So My car failed Emissions...
Thread Starter
Safety Car
Joined: Jan 2006
Posts: 3,566
Likes: 4
From: Mt Laurel NJ
St. Jude Donor '06-'07
So My car failed Emissions...
My car (1990 L98) recently failed it's emission test for high NOx. The is basically stock w/ 24lb injectors, true dual exhaust w/ cats, and a custom chip to delete the EGR, which has been removed. The car has a recent tune up, w/ new plugs, wires, cap, fuel filter. It had it's intake removed and resealed using FelPro gaskets last April. Other then that, the car runs great, w/ no problems at all. Mileage is about 102K.
The strange thing to me is that it was well within the limits of the other two categories.
This what the test said;
hydrocarbons 1.4000gpm -0.4612 pass
carbon monoxide 30.0000gpm -5.1493 pass
oxides of nitrogen 2.5000gpm -2.8883 fail
Anyone have any ideas as to why it failed?
Thanks, Randy
The strange thing to me is that it was well within the limits of the other two categories.
This what the test said;
hydrocarbons 1.4000gpm -0.4612 pass
carbon monoxide 30.0000gpm -5.1493 pass
oxides of nitrogen 2.5000gpm -2.8883 fail
Anyone have any ideas as to why it failed?
Thanks, Randy
Thread Starter
Safety Car
Joined: Jan 2006
Posts: 3,566
Likes: 4
From: Mt Laurel NJ
St. Jude Donor '06-'07
Corvette Enthusiast
Joined: Oct 2007
Posts: 6,795
Likes: 2,717
From: So. Cal.
2025 C7 of the Year Finalist- Unmodified
2024 C7 of the Year Finalist - Unmodified
2023 C7 of the Year Finalist - Unmodified
Safety Car
Joined: Jan 2004
Posts: 3,783
Likes: 15
From: Northern California
High NOX levels are directly related to the EGR delete as mentioned earlier.
The EGR valve lowers the combustion temperatures which, when removed is why the NOX levels were higher than allowed.
Each State has different emmision standards which is why some who have removed the egr have still passed.
The EGR valve lowers the combustion temperatures which, when removed is why the NOX levels were higher than allowed.
Each State has different emmision standards which is why some who have removed the egr have still passed.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Intermediate
Joined: Apr 2009
Posts: 34
Likes: 0
From: Huntington Beach California
Randy,
Gotta believe it's the EGR delete, is this the first test without it? Did you discuss this with the chip guy to find out what changes he made to compensate for the EGR delete (i.e. richer mixtures, etc.)? Was the test done at idle or on a dyno?
Maybe trying to get the engine to run cooler (lower temp thermostat) would get you through the test, worth a try. Gotta keep as many of these charcoal ones going as we can.
I've got a pretty much stock setup (cat back exhaust only) and my NOx was good last test (about 13% of the allowable at 15 mph & 9% at 25 mph). I believe the EGR passes more at the higher speed.
Kab3
Gotta believe it's the EGR delete, is this the first test without it? Did you discuss this with the chip guy to find out what changes he made to compensate for the EGR delete (i.e. richer mixtures, etc.)? Was the test done at idle or on a dyno?
Maybe trying to get the engine to run cooler (lower temp thermostat) would get you through the test, worth a try. Gotta keep as many of these charcoal ones going as we can.
I've got a pretty much stock setup (cat back exhaust only) and my NOx was good last test (about 13% of the allowable at 15 mph & 9% at 25 mph). I believe the EGR passes more at the higher speed.
Kab3
Thread Starter
Safety Car
Joined: Jan 2006
Posts: 3,566
Likes: 4
From: Mt Laurel NJ
St. Jude Donor '06-'07
The reason the EGR was deleted is because it set a code after the new exhaust system was installed. Everything was fine w/ it before the change, it seems that speed density cars need a certain amount of back pressure for the EGR to work correctly, so I really had no choice. That is the reason the car has a custom chip, to delete the EGR.
Drifting
Joined: Sep 2002
Posts: 1,642
Likes: 0
From: Suwanee,Ga
The reason the EGR was deleted is because it set a code after the new exhaust system was installed. Everything was fine w/ it before the change, it seems that speed density cars need a certain amount of back pressure for the EGR to work correctly, so I really had no choice. That is the reason the car has a custom chip, to delete the EGR.
This is the purpose of the silly thing.
This does not sound at all like a chip issue. If it set a code it was likely the Temp Indicator The little gizmo that goes into the EGR tube, right as it enter the intake.
Without EGR, on a basically stock motor, you could be getting a good bit more knock, and may run hotter, & FAIL Emissions!!!
TJM
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
My car (1990 L98) recently failed it's emission test for high NOx. The is basically stock w/ 24lb injectors, true dual exhaust w/ cats, and a custom chip to delete the EGR, which has been removed. The car has a recent tune up, w/ new plugs, wires, cap, fuel filter. It had it's intake removed and resealed using FelPro gaskets last April. Other then that, the car runs great, w/ no problems at all. Mileage is about 102K.
The strange thing to me is that it was well within the limits of the other two categories.
This what the test said;
hydrocarbons 1.4000gpm -0.4612 pass
carbon monoxide 30.0000gpm -5.1493 pass
oxides of nitrogen 2.5000gpm -2.8883 fail
Anyone have any ideas as to why it failed?
Thanks, Randy
The strange thing to me is that it was well within the limits of the other two categories.
This what the test said;
hydrocarbons 1.4000gpm -0.4612 pass
carbon monoxide 30.0000gpm -5.1493 pass
oxides of nitrogen 2.5000gpm -2.8883 fail
Anyone have any ideas as to why it failed?
Thanks, Randy
The problem is the lack of EGR, you may be able to pass the test by retarding your timing, lowering the water temperature to reduce combustion temperature, or running a higher octane fuel that may burn cooler at low loads. If that does not work you may be forced to put the EGR back on to pass the test.
I just did a little research and a failed catalytic convertor is also listed as a possible reason for high NoX readings, you may want to check into this a little more.
Last edited by bjankuski; May 15, 2009 at 03:21 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Might be/Should be - but the 3 way Cat along with EGR scrubs up about 60 to 70% of NOX emissions and if the knock sensor chimes in, it retards timing and fattens it up. That shortens the life of the CAT. Looking at the HC and CO numbers, it doesn't look bad, so hopefully reconnecting EGR makes it pass OR if these are idle numbers and not cruise, it is the CAT (and it's possibly lean) because EGR isn't doing anything at idle. Otherwise, without a scan, you don't know what it's doing and scanning it under all possible conditions isn't an easy task, but you might just run one to narrow it down.
Drifting
Joined: Oct 2006
Posts: 1,328
Likes: 14
From: Stafford Connecticut
I have passed emissions after failing by retarding timing and adding two cans of Dry Gas additive to the gas tank. Just be careful not to retard timing to much or the other numbers could go up.