What would cause a mustang gt 5L to miss and backfire?

Answer 1

Incorrect timeing, spark plug wires hooked up incorrectly at the plugs or the distributor. List year and if the engine is HO or not for firing order. It could also be the ignition control module (the little gray box with a wiring harness plug on the front of the distributor). And most people don't know this, but when timing a 5.0L HO motor, there's a little thing you unplug before you time it. This little thing looks like a fuse, and you'll find it on those wires that come from the ignition control module. It's small and gray or black in color. When you time a 5.0L HO and that thing is plugged in, it will make the timing look like it is at around 18 degrees. However, if you unplug it, it will be around 12 or 13 (or should be). You need to time it with the fuse like plug out, and time it to around 12 or 13 degrees. After you are done, plug that thing in. I wish I knew what that thing is called. == That fuse-like thing is called the SPOUT Connector and when the Ignition Module goes bad, most of the time, the car won't start. If the backfiring is in the intake, the motor is running lean or the timing is very retarded. try running premium gas