OBD-1 Connector

Around that time Ford was way behind everyone else when it came to viewing live data and retrieving fault codes. I had some of the nicest equipment, but on those, all I could get was fault code numbers, and it took a special sequence of procedures and five to ten minutes to do what you could do on a Chrysler product in less than 15 seconds.

You're better off fashioning an indicator light that you can connect to the test socket. How to do that is shown in the service manual. If you can't find that, I'll see if I can dig up an old manual at home for the instructions. Ford came out with a rather archaic tool, but it was obsolete after just one year so you won't find them at any dealerships.

Look at the production date on the door sticker. If it's late in the year, you may have an early production '87 model. There is no reference to a diagnostic connector or fuel injection for '86 models that I can find on the online service manuals. For the '87 wiring diagrams, they don't show the connector. They only show wires with designations that they "go to the diagnostic connector". You're just supposed to know which one is which by their colors, I guess. I found a white. Red wire that goes to the Engine Computer. There's going to be a ground wire and a 12 volt power supply wire in that connector too. I DO remember that the single pigtail wire goes to the fuel pump.

I can find a four-wire test connector for the 4.9L and the 5.8L, but not the 5.0L. The wires are shown individually for the 5.0L. There's a white / red wire that connects to pin 48 of the Engine Computer.

OOPS! I just found a three-wire connector for the 5.0L. There's a tan / light green wire that goes to pin 22 of the Engine Computer and to one end of the coil in the fuel pump relay. It appears the computer grounds that wire to turn the fuel pump on.

Another wire is tan / red. That goes to pin 17 of the computer. It looks like that's where the digital signal comes from. The 5.8L uses that wire too.

Those are both at the ends of the connector. In the middle is a black / white wire that goes to pin 46 of the computer. That appears to be a 5.0 volt supply because it goes to over a half dozen other sensors that typically run on 5.0 volts.

That white / red wire is shown separately and is listed for "5.0L STI". That may be not used on your truck.

Almost everything electrical goes to ground which is the negative battery terminal. They just run it to the body, frame rail, engine block, or battery, depending on which is most convenient. All wiring diagrams are simplified by just showing a ground symbol so there's no way to say any items are connected / related in the circuit.

Since this is a sensor or solenoid that runs on vacuum or switches a vacuum source on and off, it should be shown on the sticker under the hood.

Given the three wires I found for the test connector, there's no ground wire in it and no 12 volt supply so your scanner has to be either self-powered with an internal battery or it will need to use a pair of wires that clip right to the battery cables. I have an older Monitor 4000 that works that way. For my newer cars I have a Chrysler DRB3. That gets its power through the test connector but Chrysler had a ground and 12 volt wire in their connectors since '83.

Injectors rarely stick. Excessive fuel is almost always caused by the Engine Computer commanding too much fuel in response to an incorrect sensor reading. There is a range of signal voltages sensors produce, or in the case of Fords, which always have to be different than everyone else, a range of square wave frequencies they produce. If the voltages go outside the acceptable range, that's what sets a diagnostic fault code. It is still possible for a sensor to develop the wrong voltage, but one that's still within the acceptable range. On Chrysler products the sensor that has the biggest say in fuel metering calculations is the MAP sensor. All other manufacturers use a mass air flow sensor except for a few models here and there, then that one is the main one for fuel metering.

A cracked or leaking vacuum hose going to a fuel pressure regulator will cause fuel pressure to be too high, and that will dump too much gas into the engine. A leaking regulator can do that too. GM has a lot of trouble with that on some of their engines.

I'm not sure what you mean by "all sensors have been replaced". If you just replaced many of them as a guess, the Engine Computer is going to be confused until it learns the characteristics of each one. Since it compares signal voltages to other sensors and engine operating conditions, you can expect less than ideal performance for a while. If you're going to replace multiple sensors, replace one at a time, then give the computer a chance to learn its parameters for a day or two before introducing another variable.

When you replace a sensor in response to a diagnostic fault code, that sensor is actually the cause of that code about half of the time. First you have to eliminate wiring and connector problems, and mechanical issues related to that sensor.

Most fuel pressure regulators vary fuel pressure in response to changes in intake manifold vacuum, so they have a vacuum hose attached to them. Pop that hose off and check for wetness inside it. If there's fuel in the hose, the regulator is leaking and that extra fuel goes into the engine where it causes an excessively-rich condition.