Hi, I have a 1992 e350 van that is having problems. At speed, it had a hesitating miss when climbing or accelerating and there is a metallic clicking sound associated with it coming from under the doghouse. It wasn't the plugs or wires, and wasn't the fuel filter. What else can it be? A friend has one that's doing the same thing.. Thanks very much!

 

Those year vehicles had what was called TAD (thermactor air divert) and TAB (thermactor air by pass) Solenoids/valves. The idea was to direct air from an air pump to the exhaust manifold when the engine was cold to complete burning of the exhaust. When the system reached operating temperature air was now diverted to the converter to help clean the exhaust. In the system were various check valves to prevent backfire from ruining the air pump.
I believe with your engine either one of those check valves has either rusted through or burned through and what you hear is the exhaust going through the piping. The pipes at the rear of the engine also can rust through and leak exhaust. The system was good when it worked and the only problem was the rusted or burned through check valves. Once replaced they lasted a long time and gave no other trouble.
If you can, remove the doghouse cover over the engine inside and you will have no trouble seeing where the exhaust leak is coming from.