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Check Valve pic in an 87 351; "...If you have an exhaust leak, it may not be the manifold. Follow the hose from the smog pump to the back of the intake, it will go into a checkvalve on the crossover tube between the heads. The top of the checkvalve was rotted off inside the hose and created the leak there..."
Source: by broncoRPG at SuperMotors.net
Crossover Tube, Diverter & Check Valve Removal in an 88 5.0; "... took my upper plenum off ( I love that rear most bolt that won't allow a socket wrench on it), and found and removed the crossover tube. It has two 1/2" bolts that hold it onto either side of the motor, at the heads. It had alot of red colored carbon buildup, but no rust. I am replacing the valve eventhough it looks good, and hopefully I can keep the pipe, after cleaning it out, as long as the pipe doesn't break after removing the valve. The valve bolt is a 32 mm..."
Source: by Daves 88'
Crossover Tube, Diverter & Check Valve; "...The check valves run around $20.00 at any auto parts chain and they're made of cheap material so it's unlikley the tube itself will rust thru because the material is very thick...
Air Bypass Valve" is.........that valve should be off to the passenger side firewall behind the FI plenum directly above the CAT tube area and the vacuum line runs up front and converges into a four way vacuum line junction piece which heads over to the EGR solenoids on the fender liner behind the battery area............that's how mine is set up but m ine is an 86
If you look closely you'll see the chek valve and C/O tube is pipe threaded, use some anti-seize and don't over tighten and when putting the valve on the tube, you don't need a gasket for the CO tube ends but rather just use some bearing grease which melts and forms a nice gasket seal; this is a tip from Steve83-gaskets burn off and go away after a while and you're back with another vacuum leak etc..."
Source: by JKossarides ("The Bronco", Jean)
Crossover Tube, Diverter & Check Valves & Hoses Location Diagram in a 5.8
Secondary Air Injection system consists of a belt-driven Air Pump, single or dual AIR Diverter valve(s), an AIR Bypass valve, and AIR Bypass solenoids, air silencer/filter, Powertrain Control Module and connecting wires and vacuum hoses. The Belt-Driven Secondary Air Injection system provides either upstream/bypass air or upstream/downstream/bypass air. The number of these system configurations vary significantly with AIR Bypass and AIR Diverter valve combinations (Figure 179).
1. The PCM requires ECT, IAT and rpm inputs to initiate Secondary Air Injection operation.
2. The PCM provides one or more signals that enable one or more AIR Bypass solenoids.
3. The AIR Bypass solenoids control one or more AIR Bypass valves and/or AIR Bypass Diverter Valves in order to route secondary air depending upon the specific configuration.
4. The belt-driven Air Pump is operational any time the engine is running.
The 2ndry air system is known to fail in a wide variety of ways. The check valves that prevent hot exhaust from entering the rubber hoses age, rust, leak, & crack open melting the plastic TAB & TAD valves, creating exhaust leaks that can damage other components, raising exhaust oxygen levels (setting lean codes or rich adaptive limit codes), and making rattling noises. The hard steel tubing between the exhaust & the check valve can rust or crack (especially the infamous "crossover tube" on the backs of V8 heads). The vacuum controls leak (including the "coffee can" reservoir on the R wheelwell), get misrouted during other repairs, or the diaphragms rupture. The electronics that control the vacuum controls can fail electrically or mechanically, or the wires can be damaged. But all of these failures are either A) relatively cheap & easy to repair, or B) cheap & easy to prevent with normal inspection & maintenance.
Source: by Ford via Steve83 (Steve, That dirty old truck) at SuperMotors.net
