5.0 Install Fuel Problem

I moved the thread to tech. @jrichker may be able to help you further.

what is this blow off hole you speak of, never heard of it

Same thing happens to me when I eat chili...seriously though, post up some pics. That's not the typical set up. References may help us give you advice.

Fuel Pump Troubleshooting for 87-90 Mustangs

Revised 1-Dec-2015 to add fuse links diagram.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 1-3 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the upper LH corner to ground.





Turn the ignition switch on when you do this test.


If the fuse links 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 Mustangs built before 92. See the diagram to help identify the fuel pump relay wiring colors. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness.
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.

Control 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.


Power Path
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.

Fuse links


Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect. Fuse link material is available at most good auto parts stores. There may even be a fuse link already made up specifically for your car. Just be sure to solder the connection and cover it with heat shrink tubing.

Heat shrink tubing is available at Radio Shack or other electronics supply stores.

See the video below for help on soldering and heat shrinking wiring. There is a lot of useful help and hints if you don’t do automotive electrical work all the time.

View: http://youtu.be/uaYdCRjDr4A


When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). Notice that pin 19 on the computer is the monitor to make sure the pump has power. The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source any power to actuators, relays or injectors, 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.



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

All voltage reading are made with one voltmeter lead connected to the metal car body unless otherwise specified

Check for 12 volts at the red wire on the inertia switch. No 12 volts at the inertia switch, the ignition switch is turned off or faulty or there is no power to the EEC (computer) power relay. To be sure look for good 12 volts on the red wire on any fuel injector.
Good 12 volts means the EEC relay is working. No 12 volts and the ECC wiring is at fault.
Look for 12 volts on the red/green wire on the ignition coil: no 12 volts and the ignition switch is faulty, or the fuse link in the ignition power wire has blown. No 12 volts here and the ECC relay won’t close and provide power to the inertia switch. Check the Red/black wire on the inertia switch, 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. Push the button on the side of it to reset it, and then recheck. Good 12 volts on one side and not on the other means the inertia switch has failed.

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, bad ignition switch or ignition switch wiring or connections. There is a mystery connector somewhere under the driver’s side kick panel, 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.

Pump wiring: Anytime the ignition switch is in the Run position and the test point is jumpered to ground, there should be at least 12 volts present on the black/pink wire. With power off, check the pump ground: you should see less than 1 ohm between the black wire and chassis ground.



The yellow wire is the fuel tank sender to the fuel quantity gage. The two black wires are grounds. One ground is for the fuel tank sender and the other is the fuel pump. The ground for the fuel pump may be larger gauge wire that the fuel tank sender ground wire.

Make sure that the power is off the circuit before making any resistance checks. If the circuit is powered up, your resistance measurements will be inaccurate.

You should see less than 1 Ohm between the black wire(s) and ground. To get some idea of what a good reading is, short the two meter leads together and observe the reading. It should only be slightly higher when you measure the black wire to ground resistance.

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.

Computer: If you got this far and everything else checked out good, the computer is suspect. Remove the test jumper from the ECC test connector located under the hood. Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer and everything else is connected. Turn the ignition switch to the Run position and observe the fuel pressure. The pump should run at full pressure.
If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad.
If it does run at full pressure, the computer may have failed.

Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn the key to the Run position. This can sometimes fool you into thinking the computer has died. Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin. With the ignition switch Off, jumper the computer into self test mode like you are going to dump the codes. Turn the ignition switch to the Run position. The light will flicker when the computer does the self test routine. A flickering light is a good computer. No flickering light is a bad computer.
Remove the test jumper from the ECC test connector located under the hood.

Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the Tan/Lt Green wire has shorted to ground. In extreme ghetto cases, the pump relay may have been bypassed. Remove the fuel pump relay from its socket. Then disconnect the computer and use an ohmmeter to check out the resistance between the Tan/Lt Green wire and ground. You should see more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t jumpered to ground.
If the wiring checks out good, then the computer is the likely culprit.

Prior to replacing the computer, check the computer power ground. The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next to the starter solenoid where the wire goes into the wiring harness

If all of the checks have worked OK to this point, then the computer is bad. The computers are very reliable and not prone to failure unless there has been significant electrical trauma to the car. Things like lightning strikes and putting the battery in backwards or connecting jumper cables backwards are about the only thing that kills the computer.

