Re: 94 F350 w/557 EFI....
The early efi systems are known as a "speed density" system and are not very adjustable or adaptable to any engine modifications, later on the system changed to a "MAF" mass air flow system, from 1996 on.
Unfortunately you will need to update the engine bay to 96 on spec's, that is the complete front wiring loume, computer, MAF, o2 and everything else that plugs in including some of the intake pieces from the air box back to the intake manifold.
Most of these parts will have to be sourced from a junked F series, and if you do you must make a note of all the vehicle details that the parts came from, ie: build date, if its a super cab etc etc, in case you need to replace any faulty parts. (eg: there are 9 different o2 sensors for a efi 460)
Its one big pain in the ass, but you need to do it if you want it to run spot on as the later system is fully adjustable.
I have just been through this whole experience with a 95 F series efi 460.
Speed Costs Money
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