Chevrolet Repair: Rough 91 S-10 Blazer Fuel Injected 4.3 4x4, fuel pressure regulator, throttle body injection

Question
I have a 91 S-10 Blazer Fuel Injected 4.3 that is running very rough, at idles it revs up then back down, it bogs down and sputters when accelerating, backfires intermittantly while driving, and vibrates pretty badly.  It smells like it may be running pretty rich.  I changed my air filter and it smeeled like oil and fuel and was a little black.  It is progressively getting worse.  What are your reccomendations and where should I start?

Answer
Hello Kevin,
A good general tuneup...plugs, wires, cap, rotor if they are orriginal.

Then test the fuel pressure.

If that has central point fuel injection, you may need to remove the top plenum of the intake manifold, and check the poppet lines. If one of them is leaking, it will pour raw fuel into that cylinder.
If it is throttle body injection, check the throttle body to see if it is leaking down inside.

There is also a fuel pressure regulator that has a vacuum hose connected to it. Remove the hose, and see if there is gasoline in it. A ruptured diaphragm will allow it to suck gas there.

Van