[CA] high NOx
Joined: Mar 2000
Posts: 43,187
Likes: 42
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
NOx is formed with high pressure and temperature. The purpose of the EGR valve is to lower the combustion temperature. A non-operating EGR valve or plugged EGR passages will do it. You said the EGR passages were cleaned, does that mean the intake manifold was taken off and everything cleaned? If not, did you remove a lot of deposits from what you could get to? If the intake wasn't removed and you had deposits in what you could get to, then the rest of your EGR passages are probably plugged. An easy way to check is to manually open the EGR valve while the engine is idling - if it doesn't die, you've got clogged passages.
Other sources of high combustion temperature:
- Excessive compression (not likely, but can be cause by carbon deposits)
- Lean mixture
- Excessive spark advancement (aftermarket chips often cause this)
Other sources of high combustion temperature:
- Excessive compression (not likely, but can be cause by carbon deposits)
- Lean mixture
- Excessive spark advancement (aftermarket chips often cause this)
Junior Member
iTrader: (1)
Joined: May 2006
Posts: 25
Likes: 0
From: Calgary, Canada
Car: '89 Formula
Engine: 355 SBC, AFR 195s
Transmission: T-56 Swap
Axle/Gears: 7.5 Eaton LSD w 4.10s
Re: [CA] failed smog - high NOx
Take as much spark advance out as you can. I've had trouble with emissions testing for a couple of years now, but finally got it to pass... without an EGR valve. like mentioned above, check that the intake ports aren't clogged, cause EGR will be your best friend reducing NOx emissions. BUT the timing advance kills it too, and I was able to pass in all categories just by some creative tuning and as little ignition timing as the engine will run with (I was around 0 degrees while i usually run at 16).
Supreme Member
Joined: Jan 2000
Posts: 3,178
Likes: 48
From: Tracy, CA
Car: '87 IROC
Engine: LB9
Transmission: TH700R4
Re: [CA] failed smog - high NOx
'88 T/A 5.7 - 144k miles - recent purchase - car sat for 5 years
after reading many posts on high nox, I need more input
what I've done so far: 3" magna flow cat, oil change, fuel filter, plugs, wires, delphi egr, delphi coolant temp sensor, ac delco o2 sensor, ac delco TPS, IAC - delphi was used when ac delco not available
timing is set at 6* bdc
prior to changing out parts, I used Sea Foam in the engine and tank. the egr passages have been cleaned
any input is greatly appreaciated
after reading many posts on high nox, I need more input
what I've done so far: 3" magna flow cat, oil change, fuel filter, plugs, wires, delphi egr, delphi coolant temp sensor, ac delco o2 sensor, ac delco TPS, IAC - delphi was used when ac delco not available
timing is set at 6* bdc
prior to changing out parts, I used Sea Foam in the engine and tank. the egr passages have been cleaned
any input is greatly appreaciated
My car hasn't been driven much in the past 10 years (a little more than 2k miles) and I truly believe that this is part of the problem.
Member
Joined: Jan 2010
Posts: 295
Likes: 0
From: Burnaby, B.C.
Car: '78 GMC Sierra Heavy 1/2
Engine: GMPP ZZ4 Q-Jet
Transmission: 700R4 Stage 2 w/Race Internals
Axle/Gears: 10 Bolt 3:42 Eaton
Re: [CA] failed smog - high NOx
five7kid said all I wanted to say as I was going to add this...
NOx emissions are the result of high combustion chamber temps pure and simple. NOx readings go up whenever there are hot spots that exceed about 2400 degrees. Things like high compression and lean mixtures contribute to high chamber temps, as does over-advanced ignition timing.
NOx emissions are the result of high combustion chamber temps pure and simple. NOx readings go up whenever there are hot spots that exceed about 2400 degrees. Things like high compression and lean mixtures contribute to high chamber temps, as does over-advanced ignition timing.
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Joined: Jun 2009
Posts: 768
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From: Peoria, AZ
Car: 91 Z28, 2000 T/A
Engine: SBC 355, LS1
Transmission: T56, T56
Axle/Gears: 10bolt 3.73, 3.42
Re: [CA] failed smog - high NOx
My car sat for 9 years. The main things that brought my numbers down was a new EGR Valve with the Dyno Don drill mod brought it down about 1/2 a point, 1 can of Sea Foam ran through the intake brough it down nearly a full point, and then retarding the timing another 1/2 point. Also check you fuel pressure make sure it's up to spec.
Also go through in the morning. The cooler it is outside the better off you are. I noticed about .1-.2 rise in my numbers going through in during the middle of the day vs the morning/evening.
Since you have an free flowing aftermarket exhaust I recommend you do the EGR Drill mod. You Need a .040 drill bit, I picked up a #59 wire gauge one from ACE Hardware. It is the right size. You drill the hole larger in the nipple where the vacuum line hooks up, there is a night and day difference on how quickly/easily the EGR Valve opens.
Also go through in the morning. The cooler it is outside the better off you are. I noticed about .1-.2 rise in my numbers going through in during the middle of the day vs the morning/evening.
Since you have an free flowing aftermarket exhaust I recommend you do the EGR Drill mod. You Need a .040 drill bit, I picked up a #59 wire gauge one from ACE Hardware. It is the right size. You drill the hole larger in the nipple where the vacuum line hooks up, there is a night and day difference on how quickly/easily the EGR Valve opens.
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