My 92 Explorer is backfiring a lot. It happens at low rpms (1800-2000), usually around 35-50 mph, and it will backfire several times. It is not unusual for it to backfire rapidly 5 times or more. What could it be -- plugs, wires, vaccuum leak, O2 sensors? Any help is appreciated. Thanks!

Stock exhaust or aftermarket?

stock exhaust

Timing...Plugs, wires,etc. will make it miss, but not backfire..Take it into the shop, sounds like it's time for a chain..How many miles on it?

137,000 miles on it. The backfire sounds like it is coming from under the hood, not the exhaust, if that makes a difference.

Quote from Haynes Manual..Trouble shooting...Engine Backfires..1 Emissions system not functioning properly 2 Fault in the fuel or electrical system 3 Faulty secondary ignition system 4 Fuel Injection system in need of adjustment or worn Excessively 5 Vacuum leak at the throttle body, intake maniford, or vacuum hose 6 Valves sticking 7 Crossed wires...

Can you hear a knocking sound coming from the front of the engine? The timing chain was bad on my Dakota and was causing a knocking sound and backfiring. Changed it and runs much better now. (my dad owns it now)