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

I think part of your problem has to do with the return line being dry. The fuel pressure regulator acts like a restriction....so any pressure over the set amount (45 psi ) should flow through the return line. The pink with a black stripe wire is the power feed to the pump in almost all fords. The on off action is controlled by the computer through the ground side of the fuel pump relay. The computer uses ground to control the relay.

Those tiny holes are there for instances where you would want to use a safety wire to prevent the fitting from coming loose.

poppyredstang said:

Ok so this is what I have to do to get the fuel pump to run. When I connect the red wire on the 8 pin to the pink wire on the body side the pump runs continuously when the key is in the ON position. It does not shut off after 5 seconds.



There is currently nothing connected to the gray connector near the green 8 pin.

When the fuel pump does run, fuel sprays out of the high pressure line near the fuel rail.




There is also nothing connected to this black connector.




So to answer some of your questions:
1. The fuel pump does not run when I jump the test connector (without and without green 8 pin jumped).
2. I have no shrader valve because it is all flex fuel lines so I cant test fuel pressure.
3.When I test the pump relay with the key in the ON position: There is no power at the red wire. There is good power at the pink wire.
4. I dont think it is a computer problem because I swapped computers and the problems didnt go away.
5.The computer ground near the battery is clean and connected.

Completely stumped.....

Click to expand...

Re-read this and step though it -everything you need to find and fix the problem is in it....

All voltage reading are made with one voltmeter lead connected to the metal car body unless otherwise specified.

Key in the Run position and remove the test jumper

Note: The inertia switch is located on the driver's side trunk plastic that covers the tail lights. You may have to remove some screws and plastic to get to it.


Step 1.) Check for 12 volts at the red wire on the inertia switch. No 12 volts at the inertia switch, the ignition switch is turned off or faulty or there is no power to the EEC (computer) power relay. To be sure look for good 12 volts on the red wire on any fuel injector.
Good 12 volts means the EEC relay is working. No 12 volts and the ECC wiring is at fault.

Step 2.) Look for 12 volts on the red/green wire on the ignition coil: no 12 volts and the ignition switch is faulty, or the fuse link in the ignition power wire has blown. No 12 volts here and the ECC relay won’t close and provide power to the inertia switch.

Step 3.) Check the Red/black wire on the inertia switch, 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. Push the button on the side of it to reset it, and then recheck.

Step 4.) After resetting the inertia switch if you have good 12 volts on one side and not on the other, it means the inertia switch has failed. Try pressing on the button on the side of the inertia switch and test it again before replacing it.

poppyredstang said:

Do I try these tests with the jumper on the green 8 pin that I had in my previous picture and the key in the ON position?

Click to expand...

Sorry, I missed that.
Key in the Run position and remove the test jumper

Think about what you observed:
1.) There is power on the red wires for the fuel injectors; that means that the ECC power relay is working supplying power to the computer and inertia switch wiring.

2.) You have no power to the inertia switch. That means some wiring harness isn't plugged into it's' mating half. The connector that isn't connected to anything may be part of the answer. Clean the wiring with solvent and post the wire color with stripe. The wire colors aren't there to make it look impressive or pretty. Ford has wiring spec that spells out what circuit the wire colors connect to. If one of the wires is red, you have found one half of the inertia switch wiring. Look for the other half that mates the connector and you are on your way towards getting this problem fixed.

Since you have a 90 Mustang, the two odd connectors are probably for the airbag sensor feed to the airbag computer.

poppyredstang said:

I could run a new wire to the inertia switch but I'm not exactly sure when to run it from so it signals the pump properly.

Click to expand...

Read the diagram I posted OR do an exhaustive hunt for the to red wires and where they mate together.

poppyredstang said:

jrichker thanks for bearing with me on this. Latest update: I ran a wire from the orange/black wire at the EEC relay to the red/black wire at the fuel pump relay. Turned the key to RUN and the fuel pump did not run. Changed the fuel pump relay out with a spare and still no fuel pump running. Then I took a test light, attached the ground end to the body of the car and pushed the point in to the tan/green wire on the fuel pump relay. As soon as the test probe hit the port, the fuel pump started running. I took the test light out and I put a jumper wire from the diagnostics connector to ground and the fuel pump did not run.

By the way, when the pump does run it is still spraying fuel out of the high pressure line.

Click to expand...

Can you read and understand the fuel pump diagram I posted?

The fuel pump test path makes the assumption that you can read circuit diagrams and understand how simple electrical components work in a circuit. Without that knowledge, your troubleshooting success is going to have a very low percentage success rate.