Here's a book that will get you started with how the Ford electronic engine control or "computer" works.
Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst: ISBN 0-8376-0301-3. See the link below for vendor, price and availability
https://www.google.com/search?q=ford+fuel+injection+&+electronic+engine+control+pdf&sxsrf=ALeKk005Ob4abX8nWnbpgW4b1hHIOwGMzQ:1624893444667&ei=BOjZYNCEKNKj5NoP1s-U6Ao&oq=Ford+Fuel+Injection+&+Electronic+Engine+Control+&gs_lcp=Cgdnd3Mtd2l6EAEYADICCAAyBggAEBYQHkoECEEYAFCS-3NYkvtzYI2ZdGgAcAJ4AIAB5AGIAawCkgEFMS4wLjGYAQCgAQKgAQGqAQdnd3Mtd2l6wAEB&sclient=gws-wiz&safe=active&ssui=on
Select books and then select search. Use the ISBN number (without dashes or spaces) to do a search Use the ISBN number and your local library can get you a loaner copy for free. Only thing is you are limited to keeping the book for two weeks. It is very good, and I found it to be very helpful.
Computer system differences in 86-95 Mustangs.
Revised 15-Jan-2018 to add requirements for larger fuel system components to support large changes in airflow through the engine.
All 5.0 foxbody engines from 86-95 are OBDI
OBD1 comes in Speed Density and Mass Air Flow versions. It differs from OBDII in that diagnostic data cannot be streamed through the diagnostic port in a real time mode. The diagnostic data is stored in volatile memory and dumped on command by an external jumper or code reader connected to the computer’s diagnostic port. Watching the Check Engine Light, an external test light or voltmeter are all that is need to dump the codes on an OBDI system. An OBDI code reader can be used, but it isn’t an absolute necessity.
ODBII is capable of streaming data through the diagnostic port in real time mode. It requires a code reader that handles the OBDII data format. No code reader, no way of knowing what the codes are. The plus is you can watch changes in sensor data as they happen, and use the information to plan changes in the computer's program. OBDI requires a laptop & some specialized hardware to do the same thing.
Both OBDI & OBDII have adaptive learning to accommodate changes in sensor output, so as the sensors and airflow values change, the computer adjusts for them. Mass Air systems have a greater range of adaptive learning than Speed Density.
Speed Density uses Manifold vacuum (MAP), Throttle position (TPS) and RPM, & Air Temperature (ACT) to guess how much air the engine is pulling in. Then it uses all of them plus the O2 and ECT sensors to calculate the air/fuel mixture. It is dependent on steady manifold vacuum and minimal changes in airflow from the stock engine configuration to maintain the proper air/fuel ratio. Change the airflow or vacuum too much and the computer can't compensate for the changes, and does not run well. Forget about putting a supercharger, turbocharger or monster stroker crank in a Speed Density engine, because the stock computer tune won’t handle it. Every time you seriously change the airflow through the engine, you need a new custom burned chip to make the engine run at peak performance. Most aftermarket cams will not work well with Speed Density, and that includes the Ford letter cams.
Mass Air uses a Mass Air Flow meter (MAF) to actually measure how much air is being pulled into the engine. The computer uses this information and inputs from the O2, TPS, ACT, ECT, RPM and Barometric Pressure (Baro) sensors to calculate the proper air/fuel ratio. It is very tolerant of changes in airflow and vacuum and tolerates wild cams, high flowing heads, and changes in displacement with minimal difficulties. Just remember that large changes in airflow require more fuel than the stock fuel system can deliver. At that point, you will need larger injectors and a larger fuel pump to make the engine run like it is supposed to. Larger injectors can be used with either an aftermarket calibrated MAF or a custom dyno tune. This makes it possible to use the stock computer with engine displacements from 302-408 cu in, and make many modifications without a custom dyno tune chip. Put a new intake manifold on your 331 stroker and the computer figures out how much more fuel to deliver without having to have a new chip burned to accommodate the extra airflow.
The EFI will tell you what's wrong most of the time with just a simple dump of the codes.
EFI RULES on the street for a car that is driven in all kinds of weather, up and down mountains and gets great gas mileage. EFI will make just as much power as a carb and be easier to drive on the street. If isn't hard to tune if you know what you are doing.
There isn't a carb made without computer assist that can do all those things as well as EFI can. The only possible exception would be the IDA or DCOE Webers which cost major $$$ - like $3000 for 4 each IDA 48's and a manifold.
Surging idle - here's the fix... You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the
[URL=" http://forums.stangnet.com/showthread.php?t=698148"]Surging Idle Checklist[/URL]. Over 50 different people contributed information to it. The
first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money.
It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.
It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.