I have a 95 Blazer 4.3L which intermittently runs rough and puts out black smoke and soot. This seems to happen more when cold but does not disappear completely when hot.

Changed plugs/wires/cap/rotor, oxygen sensor, and MAP sensor. Checked intake manifold gasket for signs of failure but it looks fine. Some suggestions made to me are TPS sensor or coolant temp sensor.

Any ideas you guys may have would be appreciated. Thanks.

 

Black smoke is generally fuel. White is coolant, blue is oil.

I'd bet you have a leak under the plenum dumping excess fuel into your cylinders - either on the passenger side (fuel pressure regulator) or driver's side (fuel pressure and return lines, aka 'nut kit').

Check your fuel pressure. Then pull the Vortec cover and pull the round thing beneath it (the IMTV). Be gentle; there's an o-ring you need to reinstall the valve. A little WD40 around the outside and some gentle twisting will break it loose so you can remove it.

Look inside the hole with a flashlight - anywhere that's gold looking, or washed, means a fuel leak. Black, gooky carbon is normal.

 

I had the same problem with mine. Your fuel filter might be clogged up. The guy who took it off my Blazer said he couldn't hardly blow through it at all. Put a new one on and it was running like new for around 35$ or so. That might be the problem with yours.

 

I had the intake manifold off to check the gasket. Everything looked pretty dark. You could see that some center parts were gold colored metal, but no obvious signs of washing. I will inspect closer in the week to come.

As for the fuel filter. I have been dreading changing the thing.

I will check both of these things asap and post an update. Thanks for the quick responses.

 

Hit both flare nuts on the fuel filter generously and often with penetrating oil, like PB Blaster, for a few days before you change it. Tap on it with something metal after you've sprayed (helps the capillary action). Use proper flare nut wrenches to avoid stripping the nuts. Mine came off pretty easily even though it was the factory part.