Klondike

I think that's what they are called?! I'm talking about those little can valves that are in the tubes connected to the exhaust manifolds. I've searched and can't really find any info on how they work or how you can tell if they don't. My LT4 doesn't have an EGR but has two of those things on a pipe that runs behind the intake manifold to each exhaust manifold. One side of that pipe connects between the passenger side exhaust manifold and the rear of the intake manifold with nothing between the two ends. I can't find any pictures of the manifold passages involved with that tube, so I have no clue what is going on as far as air flow in that pipe. If it connects to the under side lifter valley, what keeps it from sucking oil into the exhaust or putting exhaust into the engine? Any diagrams or links to an explanation of how these valves and pipes work would be appreciated. It just but it bugs me to not know how something works.

zr1fred

"Backfire valves" in the smog pump lines. They allow pumped air into the exhaust, but stops the exhaust getting into the air pump lines. Same for all years.

LT4GS96

If I am understanding you correctly, there are two of these valves (one for each exhaust manifold). if you follow the hoses back to the front of the car (driver side) you'll find an air pump near the turning signal assembly. During cold starts, the air pump pushes air through the valves and into the exhaust manifolds to fool the O2 sensors resulting in the engine running more smoothly. If there hasn't been any modifications, a faulty one will throw a code. So if you have no code, no worries. If you do, they are inexpensive and not terribly difficult to replace. You can get the stock black painted ones on rock auto.

Klondike

On my LT4, both of the valves are in the driver side line. The passenger side has a pipe that goes from the exhaust manifold to the rear of the intake manifold (no valve on this side) and then junctions into the pipe from the driver side. I don't understand what keeps the exhaust from pressurizing that pipe on the passenger side, but I don't know where that pipe really goes inside the intake manifold. I've never had it off, so I don't know if it is blocked off at the manifold and that junction pipe is just a support bracket, or if there is some kind of an orifice or valve inside the manifold on that side. It just looks odd to me and I'm trying to understand how it works on the passenger side.

ColaBear

@Klondike,
The pipe from the passenger side goes from the exhaust manifold to the intake manifold (off to the passenger side of the back of the manifold and below the EGR valve on the LT1) so your LT4 should just have a blank area machined out since you have no ERG valve. There should be two bolts and a gasket on the back of the intake manifold with a hole in the center so the pipe feeds into the intake. The driver side has the check valve and this pipe mates up to pipe coming from the passenger side.

Per the 96 service manual, these two pipers are called the “secondary air injection pipe”.

Don’t know if this helps or not.

LT4GS96

Mine (very certain this portion is stock) runs like this: air pump (directly under where the driver headlight is when hood is closed) has a hose coming out of it that leads to a T between the engine and wheel well. Hose leading back to the front of the car from the T connects to valve which connects to pipe that threads into the exhaust manifold. Hose leading to the back of the engine compartment (between firewall and engine) goes to identical valve and then into a pipe. The pipe T's a few inches after the valve with one end bolting to the intake manifold and the other going to the exhaust manifold. I replaced both of mine about a year ago because one of them was causing a code.