A few days ago I let a friend drive he put diesel fuel in instead of premium I was told to pour sea foam in tank and let it flush out since then car has stopped on me the service engine light came on and speedometer won't work
Speedometer not working is due to the vehicle speed sensor. With the 4.6 engine, this is located on the transaxle at the rear of the engine. On the 4.9, it's on the right front of the engine.
You need to get all of the diesel out of the fuel system before flushing. Drop the tank and drain it, disconnect the fuel line before the fuel filter and hot wire the fuel pump. Something like that. THEN you can use the fuel system cleaner to clean out the injectors.