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Smog Help Needed!!

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four50NCalif

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Bay Area California
So the deal is that I have a slightly modded 1981 Blazer, has a cam headers and intake manifold. I have a true dual exhaust setup, and I just had 2 new magna flow cats welded in, but no other smog stuff on it. I have gone over to the smog shop several times now, The truck will pass the 15mph treadmill test but fails on the 25mph (higher RPM) the guy says the NOx goes too high at the higher RPM, I have only really tried leaning the fuel mixture screws (stock quadrajet) to get it close. I have also run a bottle of the CRC guaranteed to pass through it. Is there anything I can do to get the emissions a little cleaner? I was thinking of messing with the timing? Any help appreciated thanks!
 
They usually check the timing, retarding the timing a few degrees will make it burn a little hotter. Do a tuneup, put 87 octane in it.. run the living piss outa it before you take it in.. If that carb is stock it might be the secondary rods are too rich so you might have to go into it and either change the jet or get a leaner(larger dia.) rod.
 
Sometimes high nox can be from running too lean causing combustion temps to be too high. The apt controls the a/f ratio at speed. You can adjust that a hair - but you have to be extremely careful - 1/8 of a turn is a lot.

http://www.73-87.com/7387garage/drivetrain/myqjet.htm take a look here.

Also, post up your results so we have a better idea what you're running.
 
Same boat man, I had the CCC on my '85 and I ended up just going TBI super cheaply and the refs barely looked twice at the truck when they gave me my smog sticker. Mines a DD, I ended up loving the TBI even though it was just intended to be a "for now" fix.
 
JoshHefnerX said:
Sometimes high nox can be from running too lean causing combustion temps to be too high. The apt controls the a/f ratio at speed. You can adjust that a hair - but you have to be extremely careful - 1/8 of a turn is a lot.

http://www.73-87.com/7387garage/drivetrain/myqjet.htm take a look here.

Also, post up your results so we have a better idea what you're running.
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Yea the combustion temps are too high (causing high NOx) what the guy said, the shop I have been going to is "Test Only" which means they don't do repairs, they can't really tell me anything other than the test results, I went to another shop and the guy there said to bring in the readout sheet and hopefully can give me some good advice on getting it to pass. Im going to try and richen the mixture screws a little and then play with the timing and see what happens, the reason I have it so lean is that the first couple of tries it was way too rich. Trying to find the middle ground with it. Im going in Friday and I will post what happens, Thanks!!
 
The mixture screws on the front won't have much effect when you're at speed. Once you're off the idle circuit they're really not being used. If you're lean on the road, you need to richen at that point - which you'd want to either adjust the apt, rods, or jets.
 
four50NCalif said:
Yea the combustion temps are too high (causing high NOx) what the guy said, the shop I have been going to is "Test Only" which means they don't do repairs, they can't really tell me anything other than the test results, I went to another shop and the guy there said to bring in the readout sheet and hopefully can give me some good advice on getting it to pass. Im going to try and richen the mixture screws a little and then play with the timing and see what happens, the reason I have it so lean is that the first couple of tries it was way too rich. Trying to find the middle ground with it. Im going in Friday and I will post what happens, Thanks!!
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If you want to have any chance on tuning the Q-jet to pass emissions, you'll need to do a bunch of reading. Especially once you start modifying the engine.

Those duals probably aren't helping you, yet another reason to not run them. Do you know if the cats are are getting to the right temp?
 
Cucvnut said:
Im not even sure true Duals are legal on that truck in ca,
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I don't see how they can be, it's a federal law that says you can't add or remove cats, CA is usually even worse, but I assume some places you can get an inspector to not look closely?

Regardless, the placement of converters is likely the reason the federal law was written as it was...in the wrong place, converters don't work right. When you change the exhaust, most people don't make an effort to figure out where the converter needs placed to most likely work properly, which is affected by things such as pipe diameter, volume, material used, etc.
 
I hated smog when I lived in CA, Im glad I moved to oregon, they have smog but less strict in my area and they dont smog k30,s anyways.
 
Cucvnut said:
Im not even sure true Duals are legal on that truck in ca,
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Yikes...gonna be waaay more to it than playing with the idle mixture screws (as @JoshHefnerX pointed out) and dumping fuel additives. :doah:

I don't see how you made it past the visual and even got to the sniffer portion. An '81 Blazer never came with true duals.

What cam does it have? What intake (more importantly, did it retain EGR)?
 
No I don't have EGR on it, the cam is a mild Comp 4x4, the intake is a JEGs aluminum, the headers and cat setup aren't legal but the smog tech is willing to overlook all that if it will pass the sniffer. Looks like I am about to fall down the rabbit hole in carb tuning, I have done all the work to the motor myself so far but haven't tried to do anything to the carb other than setting fast idle speed, warm idle speed and the mixture screws on the front. There is a video on YouTube about a guy doing a "lean drop" so I have tried that a couple times using a vacuum gauge. In that video he said that doing a lean drop is important to passing emissions.
 
