You can do downward compatible changes to OBD1.5/ EECIV/ EFi vehicles. Key thing is you have to know what the EECIV is looking for, and how to continue signal supply. This is easy IF you know what the system is looking for. When you convert to auto, the KOER trigger from the manual gearbox is not engaged, so you cannot read On Board Diagnostic 1.5 (1990 -1995 truck SAE mandated Dealer Trouble Codes) . Ford ensures you can jumeet the EECIV, because the same computer serves many diverse kinds of vehicle. 4 to 12 cylinders, Central Fuel Injection, Bank Fire Port EFi, Sequential Port, MAP Speed Density, MAF Hot Wire, VAM Air meter, Thick Film Ignition, EDIS 6 or 8 semi coil pack, Turboed, SuperCharged, Variable Valve Timing, Broad Band intake manifold tracks, Factory LPG and Gasoline Dual Fuel...the engineers are used to being shot gunned by feature creep from Marketing or Finance or Emissions.
A downward non- compitable change is, say, a triple carb conversion, or an HEi, Duraspark I/II/III ignition.
A turbo or supercharger is an upward change.
All are compatible if you've done your homework and know where to raid the right 60 pin computer pinout schematic. And where to get a sensor to provide the constant data need so the system won't Shut Your Clydesdales down.
I'm on my fifth Toyota RAV4.1 to Ford triple carb six cylinder EECiV conversion. I use the stock Ford computer with Toyota wiring, and a mixture of Essex 90 V6 and Duraspark III sensors. Fords EECIV has many non negotiable's, but it's really easy to make a non standard ignition work with your 1995 if you are aware of what the EECIV is looking for. I help people with MegaSquirt Scoping. A lot of times, people see sense and keep the stock Ford labyrinth of wires and systems, and just trouble shoot them. Unlike others, EECIV or the earlier 1978 to 1983 systems....they don't faze me at all. I grew up surrounded by good automotive engineers who realised that it's easier to deal with systems rather than do a frontal labotomy.
1. The Start Dealer Trouble Code ( OBDI.5 two earths) or ( on Mustangs) the defacto OBDII port for 95 V6s has to be able to work the KOER codes, so anytime you do an auto conversion to a vehicle born stick shift, the whole O2 harness and clutch lock-out goes west, which is why you can't read codes.
2. The Solid State Ignition has to be incrementing and proving response to the EECIV. Spark Out and Spark In and the signals that phase injectors or log ignition pulse have to be sent to the EECIV.
3. The Thick Film Ignition or Base timing SPOUT has to respond to executive commands. Fuel and Spark and Push Start Inductive Control Modules have different base rpm start points, with idle tip in and Barametric MAP cold start ignition timing changes.
4. Ford use either Idle Solenoid Control or what GM call an IAC. Some earlier carbs use five other devices including the humble old choke and vacuum operated throttle modulator, ad well as A/C and Throttle Solenoid Positones, as well the TPS. Base idle settings vary between type, and the Air Control metering devices can be one of four types. Turbo cars have a 3 bar MAP sensor and a MAF sensor. So the whole shooting match is mapped out with satraps and sentinals and a sagelog of settings is compiled against three air, water and EGR and AIR sensors.
5. EGR is automated with all EEC computers, but it can be done manually with the older carb based ssystems. EEECIV "sagelogs" the settings with an electronic DPFE valve sensor.
6. The open and closed loop fuel values from the pulse width modulation signals sent to the injector solenoids complies a vast list of Keep Alive Memory to slew the fuel delivery within in charted limits.
7. The Fuel pump circuit for all EFi Fords varies for 1995s, but HI and Low Perspire pumps are controlled by a relay system which ha's complicated checks and balances for pressure and return flow, with a notoriously difficult fly tongue pickup with a throublesone earing process.
8. For a genreal lookup of parts, I have a 103 item list of Vehicle Emissions Component Identification names, mostly for the 1978 to 1995 cars. The peak of components were the 1985 4 bbl 5.0 Mustangs without Feedback carbs. Your 1995 ha's only about 65 items. By 2003, it was down to 39.