What is a plenum and what are poppet valves?

[raedeus]

Okay, I'm no expert but I'm told I may have a leaking poppet valve on my 1991 s10 Blazer (4.3L TBI, not Vortec). Apparently it's leaking into the plenum. So, is this part of the throttle body or is it inside the manifold? My Haynes manual has no mention of either of these parts throughout the whole book. Anyway, I was thinking about buying a rebuild kit for the whole throttle body/meter body to fix a starting problem that this leaking poppet valve is supposedly causing. Vehicle idles rough right at start up but I give it gas and it smooths out and then runs and idles perfectly fine. Anyway, I have heard of a cleaner I could run through my gas. Anyone know what kind of cleaner I could try before sticking parts into this beast? I know the Vortecs or motors with CPI have these poppet valves but I'm not sure about mine. Thanks for any help!

[sreve]

alot of times cold start problems go back to state of tune. ie: plugs ,wires cap, rotor, timing. from what you describe i wonder if the thottle body is clogged with crap and just needs a cleaning.

[mustangmike351c]

I'v had to replace the spider in alot of those for the same things your talking about. the injectors, regulator everythings inside the plenum.

[silicon212]

Originally Posted by mustangmike351c

I'v had to replace the spider in alot of those for the same things your talking about. the injectors, regulator everythings inside the plenum.

He's asking what the plenum is. To answer that question, the plenum is the area of the intake directly below or behind the throttle body. This is the area where all individual runners branch off to their respective cylinders.

Also, his car is TBI, which is a veritable carburetor setup, but with electronically-controlled injectors in place of the float/venturi of a standard carb.

A poppet valve is what's used for the cylinders - the intake and exhaust valves are poppet valves. A leaky intake valve can definitely leak into the plenum, but usually intake valves don't leak or get burned under normal use.

[mustangmike351c]

Originally Posted by silicon212

He's asking what the plenum is. To answer that question, the plenum is the area of the intake directly below or behind the throttle body. This is the area where all individual runners branch off to their respective cylinders.

Also, his car is TBI, which is a veritable carburetor setup, but with electronically-controlled injectors in place of the float/venturi of a standard carb.

A poppet valve is what's used for the cylinders - the intake and exhaust valves are poppet valves. A leaky intake valve can definitely leak into the plenum, but usually intake valves don't leak or get burned under normal use.

the poppet valve they are talking about is the injector its self. if it was the intake or exhaust valve they would just call it the intake or exhaust valve. what I was getting at was he needs new injectors to fix the problem

[dewaynep]

This is a '91 with TBI, not csfi. No spider or poppet valves in the intake plenum. There isn't even, technically, a plenum. There is a TBI unit with 2 injectors attached to an intake manifold (that's why there is no mention of a plenum or poppets in your manual). Yes, you could get either: 2 new/reman'd TBI injectors, a whole new TBI unit or rebuild the injectors yourself. Just a quick check at the "zone" shows new TBI injectors available for about $50.00 each, or the rebuild kit at $35/each. Your call.