sometimes yields results.

Our AIR pumps are electric so maybe the inspector missed that? Yours is still there, left front under the headlight? Maybe the purge canister/ evap. system is worth looking at?....to me it's a long shot but if all else fails??

:cheers:
Tom

Hey Jason, I'm not trying to be smart. Please look at this link and then look at your emissions' test results and think about what's going on. To me it seems unlikely that the cats are bad, old matbe but not shot. JMHO
http://en.wikipedia.org/wiki/Catalytic_converter

[Jason 91]

Gbrtng:

The degradation is the main reason I initially thought it was the OE injectors failing.

The gasoline was fresh. Before I took it in for the test, I drained the tank by driving it back and forth between Denver and my CO Springs office which is about 55 miles each way. I refilled it shortly before going to take the test. Also, the car was up to normal operating temperature. The frustrating thing, and I’m not sure if this made a difference, was having to idle for about 45 minutes while waiting in line. This caused the fans to come on a couple of times. :censored:

Goldcylon:

Where did you get the 1991 exhaust manifold/catalytic converter from? Did you get it from another member? I just had a member reach out to me. Thanks Greg! :cheers:

Tomtom72:

The injectors are OE and with the ethanol here, I expect to be replacing them soon either way. Is there specific scan data we should look at that demonstrates the injectors are going bad or is it you need to see a continuing rise/decline in specific results?

I’m not going to let them fail me again for the air injection system after I’ve confirmed that all original equipment is in good working order.

Thanks for the link. I’m still learning (you seem like more of a mechanic than me :) ) and information is always helpful.

All:

Feel free to comment on any of these above responses. I’m trying to make sure that I respond to all questions asked because I really appreciate you guys taking the time to help me.

I will verify that it is in fact the cat that is bad before anything gets cut, but I have a couple of questions assuming that it is.

Assuming the exhaust manifold/catalytic converter needs to be replaced, how much R & R labor hours am I looking at for each? I’ve read the FSM (and Chilton’s for what it’s worth), but I have little practical experience so I’m having trouble figuring it out and am probably oversimplifying it.

Is a universal cat even an option as a last resort (I see some for sale)?

Are there any header options that I could still pass emissions with assuming everything else is in good working order?

Again, I appreciate all of the help you guys are giving me.

Thanks,

Jason

[Aurora40]

Just FWIW, here is the difference new injectors made on mine, with all within fairly acceptable ohm readings. My injectors leaked, if you pulled the fuel rail you could watch the drops form on them. I could also smell gas if I cracked the throttle body an hour or more after shutting the car down.

Anyway, VA doesn't do GPM. But here is what happened:

Before:
HC 30 PPM @ 15mph / 76 PPM @ 25mph
CO .06% @ 15mph / .08% @ 25mph

After:
HC 13 PPM @ 15mph / 13 PPM @ 25mph
CO .05% @ 15mph / .02% @ 25mph

The other change along with the injectors was a ported intake and a Haibeck chip. Though I believe the injectors are the reason for the emissions cleanup.

On the topic of cats, I believe the '93+ two piece manifold/cat can be put on the early cars. And it should fit up to the exhaust. I believe they are still available new from GM. You also could buy the '90-92 style ones used. Or you could just make the jump to headers and cats. Or possibly try to track down a set of Callaway (Lingenfelter sold them too I believe) header/cats if you want some gain from a stock type manifold.

I don't believe you could very attractively replace it with a universal cat? You'd presumably have to gut out the factory cat, then cut/weld in a universal one somewhere downstream.

[Jeffvette]

Just for grins after seeing you post GPM, the testing in Colorado uses the IM 240 testing standards. A clean running ZR-1 will have problems going through the test as it is so dependant on the tester being able to drive the car correctly.

We used to have the 240 test in Oregon and they phased it out as it was to expensive and also was not generating the results they wanted.

Are you failing on the accel or decel portion of the test?

