Rewiring the 87, need some help

98yellowstang

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Feb 15, 2001
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I have an 87 vert, it had a botched up wiring harness in it. So I have gotten the pieces I need from an 89 hatch. I know the vert harness is different, but I will deal with that later. The main issue that needs to be cleared up right now is this:

I have everything wired up that needs wired up (I think) to satisfy the fuel pump relay. When I cycle the key to the "ON" position all of the relay's kick near the dash, but I do not hear the fuel pump cycle. when I move the key to the "START" position, the engine will crank, but with no fuel pump the motor is not going to fire.

The wiring running from the main harness to what I think is the fuel pump, was cut on the donor harness, so I removed it from the botched up harness that I removed. There are 4 wires on it, can anyone tell me if 87 and 89 would have the same colored wires? If not see which ones need connected together.

Just looking for some info. Any and all info is appreciated.

Later
Jason
 
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They "should" be the same color. There are only two wires that connect to the fuel pump; a black for ground, and a pink with a black tracer for power (which is coming from the fuel pump relay). The other two should be for the sender but i do not know what color they are.
 
Well I will verify with dad at home tonight, but I believe 1 yellow, 1 pink, and 2 blacks, all roughly the same gauge and they go down through right beside the spare tire well, and plug into a round 4 prong plug that goes near the gas tank. The color on both the 89 and 87 harness's are the same.

Maybe this would be a better question(s) to help track down this problem:

What criteria needs met in order for the pump to cycle?
What all exactly needs to be hooked up before the pump will cycle?
What voltages should be in each of the 4 wires going down to the plug by the gas tank?
Any differences in the fuel pump circuit between the 87 and 89 cars?

Thanks
Jason
 
Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html for a description of the test connector. If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness. Use a voltmeter to measure the voltage drop across them. There should be less than .75 volt drop across a fuse link.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect for fuel escaping while pump is running.

The electrical circuit for the fuel pump has two paths, a control path and a power path.

The control path consists of the inertia switch, the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the inertia switch (red/black wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (tan/ Lt green wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.

The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source power for any actuator or relay, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Now that you have the theory of how it works, it’s time to go digging.

Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring or connections. There is a mystery connector (one I haven’t found) under the dash somewhere, between the fuel pump relay and the fuse link.

Turn on the key and jumper the fuel pump test connector to ground as previously described. Look for 12 volts at the Light Pink/Black wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed or there is a broken wire in the relay control circuit.
Check the Red/black wire, it should have 12 volts. No 12 volts there, either the inertia switch is open or has no power to it. Check both sides of the inertia switch: there should be power on the Red wire and Red/Black wire. Power on the Red wire and not on the Red/Black wire means the inertia switch is open.

The Tan/Lt Green wire provides a ground path for the relay power. With the test connector jumpered to ground, there should be less than .75 volts. Use a test lamp with one side connected to battery power and the other side to the Tan/Lt Green wire. The test light should glow brightly. No glow and you have a broken wire or bad connection between the test connector and the relay. To test the wiring from the computer, remove the passenger side kick panel and disconnect the computer connector. It has a 10 MM bolt that holds it in place. With the test lamp connected to power, jumper pin 22 to ground and the test lamp should glow. No glow and the wiring between the computer and the fuel pump relay is bad.

If and only if you have followed the test procedure to this point and still haven’t found the problem, the computer is suspect. :(
 
Bringing this back to the top. I am finally getting around to working on this project. If anyone has any more information, it would greatly be appreciated.

jrichker: those links in your post don't work. I was unable to find the test connector so there for unable to do any testing

I appreciate the help.

Later
Jason
 
Update:

The fuel pump relay.... under the seat

Has power at the orange wire, but nothing at the pink or red. I did try to jump over the orange and pink. The pump did run!! So its not the pump. When I tried to start the car though with the pump jumped over and running it did not start.

I have tried 3 seperate used relays and they all act the same as described above.

Thanks for the help.

Later
Jason
 
The EEC Power Relay seems to be the problem.

I have no voltage at the black/org. wire feeding the 12 volts to the relay. There is 12 volts at the solinoid, there is 12 volts after the fuse link G. But there is no power at the end of the wire where the relay connects. So I ran a test wire.... now I have 12 volts on that wire coming into the relay. With the test wire in place I now have 12 volts coming out when the relay is energized, and this is 12 volts on both the red and org/blk wires. But I have no voltage on the red wire back at the inertia switch. I also pulled one of the injector plugs to see if I was getting voltage on that wire (branches off the same leg or the org/blk wire) and there was no voltage at the one injector either.

The fuel pump is not cycling and the injectors are not priming either.

So I guess my only hope now is to chase down the org/blk wire to where it goes into red and hopefully that will lead to something.

Anyone else have any input?

Thanks
Jason
 

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