A friend has a 86 Ramcharger with a 318. It keeps back firing when ever he lets off the gas. A mechanic told him that the back fire valve is not working. At one time it had dual exhaust put on it and some things had gotten disconnected. My friend bought it this way. The rig is spotless inside and out so he wants to keep it. It only has 89,000 miles on it.

What in the world is a Back fire valve and how does one fix it? Looking at a book, it shows it in picture and it looks like it is all hooked up correctly. Any ideas how to fix it?

Montana T

 

They are replaced as an assembly. It's part of the emissions system and air pump system.

THEORY
The diverter valve, prevents backfire in the exhaust system during sudden deceleration.
When the throttle is suddenly closed at the beginning of deceleration, the air/fuel mixture becomes too rich to burn. When the mixture reaches the exhaust area and combines with the injector air, it becomes burnable, and the next firing of the engine will ignite the mixture. When the diverter valve senses this sudden increase in intake manifold vacuum, the valve opens, allowing air to pass from the air pump, through the valve and silencer, and to the atmosphere.
A pressure relief valve, integral with the diverter valve, controls system pressure by diverting excessive pump output at high engine speeds to the atmosphere through the silencer.


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