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Emissions tricks?

Trying to get my 77’ Chevy pickup through emissions. The motor has 300,000+ miles on it, so I don’t want to make any significant repairs to a motor that wont last, but I am failing emissions. The first emissions trip, it blew 719 in hydrocarbons after the precondition, with the standard being 250. At the same time, my carbon monoxide was only 0.02 with the standard being 2.00. Since the truck sat for 4 months, I drove it 120 miles down the freeway to clean it out. I also tried to lean the carb, but it has only one adjustment screw. I turned the one screw in about a half turn. Back to emissions. Now my hydrocarbons are 632 and my carbon monoxide are 0.01. It seems strange that my carbon monoxide is so low while my hydrocarbons are so high. My temporary tag expires after tomorrow, and I cant get anymore so I need to pass tomorrow. Is this a simple fix, or are there any tricks that actually work? Maybe mixing some ethanol with my gas?

You might be burning oil - have you changed it recently, trying an oil for high-mile vehicles?

Before I took it to emissions, it was about 1 quart low. I topped it off with Lucas.
Last year I did have to change the oil to pass, but the currant oil is not very dirty.

Would using half E85 and half gasoline work?

what about this “guaranteed to pass” fuel additive at wal-mart?

It can’t hurt…I’d still think about changing the oil, if this is a must-have truck…no ‘guarantee’, though!

High hydrocarbons without high carbon monoxide generally means a misfiring cylinder. That allows unburned fuel into the exhaust, and unburned air as well. Unburned fuel equals high hydrocarbons, unburned air lowers carbon monoxide.

Make sure the spark plugs, plug wires, distributor cap and rotor are in good shape.

I’ll check the entire ignition system tomorrow. I am also going to try the De-natured alcohol trick. I’ll re-post tomorrow with the results.

Wow, tell me what state still makes you test a '77 truck so I can make sure not to move there!

Which engine is it? I have a '76 with the 250 and it has a catalytic converter and an EGR valve and that’s pretty much it emissions-wise. Doing a full-tune up and changing the oil (maybe with a little bit higher viscosity than normal) is pretty much all you can do, other than maybe cleaning the EGR. Be sure you are doing the tune up as per the factory specs-- if the thing has just been tuned by ear it’ll probably run better, but won’t pass smog.

I would also say at this mileage you had probably ought to do a compression test before you put too much money and effort into it because if you’ve got a dead cylinder or just generally low compression, there’s no way in heck you’re going to pass and it’s time to drive it to the nearest state line and put a “For Sale-- Cheap!” sign on it.

Oh, also just to emphasize, when you’re doing your tune-up timing is especially important. One of the classic emissions test tricks is to advance the timing a few degrees, which will result in some knocking under load but more thorough combustion.

Great tips. I’d pull the plugs and hit them with a wire brush and regap them, put in fresh 20w-50, change your PCV valve, take a look at your distributor cap and rotor (after that many miles, you may well have a weak coil, and any extra resistance between it and the plugs is just going to make things worse), and advance your timing a degree or two, as GreasyJack suggested.

As he also said, before you dip in to real money, check out the compression!

Adjust your CO up to 1.75,your CO is so low your are lean missfiring.putting your HC high,now you may have a vacuum leak causing your low CO and adjusting the carb only covers up finding why your CO is so low.

If this vehicle has a cat you have to take you sample upstream of the cat.

Now finding a shop with a gas analyzer will be a problem.

I suppose I need to explain the situation a little better. The truck has the 250 inline six. The truck was sitting for 3 months prior. The truck will have a new crate motor by this summer, so I just need this to pass this one time. I live in AZ greasyjack, which is now the hardest state to drive in. If I lapse on my insurance for even a day, my license and registration is suspended immediately. Not to mention the fact that driving on a suspended license will get your car impounded, and, it costs 50 bucks to reinstate your license and the same to reinstate your registration. That doesn’t even include the six months of paid insurance you are required to have just to get your license. Can anyone say crooked as sh%t?
I need a sure fire trick to pass, and I need to do it today. Anyone tried de-natured alcohol or E85?

There is nothing sure-fire. Together, the things suggested could help. The engine has high HC (HydroCarbons) from unburned fuel. One very useful tool, to determine if there is a vacuum leak, is a vacuum gauge. Yeah, I know, it doesn’t sound very glamorous, but, it’s utility is what counts. Here are the indications to look for:
Scroll down and click on each green Scenario.

Those sound like good tips to me too. What about using high mileage oil? If the OP is burning oil, it might help.

Just pulled a plug. It has some white soot on it and smells like acetone/bad gas. DOes this indicate something?

White deposits and a very light colored ceramic insulator indicates it’s running too lean. The smell is normal. As Oldschool said it’s likely lean misfiring. Besides a vacuum leak it could be gunk in the carburetor reducing fuel delivery. Gunk that built up from 3 months of sitting.

just checked the timing, it appears to be way advanced. I might have the timing light on the wrong plug though. Anyone know where to find firing order and correct timing for a 77 chevy 250ci?

Here you go:,26200242/shopping/specsSelect.htm
This site, also, has ignition timing specs, and other nifty stuff.

Well I’ve heard stories of there being shops that have a certain price to make a vehicle pass… if you know what I mean. (Something I don’t necessarily condone…)

The firing order is on the intake manifold, up front right near the valve cover. The timing spec and procedure (you have to pull the advance hose) and some other tune up information should be on a sticker that’s right on the front of the engine compartment, to the right of where the hood latch is.

If even with the advance tube out the timing is still very advanced, I might say that that might be all your problem is.