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1984 Chevrolet Blazer:
Runs Rough Cold, Possible Carburetor Icing

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Alex Steele
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seen in Truck Trend

Question:

 

My '84 Chevy Blazer runs rough under certain conditions; always below 45 degrees and usually after a rain. (There's no problem in warm weather.) It seems like it's not running on all cylinders, the engine bogs down and sometimes it stalls. Usually, this happens about 15 minutes into a highway trip.

 

My mechanic has ruled out the carburetor. He's replaced the distributor cap, rotor, wires, plugs, coil and the EGR valve, none of which has helped. My cousin, a mechanic in Michigan, suggests it could be carburetor icing.

 

Answer:

 

Carburetor icing is a definite possibility. Every modern carbureted engine has a method of warming intake air during colder ambient temperatures. In some cases, ice can build up in the throat of your carburetor even though the outside air is significantly above 32 degrees F. It's like the wind chill factor you hear on the weather forecast every day. The faster the air moves, the colder it gets. Icing can limit the amount of air entering the engine. This changes the air/fuel ratio, giving you symptoms like those you describe. Even without icing, cold air will hinder the combustion process and cause drivability problems.

 

The system that's designed to deal with this condition has various names, depending on the manufacturer, but we'll just use "thermostatic air cleaner." This term is pretty universal. When your engine is cold, the system uses vacuum to open a little door, diverting warm air from the exhaust manifold to heat your carburetor. As the engine warms up, the thermal switch releases the door to allow fresh, cooler air from the main intake to enter the air cleaner, carburetor and engine. Here are some things your mechanic should look for:
1.) Make sure that the tube from the exhaust manifold to the air cleaner is in place and properly attached.
2.) Check all vacuum hoses. Make sure that they are attached and not kinked, cracked or cut.
3.) Check for vacuum in and out of the thermal switch when cold. Then make sure it gets to the vacuum diaphragm that opens the little door.
4.) If the door remains open. Check the diaphragm for leaks.

 

Now, if you and your mechanic have gone over the entire system and everything works properly, start looking elsewhere. You've eliminated this system as a possible cause of your drivability problem, and you haven't wasted any money.

www.realworldautomotive.com

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Chevrolet | Carburetor | Misfires | Idles Rough | Stalls
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Comments:

techhelp2
15 Oct 2014, 18:29
Anything is possible if you have the tools and the know how. The V8 would be one that would fit, I'm sure there will be lots of fabrication to make it fit. The engine and the transmission should be used together because of gear ratios and converter lock up system. You would need to find out if the computer would be able to be programmed for the V8 and transmission; if not then a computer would have to be found to fit the program of the engine and transmission. Then you might have to change the wire harness to fit all the new sensors and computer. It is a lot of work and a big project but with the knowledge and tools it can be done. Best thing to do is to stick with the same engine and you will get many more problem free miles and less headaches.
Nautica
23 Jul 2014, 07:25
Hi guys, I have a '97 Astro 4.3L with 216K, since I already have some trouble with this engine due to high mileage, I've been thinking about a swap to a v8. My questions are, what kind of engine I should look for and what about the transmission, can I use the one that I have now? or I'm going to need the one that the v8 uses. I've been reading a lot about the computer that they can be reprogrammed and modify the wiring harness, sorry lots of questions, any help will be great, thank you.

 

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