I took the Blazer to the shop today. Mechanic said the vacuum leak is from the seal where the spider goes thru the upper intake (plenum). He told me needs to remove the upper intake and replace the entire gasket set. Does this sound right?

 

There is only one Oring around where the spider goes threw the plenum ,and only one gasket between the plenum and the intake manifold. But yes this can cause a major vacuum leak and cause all kinds of problems

 

I have a 1996 2 dr BLazer, and this past weekend I pulled the plastic plenum off to look at my fuel injection spider, Fuel pressure regulator and what ever else is in there. I was smelling raw gas occassionally. All of the parts in the fuel system looked ok, but I noticed the bolts that are located closest to the distributor, were loose. Evidence of a vacuum leak showed where the gasket had lifted from the aluminum lower manifold. I went to Oreilly and bought the FelPro silicone set of three gaskets for 20 dollars.

There is a large continuous gasket for the bottom of the plastic upper plenum, one that is an obrounded shape to seal the fuel injection spider opening, and one for the seal between the throttle body and the plastic plenum.
I think alldata says it takes about 3 hours, and is a relatively easy job.

 

Yes their is an gasket on the bottem of the plenum also, but on the newer models it is just on continous gasket. And yes I stand corrected their is actully three because their is a small 90 on the back right on top of the plenum and that little oring/gasket is hard to find.