I have a 99 Expedition and I have replaced wires, plugs, and flushed the injectors. I have a back fire between 45 and 50 MPH. The truck feels like it is starving for gas. It seems to now start it at 60 also. When I step on the gas hard it spudders hard then seems to get gas. HELP !!!!!

 

Have you replaced the fuel filter? or get the exhaust check?

 

Done all this!! someone said sounds like TQ convertor in transmission and it's not a backfire but the transmission Tq convertor making the noise. Sound familar?

 

Yea, had a Buick that did something like that. It ran fine but when you got on the freeway the car would start bucking/ spuddering. What happens if you drive it in 2nd gear?

 

More than likely you have a coil on plug going out. Is the check engine light coming on.