Hi
I've got a 94 Blazer with the CPI Vortec motor, runs and drives fine, except at idle its real choppy and rough. I know the common problems with these trucks is the fuel pressure regulator and the fuel lines, is there any way to tell if its the actual fuel injector itself or if its one of the other two possibilites?
What should I be looking for to figure this out? Thanks,
-Chris

 

If the injector were acting up, it would exhibit drivability concerns at idle as well as up in the rpm range.

I suspect you have an internal fuel leak from a leaking fuel pressure regulator or a leaking o-ring/line. I would check the fuel pressure via the fuel pressure test port on the fuel supply line at the back of the intake near the brake booster. You should see 55-60psi at the test port with the key on. If, after turning the key off, you notice a steady drop in the fuel pressure, there is a fuel leak internal to the plenum. To diagnose further, you can pull off the MTV (round plastic cover under the black plastic w/ orange 'VORTEC') and look down into the intake. You will be looking for pools of fuel. If you cannot get a good view, you may have to pull off the upper plenum. With the upper plenum off, look for any leaks on the internal fuel lines and the spider itself. The fuel pump can be activated with the upper plenum off to look for leaks under pressure.

When was the last time that the engine was tuned up? New plugs, wires, cap, & rotor? It is possible that a rough idle can be caused by fouled plugs...

Hope this helps!