NO is high because of a lean condition or too high a combustion temperature. EGR actively cools the combustion chamber.

So, given that you deleted EGR and need to cool things off in there (to below ~2500°F), your options are to run it richer and/or retard timing...of course, these will then cause your HC (unburned fuel) emission numbers to come up. I don't know if you'll be able to strike a passing balance.

The other possibility is that your cats aren't working like they're supposed to. With headers and duals they may not heat up enough to do their job.

four50NCalif said:
the smog tech is willing to overlook all that if it will pass the sniffer
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That's one brave (or stupid...or connected) dude...buy him a nice bottle of whisky if you end up passing. :deal:
 
It sounds like you are fixated on idle adjustments. Those aren't going to fix 25MPH treadmill numbers. The problem is from a combination of changes, and the solution is going to be more in-depth than turning the idle mix screws in or out and watching vacuum. As mentioned, timing may help, but if you have to richen the mixture up, under load you are talking needles and seats, not idle mix screws.

If you are running the original carb, removal of EGR WILL make it run lean at part throttle cruise. EGR is inert, so when the EGR valve is active, it is dumping inert gas into the cylinders. That displaces oxygen, which means you need less fuel, thus the carb is calibrated to provide less fuel under that specific condition (which is light throttle cruise). If you remove the EGR, the carb is providing the same amount of fuel as before, but there is more oxygen to burn...which results in a lean condition.

You'll probably even feel a lean surge driving at low speed on flat ground, with light throttle. I eliminated the lean surge by running either richer jets or needles, but I didn't have to pass sniffer either. It ran better, so I didn't dig into it anymore. APT and all that probably factors in, I went fuel injected before having to delve that far into the Q-jet.
 
dyeager535 said:
It sounds like you are fixated on idle adjustments. Those aren't going to fix 25MPH treadmill numbers. The problem is from a combination of changes, and the solution is going to be more in-depth than turning the idle mix screws in or out and watching vacuum. As mentioned, timing may help, but if you have to richen the mixture up, under load you are talking needles and seats, not idle mix screws.

If you are running the original carb, removal of EGR WILL make it run lean at part throttle cruise. EGR is inert, so when the EGR valve is active, it is dumping inert gas into the cylinders. That displaces oxygen, which means you need less fuel, thus the carb is calibrated to provide less fuel under that specific condition (which is light throttle cruise). If you remove the EGR, the carb is providing the same amount of fuel as before, but there is more oxygen to burn...which results in a lean condition.

You'll probably even feel a lean surge driving at low speed on flat ground, with light throttle. I eliminated the lean surge by running either richer jets or needles, but I didn't have to pass sniffer either. It ran better, so I didn't dig into it anymore. APT and all that probably factors in, I went fuel injected before having to delve that far into the Q-jet.
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I (Used) to be a Cali smog inspector (years ago so I might not be up on all the new rules) but, dyeager is correct. Carb is tuned for egr. EGR is designed to reduce NOX. You may get it to Pass NOX with internal carb tuning but you will probably fail CO and HC. That's one reason they came up with the treadmill.
The Q'jet is actually a very good carb when you have someone that knows how to tune one, (most people see it as a black art).

If that vehicle was never offered with dual exhaust or it could not be ordered then it is illegal.
If it came with EGR, it must retain EGR.
If it came with a smog pump it must retain ALL smog pump equipment.
All internal and external modifications to any emissions system must have a CARB exemption sticker.
Your guy is not doing you any favors by overlooking the illegalities of your vehicle.
1. It is illegal for you to remove or change any smog related equipment unless the changes have an exemption order.
2. There are hefty fines for doing so and the smog police will be looking for vehicles like that. Ask me how I know this.
3. Your guy can lose his license and possibly go to smog jail for passing it without proper equipment.
4. No reputable shop will do any such modifications.
5. The shop that installed the Duals can be fined for doing so.

There used to be an exemption you could apply for if vehicles of a certain age could not be brought into regulation without a vast outlay of money. I do not know if this is still the case or, what year / vehicle age it applied to.

If you take it to a proper repair facility they must by law complete the smog test (they cannot tell you they won't complete the smog test). You can have them give you a detailed estimate as to how much it will cost to repair it.

Remember, any time you take it for the test all results are data linked to CARB for that vehicle.

This information is only accurate for the locality and years I was an inspector. Check all you local emissions laws before making any other changes.
 
Back when I had my factory 305, I had the same issue (I've since installed a 5.3 Vortec). Anyhow, I had success by running the truck for 30 minutes or so to get it at normal running temperature with a near empty fuel tank. Right before I drove to the emission shop for an inspection, I'd put 6 to 8 gallons of Ethanol in the fuel tank. That sh*t runs really clean. After I passed the inspection I'd drive around town to finish burning the Ethanol out of the tank then fill up with normal gas. Ethanol will not hurt any part of your fuel system by only being in it for an hour or two.
 
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