I just failed emissions inspection in the oppressive state of New Jersey.

HC was just a little high (220 ppm is the tolerance, 297 ppm was the reading)
CO was very high (1.2% is the tolerance, 3.49% was the reading)
CO2 was fine..

this was during the IDLE portion of the test
the 'high idle' portion of the test when the pedal the car to about 3000rpm i passed with flying colors

the car runs/drives amazingly, i have no codes / service engine soon light, and no known problems, the car has passed inspection every 2 years without problems since I've owned it in 1999

stock LT1 / Z28 except for:
Borla Exhaust, K&N filter, MSD optispark replacement with custom vacuum line put on it like the newer models have to suck the moisture out, and I believe a 160 thermostat

here's something i'm thinking... granted due to the 160 thermostat, and the fiberglass scoop hood that is a replica of a 67 big block vette which allows all the hot air to escape in a hurry, the car normally runs very cool

however, i took a ride the other night, very cold night (like 20 degrees outside) and the car NEVER warmed up, the engine, (and interior!) were below normal temp for the full maybe 100 miles it seemed

can a bad thermostat (stuck open?) cause high emissions? i waited in line for the inspection thing today for about 20 minutes and the fan never turned on, the car seemed to be about 160 or 170 I'd say the whole time, and its about 30 degrees and cloudy outside

am i making up a solution that is impractical here, or do you think i'm on to something and should try this nice cheap fix and get a factory thermostat ... do you think have the car on the verge of overheating (like i always remember it being years ago with factory thermostat) would make it run leaner and result in lower CO emissions?

i'm ok with / prefer the higher temp factory one at this point anyway... the car is 20 years old and i rarely do anything high performance anymore, i just take it for late night rides once a month or so once the kids are asleep, its not a daily driver and never raced anymore... what is the factory one for a 93 lt1 .. 180 or 195 ?

thanks for your time and merry christmas

 

Yes, as combustion chamber temp goes down, HC and CO go up. NOx (which you didn't mention) goes down. Fuel mileage will drop as well. That's why the factory wants it to run at 210*F, the middle of the gauge.

Stock t'stat is 180*F (due to the reverse flow cooling system).

The problem could also be the result of declining cat performance.

 

since the car was running on the richer side all along with the 160 tstat, and probably richer lately with what probably is a stuck open tstat... do you think the catalytic converter could be more shot than you'd expect at 66k miles (since its 20 years old anyway) anyone have any experience with that cat? is it truly a direct fit bolt on or is it a headache on the 93/94 years?

i'm just thinking of routes like tstat and cat because i'm not getting any codes from any engine sensors.. pre 95 has limited sensors which is good and bad at times

these are the two cats i've looked at:
MagnaFlow 93444
and
Flowmaster 2010010

any other no-code solutions anyone can think of?

 

anyone else have more input on this please?

 

In California the smog places like a hot engine.I used to sit in the parking lot for a few minutes and wait for the fans to come on before running the test.I stayed with the 180 thermo.I also changed the oil before every test.Hope this helps.

 

Incorrect.

The catalytic converter promotes the oxidation of unburned HC, the oxidation of CO (which together are converted to H2O and CO2. reducing the molar quantity of HC and CO), and promotes the reduction (a chemical reaction, not a "reduction" of quantity) of NOx. The NOx is "reduced" to N2 and O2.

End result - the cat reduces the quantity of HC, CO and NOx in the exhaust.

 

Injuneer is right again.I had to have a cat replaced on another car and the place told me if the cat is 5% off,it will kick the dash light on.Bottom line,keep the air cleaner clean,keep the plugs up to parr,change the oil,so the engine will burn clean to start with.The cat does not like unburned gas.Whew.My02.

 

Depends on whether its OBD-1 or OBD-2. OBD-1 has no monitor capability of cat efficiency. That capability was added in 1996 as required by OBD-2.

 

ok... 6 months later.. I'm legal again

we had about 22 (no lie) snow storms between december and march, and we just had our 2nd baby 3 months ago, so the 'spare car' was on the back burner until recently

To get through inspection I:
-I went with the Magnaflow 93444 direct-fit catalytic converter & y-pipe kit. (from convertershack.com)
-Cleaned my K&N filter

Also I switched back to the OEM thermostat, I used to have a 160 but my days of caring about that are done. Also changed the oil and fixed a vacuum leak connected to the optispark unit (1993 didn't have a vented optispark, but I have the upgraded MSD optispark with provision for venting, and used the 1995 vacuum line kit GM part # 12555323 for $53+ shipping from gmpartsheadquarters.com

FYI I broke the first stud when trying to change the cat/ypipe myself on the garage floor, so I knew I was in over my head on that part of the job since I don't have a lift or a torch... so I resorted to a local garage who replaced the cat/ypipe with MY part and did the state inspection for $190, which is very good for NJ.

End result... the government will let me drive my car again... thank heavens another criminal off the roads lol...

I'm not sure if they even used my car for the smog test or pulled in a new hyundai... but these guys aren't friends so I'm not sure why they would do that, but the results seem drastic...

Before..
@ Idle
HC PPM actual 297 (allowed 220)
CO% actual 3.49 (allowed 1.20)
@ High Idle
HC PPM 118 (allowed 220)
CO% actual 1.17 (allowed 1.2)


After..
@ Idle
HC PPM actual 150 (allowed 220)
CO% actual .30 (allowed 1.20)
@ High Idle
HC PPM 71 (allowed 220)
CO% actual .50 (allowed 1.2)

The amazing thing is how the car feels... that old cat must have been bad for years. The before and after is amazing... I just about wrecked coming out of the shop parking lot the car is so strong now.. and louder than ever. I feel like there was a dead squirrell living in my old cat compared to now.

 

Glad you got it worked out.

 

No problem...

I'm an amateur mechanic (I'm a CPA). I have a decent amount of tools and space to work, but I heavily rely on forums for research for diagnostics... so if I can contribute back and help someone else I'm glad to do it. My father is a lifelong mechanic/electrician (by profession he works on cargo cranes, but he knows everything about cars from the 80's and older) but he's near retirement age and doesn't have the time & energy or technology experience... he'll rebuild your engine pre-OBD-anything, but don't ask him to read a printout from a modern emission inspection.

Also an FYI ... I intended to get a new K&N filter just because mine is like 15 years old and has been a little banged up... but I had to end up cleaning/reusing again. I have the 'cold air kit' that APPEARS similar to current part # 57-3010-1... however they must have changed something over the years since I got that many years ago... the recommended replacement filter RF-1015 is not the proper size/shape for the older version of the cold air kit I apparently have... and K&N is not providing me with any other info on the matter, thankfully they are at least accepting a return for a full refund.

 

The Moroso was a duplicate of the Callaway Honker. I had the callaway 19 years ago.