Question about Chevrolet Astro

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1999 Chevy astro van 4.3 2 wheel drive. Its blowing thick black smoke, 1 year ago the distributer cap wires were / sparkplugs were changed because of a rough idle at the dealers. It solved the problem but its back and worse. So i changed all 6 plugs , properly gapped 60 guaged , did nothing. Im not totally a nieve home mechanic dude but something is very interesting . The 3 right bank plugs i pulled out are heavily grimed with black sout but the 3 left bank plugs are clean and changed them all anyway. My mechanic friends says its the wires.

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6 cylinder 4.3 Chevy motors are notorious for this. I actually look for these vehicles to buy, because people think there is something severely wrong with them and they sell them cheap and it's really an easy fix. What's happening is, as these 4.3 engines get up in mileage, at the back of the cylinder head,right on top of the side with the "sooty" spark plugs there is what is called an oil return.It's simply a hole through the head. Once oil is pumped up to the top of the head,(under the valve covers) due to the angle that the engine sits at leaning toward the rear, the oil runs to the back of the head and runs through this hole "returning" to the oil pan, where it is picked up by the pump to start the cycle again. Well, on the 4.3 GM engine one of these oil returns becomes clogged with sludge and "gook" not allowing the oil to return to the oil pan. So it sits on top of the cylinder head when you shut off your engine. As the car sits, this build up of oil slowly runs through this clogged oil return,pooling up on the back of the valves where it seeps through your worn valve seats, filling the cylinder (combustion chamber). Where it sits until you start your car, when poof clouds of smoke from all of that oil burning of upon ignition. Before starting this procedure buy new valve cover gasket and RTV cement.
I don't know how mechanically inclined you are, but to solve this all you have to do is;

  1. Disconnect negative battery cable
  2. label each spark plug wire and remove them from each cylinder.Leave them connected to the distributor cap and lay them over the top of the engine out of your way.
  3. Carefully remove any other hoses that are in your way to remove the valve cover. I can't think of anything else that's in your way off the top of my head. All make and models are different and GM put that motor in a lot of different vehicles. If you think you'll forget where they go label them.
  4. Remove valve cover bolts and pull valve cover off. It will resist a little bit because it's glued down.
  5. Find oil return in the rear of the cylinder head.Using a small pick like tool remove"****" in the oil return(don't worry if "****" falls into cylinder, but try to avoid it)
  6. clean old gasket from valve cover and cylinder head with scraper or razor blade.
  7. replace gasket using rtv cement (don't over due it)
  8. reassemble valve cover
  9. reconnect spark plug wires
  10. reconnect battery
Vehicle may smoke on first couple of restarts. Good luck !!

Posted on May 22, 2011

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These are known for distributor caps and rotors going bad,also if this is a vortec motor they also have a problem with the injectors leaking in the intake manifold causing pooling of fuel and a rich running condition,on the side with the leaking injectors.check for any codes and take a look at the map sensor.these should be checked out.

Posted on May 22, 2011


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