[gbrtng]

Mine made the fast pass (90 seconds) IM240 test in IL in 2003 after lots of expense. New O2 sensors, and a fresh set of cats with headers didn't make much difference to the HC numbers. Finally Haibeck diagnosed a leaking vapor canister - which is in the right rear fender right where the IM240 exhaust hose picks the exhaust - and a replacement cannister cleaned her up.
This is on s 44,000 mile car with original injectors. This does not compare with Jason's problem because mine was OK on all but the HC numbers. Point being that each vehicle is different with its specific problems. At least in IL you have the option to declare a vehicle a "race car" making it exempt from testing. Maybe CO has some trick exemption you can use ...

[Bill]

Jason, If you need some hands on wrenching? I met these guys last June during CruiseFest. I lost a primary fuel pump, They got me running in short order and a reasonable price. I don't know if they do smog, but they know their stuff.
Good folks and close to you
http://www.corvettecenterusa.com/

[Zr1 Destroyer]

Hit me up......i have an emisions only flow master sytem that i use for my Zr1.


I removed the center muffler for a cat converter and the Y pipe just after the factory headers has one cat welded in place for a total of three cats just on the flow master system!

Also if you try it again flog the living hell out of it for about 20 minutes to blow all that crap out and to heat the hell out of the factory cats! Is your air pump working?

Ry in thornton, co.

[Zr1 Destroyer]

Gbrtng:

The degradation is the main reason I initially thought it was the OE injectors failing.

The gasoline was fresh. Before I took it in for the test, I drained the tank by driving it back and forth between Denver and my CO Springs office which is about 55 miles each way. I refilled it shortly before going to take the test. Also, the car was up to normal operating temperature. The frustrating thing, and I’m not sure if this made a difference, was having to idle for about 45 minutes while waiting in line. This caused the fans to come on a couple of times. :censored:

Goldcylon:

Where did you get the 1991 exhaust manifold/catalytic converter from? Did you get it from another member? I just had a member reach out to me. Thanks Greg! :cheers:

Tomtom72:

The injectors are OE and with the ethanol here, I expect to be replacing them soon either way. Is there specific scan data we should look at that demonstrates the injectors are going bad or is it you need to see a continuing rise/decline in specific results?

I’m not going to let them fail me again for the air injection system after I’ve confirmed that all original equipment is in good working order.

Thanks for the link. I’m still learning (you seem like more of a mechanic than me :) ) and information is always helpful.

All:

Feel free to comment on any of these above responses. I’m trying to make sure that I respond to all questions asked because I really appreciate you guys taking the time to help me.

I will verify that it is in fact the cat that is bad before anything gets cut, but I have a couple of questions assuming that it is.

Assuming the exhaust manifold/catalytic converter needs to be replaced, how much R & R labor hours am I looking at for each? I’ve read the FSM (and Chilton’s for what it’s worth), but I have little practical experience so I’m having trouble figuring it out and am probably oversimplifying it.

Is a universal cat even an option as a last resort (I see some for sale)?

Are there any header options that I could still pass emissions with assuming everything else is in good working order?

Again, I appreciate all of the help you guys are giving me.

Thanks,

JasonDo you have a scan tool? Also have you changed the o2 sensors lately?

[Jason 91]

Aurora40:

New injectors are in my near if not immediate future. Thanks for the answer on the 93 + MY setup.

Jeffvette:

I gave the graph to the guy at the shop, but from what I recall, I was failing consistently based on my interpretation of the graph.
The state acknowledges that there is some driver dependency on the dyno and I will fight them if I can at least get close. It’s frustrating that it’s always going to be close though. :censored:

Gbrtng:

There are some exemptions that I could exercise, but I really want to get the car in good working order. It drove well to me so this is a little bit of a surprise. It would be nice to simply declare it a “race car” and get my current registration though. :mrgreen:

Bill:

Thanks for the tip. I believe that I spoke to those guys one time before. I saw their site on a drive I was making and they gave me a pretty reasonable quote on replacing the weather stripping.

