HELP! failed emissions (Nox reading)
Thread Starter
Racer
Joined: Oct 2002
Posts: 470
Likes: 1
From: Kingwood TX
HELP! failed emissions (Nox reading)
The '91 failed the emissions test earlier today here were the readings:
High Speed:
HC 120=standard vette=28
CO 0.67=std. vette=0.02
Nox 848=std. vette=845
Dilution (%) >6.0= std. vette=14.0
Low Speed:
HC 124=std. vette=60
CO 0.69=std. vette=0.03
Nox 937=std. VETTE=1477
Dil. (%) >6.0=std vette=14.1
The emissions guy said that the temp seemed really high (~235) when they were doing the test and that might be a source of elevated Nox...is that true? My car has stock cam/internals with Accel runners and Accel base, muffler eliminators, eliminated pre-cats, 2000 stall B&M converter, and a one year old carsound catalytic converter. The smog pump has also been eliminated although the car has passed before without it or the pre-cats.
Any suggestions for reducing Nox would be greatly appreciated as would any potential sources of an elevated reading. Do any of the additives at auto stores that help in emissions reduce Nox or just hydrocarbons and CO?
TIA
High Speed:
HC 120=standard vette=28
CO 0.67=std. vette=0.02
Nox 848=std. vette=845
Dilution (%) >6.0= std. vette=14.0
Low Speed:
HC 124=std. vette=60
CO 0.69=std. vette=0.03
Nox 937=std. VETTE=1477
Dil. (%) >6.0=std vette=14.1
The emissions guy said that the temp seemed really high (~235) when they were doing the test and that might be a source of elevated Nox...is that true? My car has stock cam/internals with Accel runners and Accel base, muffler eliminators, eliminated pre-cats, 2000 stall B&M converter, and a one year old carsound catalytic converter. The smog pump has also been eliminated although the car has passed before without it or the pre-cats.
Any suggestions for reducing Nox would be greatly appreciated as would any potential sources of an elevated reading. Do any of the additives at auto stores that help in emissions reduce Nox or just hydrocarbons and CO?
TIA
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
NOx is aggravated by high combustion temps. The EGR valve lowers the combustion chamber temps by introducing an inert gas (exhaust) to reduce the temps. The EGR isn't likely the fault. Your NOx is borderline at at high speed, where the EGR is supposed to be open, and way over when it is supposed to be close at idle. Your HCs and COs are SO low, especially rhe CO, that I suspect an excessively lean mixture is causing higher combustion temps and therefore the high NOx number at idle. I would double check that the timing is properly set and spend the rest of my time looking for vacuum leaks.
RACE ON!!!
RACE ON!!!
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
I hope it proves fruitful. The vacuum leak(s) may be small and elusive, but I am reasonably confidant... The "quickness" was just a matter of being at the right place at the right time. Good luck, and...
RACE ON!!!
RACE ON!!!
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
You may want to check the EGR ports... if they get clogged up internal to the intake, all sorts of bad things happen.
As an example, Honda had a TSB on clogged EGR ports, and it would cause a crusing speed hic-up and increased NOx readings.
You may want to run some seafoam through the motor... never could hurt.
But I would seriously consider removing the EGR and checking out the port.
As an example, Honda had a TSB on clogged EGR ports, and it would cause a crusing speed hic-up and increased NOx readings.
You may want to run some seafoam through the motor... never could hurt.
But I would seriously consider removing the EGR and checking out the port.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
Ignition timing can also influence NOx.
Retarding the timing to the point at which the exhaust valve opens before combustion is completed should reduce NOx and HCs, but will negatively impact fuel economy.
As a temporary measure it may get you to pass. Has your timing been advanced either via chip or an increase in base timing.
Too much advance will hurt.
Retarding the timing to the point at which the exhaust valve opens before combustion is completed should reduce NOx and HCs, but will negatively impact fuel economy.
As a temporary measure it may get you to pass. Has your timing been advanced either via chip or an increase in base timing.
Too much advance will hurt.
Thread Starter
Racer
Joined: Oct 2002
Posts: 470
Likes: 1
From: Kingwood TX
I just got the car re-tested after adding the seafoam additive and kept both fans on via the manual fan switch that we had added several years ago. The Nox readings went down to like 145 on the high speed and around 550 on the low speed. So it passed without any EGR work or timing changes although those would have probably lowered these numbers even more. Thanks for everyone's input.
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Thread Starter
Racer
Joined: Oct 2002
Posts: 470
Likes: 1
From: Kingwood TX
Bogus, What type of problems are you possibly seeing indicated here ?Injector leaking , bad o2's , vacuum leak, egr problem,timing off?
This is my sons car,He got it @ 16 for being a straight A student since pre-school . He just graduated from " Trinity U ", still the only car he has ever owned. He will own it forever .
This is my sons car,He got it @ 16 for being a straight A student since pre-school . He just graduated from " Trinity U ", still the only car he has ever owned. He will own it forever .
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by WEH 2000C5
I just got the car re-tested after adding the seafoam additive and kept both fans on via the manual fan switch that we had added several years ago. The Nox readings went down to like 145 on the high speed and around 550 on the low speed. So it passed without any EGR work or timing changes although those would have probably lowered these numbers even more. Thanks for everyone's input.
RACE ON!!!
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by WEH 2000C5
Bogus, What type of problems are you possibly seeing indicated here ?Injector leaking , bad o2's , vacuum leak, egr problem,timing off?
This is my sons car,He got it @ 16 for being a straight A student since pre-school . He just graduated from " Trinity U ", still the only car he has ever owned. He will own it forever .
This is my sons car,He got it @ 16 for being a straight A student since pre-school . He just graduated from " Trinity U ", still the only car he has ever owned. He will own it forever .
If it was mine, I would just confirm a few things before putting the problem to bed... check the base timing and see where that, and the next time you have the intake apart, check the EGR...
At times, the best way to clean the intake and such is to hot tank it...
Heel & Toe
Joined: May 2003
Posts: 22
Likes: 0
From: Brampton ON
I had the exact same problem on my 95 last week. Fail emmisions on Nox, with really low Co2 and HC readings. Car was running too lean and combustion chamber temps too hot. My mechanic checked vaccum and it seemed okay. He ran a decarbonizer through the intake (GM stuff I think) and cleaned the rad of debris. It passed on the second attempt, but HC readings on the high side.
I had a guy in a Caddilac Catera in front of me who had the same problem. Mechanic clean out the rad and passed no problem.
Going to take it in next week to check if anything else.
I had a guy in a Caddilac Catera in front of me who had the same problem. Mechanic clean out the rad and passed no problem.
Going to take it in next week to check if anything else.
