failed emissions again... suggestions?
Thread Starter
Racer
Joined: May 2005
Posts: 360
Likes: 0
From: Canton GA
failed emissions again... suggestions?
1985 - sat for 5yrs before I got ahold of it... its running really good (sotp) but...
First failure gave these numbers:
HC - 134 (allowed 152) and 134 (157)
CO% - 1.80 (0.97) and 1.95 (0.88)
NOx - 421 (1082) and 568 (1184)
Then, replaced upper and lower runner gaskets, throttle body gasket, upper and lower injector o-rings + replaced injectors (from an 86)... new wires, plugs, o2 sensor, drained/cleaned/flushed cooling system... cleared the computer and put about 100+mi on it...
Test results from today:
HC - 103 (152) and 133 (157)
CO% - 1.55 (0.97) and 1.73 (0.88)
NOx - 483 (1082) and 649 (1184)
CO% went down, but not hardly enough to make it pass... the other stuff is fine it seems...
What else can I check? I'm thinking maybe timing and fuel pressure?? Other than that, unless the o2 is bad, I'm lost.
First failure gave these numbers:
HC - 134 (allowed 152) and 134 (157)
CO% - 1.80 (0.97) and 1.95 (0.88)
NOx - 421 (1082) and 568 (1184)
Then, replaced upper and lower runner gaskets, throttle body gasket, upper and lower injector o-rings + replaced injectors (from an 86)... new wires, plugs, o2 sensor, drained/cleaned/flushed cooling system... cleared the computer and put about 100+mi on it...
Test results from today:
HC - 103 (152) and 133 (157)
CO% - 1.55 (0.97) and 1.73 (0.88)
NOx - 483 (1082) and 649 (1184)
CO% went down, but not hardly enough to make it pass... the other stuff is fine it seems...
What else can I check? I'm thinking maybe timing and fuel pressure?? Other than that, unless the o2 is bad, I'm lost.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
It is still running rich. The HCs tell you that you are burning most of the fuel, but the CO tells you the mixture is still too rich. When you lean it out the NOx will likely jump, but you have plenty of head room, there.
RACE ON!!!
RACE ON!!!
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
High CO
As CFI-EFI said it is still rich, I would check the 86 injector flow rate to be sure it is the same as your 85, and checking the fuel pressure won't hurt but would be unusual to be high unless you have made changes. Could be a weak CAT too, best of luck.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
You're right, that sounds like it is getting warm enough, the CAT is still a possibility. Sometimes checking inlet and outlet temps will tell you if it's working but not always, wish I had another suggestion.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
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
Thread Starter
Racer
Joined: May 2005
Posts: 360
Likes: 0
From: Canton GA
we shoved a wideband sensor far up the tail pipe and it was reading pretty good... ~15.1 @ idle and it never really bad when we free revved it either...
before all the repairs we did, it was off the scale lean (over 21:1) at idle, so I know the repairs made a big difference...
I guess that cat is bad... thats the only thing left really...
I always thought if the cat was bad, all the emissions would be way off, but I guess not...
before all the repairs we did, it was off the scale lean (over 21:1) at idle, so I know the repairs made a big difference...
I guess that cat is bad... thats the only thing left really...
I always thought if the cat was bad, all the emissions would be way off, but I guess not...
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
bad cat
HC will usually only climb if you have a misfire, newer CATS are 3 way and control NOX somewhat but I'm not sure older ones do. As CFI-EFI indicated too, high CO will lower NOX, that could be why it is okay.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by Thrak
I guess that cat is bad... thats the only thing left really...
Originally Posted by Thrak
Test results from today:
HC - 103 (152) and 133 (157)......64 (220) and 120 (220)
CO% - 1.55 (0.97) and 1.73 (0.88)......1.51 (1.20) and 1.17 (1.20)
NOx - 483 (1082) and 649 (1184)......Not tested.
HC - 103 (152) and 133 (157)......64 (220) and 120 (220)
CO% - 1.55 (0.97) and 1.73 (0.88)......1.51 (1.20) and 1.17 (1.20)
NOx - 483 (1082) and 649 (1184)......Not tested.
RACE ON!!!
Thread Starter
Racer
Joined: May 2005
Posts: 360
Likes: 0
From: Canton GA
thats weird...so, my numbers are higher than a car w/ no cat lol... if my cat wasnt working at all, I'd expect numbers like yours.. which I have, right?
*sigh*
I dont know where else to check for air... I'm about at my limit...
*sigh*
I dont know where else to check for air... I'm about at my limit...
Last edited by Thrak; Jul 29, 2006 at 06:20 PM.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
I'm not saying that cats aren't effective. What I AM pointing out, is that your numbers can be much better, even if your cat is bad. I have a pretty good idea where MY high CO numbers come from. As an illustration, I have a 1978 GMC 3/4 ton pick up with a 400 CID, Quadrajet 4 bbl engine. The GVW of the truck is over 7500 pounds, so it has, "heavy duty emissions". That means that it has no EGR, no smog pump, and no cat. Of course it has no O2 sensor and no computer. The standards it must meet to pass are:
HC: 1200, 1200
CO: 5.00, 5.00
NOx: Not regulated
Test results:
HC: 71, 117
CO: .92, .71
NOx: Not tested
That dirty old truck not only passes the test for my '84, it passes your test, too.
RACE ON!!!
HC: 1200, 1200
CO: 5.00, 5.00
NOx: Not regulated
Test results:
HC: 71, 117
CO: .92, .71
NOx: Not tested
That dirty old truck not only passes the test for my '84, it passes your test, too.
RACE ON!!!
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
I would never suggest replacing a cat as a cure all for an emmision problem, quite the opposite actually, it would be a last resort after exhausting all other possibilities, no pun intended.
One other thought on the above failure would be to check the air injection. Seeing some engine data would help too if you have it.
One other thought on the above failure would be to check the air injection. Seeing some engine data would help too if you have it.
Thread Starter
Racer
Joined: May 2005
Posts: 360
Likes: 0
From: Canton GA
We're going to check timing first.. then try to get some data.. even though we're new at this whole data thing.
I'd rather not replace that cat, so I am going to try all other options first.
I'll be making my way to the Scan & Tune section shortly.
Any and all suggestions are welcome!!
I'd rather not replace that cat, so I am going to try all other options first.
I'll be making my way to the Scan & Tune section shortly.
Any and all suggestions are welcome!!
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by CTYANK2
Well at least the emission standards there are reasonable. Limits here in Connecticut are:
HC: 0.88
CO: 0.28
Nox: 614
HC: 0.88
CO: 0.28
Nox: 614
RACE ON!!!