Neko
Pit Crew Chief
Aug 29, 2004, 3:21 PM
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86 Dodge Van Exhaust Fireworks
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Q: We have a 1986 Dodge Ram 150 Conversion van with approximately 68,000 miles on it. For quite some time we have had a problem with the van back firing and stalling at intersections. Our mechanic has worked on it and can’t seem to find the problem. The carburetor has been rebuilt twice. The choke adjusted, replacement exhaust tube & emissions valve, new spark plugs & wires, PCV valve and gas filter.
The back firing is the main problem and occurs whenever you accelerate rapidly and then let off the gas. One of the last times it back fired, it blew the muffler apart.
This is very frustrating and expensive. Any help you can give us would be greatly appreciated.
A: From your description it is likely that there is a problem with the air injection system. The air injection system provides additional oxygen to the exhaust to assist in burning remaining gas and reduce pollutants. But there is a time when there can be no air injection occurring, that is during deceleration.
When you let off the gas pedal of your vehicle to slow down quickly, for a brief moment there is not enough oxygen available to burn the gas in the engine. This unburned fuel is dumped into the exhaust. Here’s where it can get exciting! If by chance, additional oxygen is introduced in the exhaust with the unburned fuel, kapow! The unburned fuel will ignite, alerting all innocent bystanders of your presence. The intensity of the explosion will vary from a mild bubbling in the exhaust to an impressive display that will illuminate the whole underside of your vehicle as it blows the muffler apart. As the kids would say, “Way-cool!”
The component responsible for preventing this untimely explosion is called a diverter valve, makes sense doesn’t it? The diverter valve uses a vacuum signal from the engine to determine when a sudden deceleration is occurring. At which point it will prevent the air injection system from pumping oxygen into the exhaust. Then it will allow the air injection
system to return to normal operation.
Have your technician inspect the diverter valve, vacuum hoses to it and any controls such as electric switches that are responsible in controlling the system. I’m sure he/she will find the cause of your light show in that area.
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