OBD-1 Connector

Tiny
SALEENS331
  • MEMBER
  • 1986 FORD F-150
  • 5.0L
  • V8
  • RWD
  • AUTOMATIC
  • 190,000 MILES
On my '86, it had optional fuel injection. On this EFI 5.0L engine, I am able to hook up an OBD-1 scan tool under the hood. My scanner won't connect to the computer, but it did on another car I tried. I have found wiring diagrams, but none include the wires for the scanner connector. Where can I find a diagram for the scanner wires, or where do the wires go exactly?
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Tuesday, December 29th, 2015 AT 6:32 PM

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Tiny
CARADIODOC
  • EXPERT
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.
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Tuesday, December 29th, 2015 AT 7:31 PM
Tiny
SALEENS331
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I looked at the sticker and this truck was produced in November of 1985. I know it is an '86 because body style was different in '87. I also know this came with this engine and fuel injection because I found the build sheet for the truck inside. I am confused, though, because I cannot find any other EFI '86 trucks. There are only three wires in the connector, and I know one is for the fuel pump. I found in my scanner manual that the other two are a self test out and signal return. Also, that separate wire is self test in. My problem is that all of the wires are shrink wrapped, and there are many wires with the same color as the connector wires. I want to just track them to the ECM connector and splice in new wires, but I cannot tell which ones they are.
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Thursday, December 31st, 2015 AT 9:38 AM
Tiny
CARADIODOC
  • EXPERT
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.
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Saturday, January 2nd, 2016 AT 2:20 PM
Tiny
SALEENS331
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Okay, thank you very much. I do not see why wires would be cut under the factory shrink wrap, so I have been checking in exposed areas. It appears that the wires are good, but I noticed one of the wires in the OBD-1 Connector splits and has one end go to the negative battery post, and the other goes to a plug that hooks up to a vacuum switch that is bolted on the inside of the passenger fender, behind the battery. Do you know what this switch is? I might be able to replace it and the scanner work. Thank you so much for your time!
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Sunday, January 3rd, 2016 AT 3:47 PM
Tiny
CARADIODOC
  • EXPERT
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.
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Monday, January 4th, 2016 AT 6:24 PM
Tiny
SALEENS331
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My scanner has an internal battery. I am still not sure about wire connections. I ordered that sensor I asked about, it was the MAP. I also got an ECT because this truck needs starting fluid when below about 40 degrees, but not at anything higher (and this is on the first start of the day only, even if the next one is 12 hrs. Apart.) I am also going to go ahead and get a new ACT, because it shudders when cold and bogs down under acceleration. Who knows, the scanner might connect once these are put in, if somehow a short in one would effect the scanner. Either way, I believe these three sensors might help my case a bit. Then, I will get wires, plugs, cap and rotor, etc. Thanks!
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Friday, January 8th, 2016 AT 7:12 PM
Tiny
SALEENS331
  • MEMBER
Also, seeing that the exhaust sprays gas like crazy, I assume I have injectors stuck open. If I find this to be true, is replacing them the best option?
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Sunday, January 10th, 2016 AT 6:06 AM
Tiny
CARADIODOC
  • EXPERT
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.
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Monday, January 11th, 2016 AT 5:08 PM
Tiny
SALEENS331
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So should I concentrate on fuel regulator vacuum, seeing all sensors have been replaced.
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Tuesday, January 12th, 2016 AT 5:55 AM
Tiny
CARADIODOC
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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.
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Wednesday, January 13th, 2016 AT 4:02 PM
Tiny
SALEENS331
  • MEMBER
Okay, will check. Thanks! One other thing, my fuel gauge does not work. It randomly quit working. I know a yellow/white wire goes to the gauge, but I found a common plug for the whole gauge cluster. Do you think I should check the wire first, or try to test the gauge. I think it is fine. It moves a slight amount from tank to tank, but not very much. Also, I know the float in the tank is not hung.
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Wednesday, January 13th, 2016 AT 5:38 PM

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