ZR1 Destroyer:

I appreciate the offer. :cheers:
I live in Washington Park so I’m not to far away from you. So essentially you bolt this item on and it cleans up the exhaust for the test?
The air pump is functioning appropriately, but the O2 sensors are original and probably part of the upstream problem because I’ve had no trouble codes. I do not have a scan tool, but I need to get one because they are a necessity.

Thanks,

Jason

[Zr1 Destroyer]

ZR1 Destroyer:

I appreciate the offer. :cheers:
I live in Washington Park so I’m not to far away from you. So essentially you bolt this item on and it cleans up the exhaust for the test?
The air pump is functioning appropriately, but the O2 sensors are original and probably part of the upstream problem because I’ve had no trouble codes. I do not have a scan tool, but I need to get one because they are a necessity.

Thanks,

Jason
[/quote]The emisions only system i have just ads a few more cats in the mix is all. I used for my old 368 that had a more then hard time passing the colorado e test.

If you ever want to pop your plenum off for any reason or just need help in general......also have a scanner that works nicely.

Ry:hello:

[WB9MCW]

"At least in IL you have the option to declare a vehicle a "race car" making it exempt from testing."


The big news in IL is now only 96 and up have to be tested so all ZR-1's get off the hook now!!!!:thumbsup: :cheers:

[Zr1 Destroyer]

"At least in IL you have the option to declare a vehicle a "race car" making it exempt from testing."


The big news in IL is now only 96 and up have to be tested so all ZR-1's get off the hook now!!!!:thumbsup: :cheers:Wow...that'd be nice, but it takes a while for our little cow town to catch onto things....lol!

I finally gave up after i did a leak down test on my old 368 and registered it about 30 miles away from my house in a non E test part of the county! After pulling my 368 apart it was obvious to me why i couldn't pass!

[WB9MCW]

Wow...that'd be nice, but it takes a while for our little cow town to catch onto things....lol!

I finally gave up after i did a leak down test on my old 368 and registered it about 30 miles away from my house in a non E test part of the county! After pulling my 368 apart it was obvious to me why i couldn't pass!


Yep that was what I used to be doing was having it reg. at my buddy's shop outside of the test zone.

Sure is nice to have to have the renewals show up at the home now!

[gbrtng]

When I moved from IL in 2003 the IM240 test was on the basis of ZIP code and the entire Chicago area was included. Shortly thereafter all OBDII cars (96 and newer) were passed if there was no check engine light. So now there are no tests for anything earlier than 1996 at all?

[WB9MCW]

Yep the Gov. cut the testing because of the bad deficit in IL.

NO testing for the KOTH or anything pre OBDII.

Tis good to live in ILLINOISEY now!!!!

[gbrtng]

Yep the Gov. cut the testing because of the bad deficit in IL.

NO testing for the KOTH or anything pre OBDII.

Tis good to live in ILLINOISEY now!!!!
Well, maybe it's better, but there's a long way to good yet. And that's the first sensible thing your governor has done. Whatta loser =D>

[WB9MCW]

Well, maybe it's better, but there's a long way to good yet. And that's the first sensible thing your governor has done. Whatta loser =D>


No argument there abt the crappy Gov.!!!!

The only good part is that now a cat free header free flow exhaust system makes sense!!!

B&B baby --- time for sum resonance!!! :thumbsup:

Get it now--- "IL A NOISY" :sign10:

[Jason 91]

I wanted to circle back and let you guys know that my car passed once the exhaust manifold/catalytic converter was swapped. :)

Again, I appreciate all of the support and knowledge that you all shared on this post.

A special thanks to Greg (sgreg) for giving me such a fair deal on the set.

Greg, it meant a lot and I really appreciate it. :handshak:

Thanks,

Jason

[carter200]

Sgreg is a good guy :thumbsup:

[GOLDCYLON]

I wanted to circle back and let you guys know that my car passed once the exhaust manifold/catalytic converter was swapped. :)

Again, I appreciate all of the support and knowledge that you all shared on this post.

A special thanks to Greg (sgreg) for giving me such a fair deal on the set.

Greg, it meant a lot and I really appreciate it. :handshak:

Thanks,

Jason

Told you so.... Congrats