Ok jrichker this is for you. I need to know the wire schematics from auto zone ( I looked and couldn't figure out how to search for them ), for trouble shooting cause my fuel pump isn't getting power to it for some reason. I jumped the + on the battery to the + on the fuel pump and they came on, but the pumps themself aren't getting power and nothing with the key. The inertia switch is ok, I also know the relays are ok too as well as the fueses.
JRICHKER I NEED YOUR HELP!
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Fuel Pump Troubleshooting for 86-90 Mustangs
Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 2-5 seconds and shut off. This on and off again cycle helps to prevent
flooding the engine when cranking. To trick the fuel pump into running, find the ECC
test connector and jump the connector in the upper RH corner to ground.
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 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.
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). 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.
Diagram courtesy of AutoZone
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, 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.
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.
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 will have to drop the tank to inspect the pump power and ground connector
and the pump wiring chassis ground.
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. You should see less than 1 Ohm between the black wire(s)
and ground. The chassis ground is up near the spare tire shell. 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. 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
Fuel Pump Troubleshooting for 86-90 Mustangs
Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 2-5 seconds and shut off. This on and off again cycle helps to prevent
flooding the engine when cranking. To trick the fuel pump into running, find the ECC
test connector and jump the connector in the upper RH corner to ground.
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 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.
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). 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.
Diagram courtesy of AutoZone
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, 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.
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.
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 will have to drop the tank to inspect the pump power and ground connector
and the pump wiring chassis ground.
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. You should see less than 1 Ohm between the black wire(s)
and ground. The chassis ground is up near the spare tire shell. 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. 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
Thanks JRICHKER! My buddy and I tried to trick the fuel pump as stated above but it did not work. So we will read on and see what happens. We worked on this for about 3 hours. No luck. I'm going to replace the fuel pump relay just in case anyway.
Ben
Ben
ok so we tried everything in the trouble shooting. Nothing! We put a new relay in no good. BUT i dont understand is they say the top right wire/connecter on the dianostic port. Whats top right? photo1 in posted or photo 2? We did all the OHM test of every wire we probed the ECU nothing!!!!!!!!!!!!!!! BUT if we dont hook into the correct terminal on the test port will all the tests be in correct? Do we need to key on off for every step of the test since the pumps only cycle for a few seconds when you key on to prime the system,or will the pumps run continously doing the jumper wire in the ECU test port? here are the pics
1 yes or no?
2 yes or no?
If anyone else can help please feel free to chime in!!
1 yes or no?
2 yes or no?
If anyone else can help please feel free to chime in!!
Flip the test connector over and look for a tan wire with a green stripe. That is the fuel pump relay test ground.
The diagram below shows the test connector wiring pinout. The clue to the wiring positions is the flat on one side of the test connector.
The diagram below shows the test connector wiring pinout. The clue to the wiring positions is the flat on one side of the test connector.
DNA DOA, can't really add anything to this that JRichker hasn't provided!! But, I am going through this same issue on a 4Cyl conversion car for a friend. It is a nightmare. 89 car with hacked wiring!!! Started out no spark/no fuel pump. The main EEC relay was full of water/rust in the passenger kick panel??? Now has spark but no fuel still!! I will keep you posted if I find anything that may help you. I only had about an hour or so today to go look at it.
Good Luck!!
Good Luck!!
Thanks for the info guys. We spent another 5 hours on it today. We tried everything we could think of but got burned out. I think something in my head is starting to bleed. All the fuses are in, inertia switch is fine, I know the pumps work but we can't get the pumps to kick on using the Dia. Conn. trick. We checked resistance in both directions from the Dia. Conn to both the ECU and fuel pump relay and everything came up 0.00. So no broken wires and there seems to be no power from the fuel pump relay back to the interia switch (checked for resistance here too. ) then of course to the pumps. So we will hit it again tomorrow before I set fire to the thing. And yes wiring is fun! Whatever.
If we find anything out Nstylx I will post the results. Thanks again.
Ben
If we find anything out Nstylx I will post the results. Thanks again.
Ben
jrichker that is what we did i flipped it over and nothing! there is no way that the computer could of took a **** (like the artical in the 1st post claimed) cause we took the car apart running fine (other then a slight nitrious explosion 
) my question is what about running the pumps off a switch so that they are controlled that way,would that effect the way the car will run or be able to be tuned?DNA DOA before you set it a fire tomorrow i need a few parts for mine 
say turbo big and littles oh yeah and new wheels studs 
see ya at 9 so we can 
! whats for lunch 
peace
john
) my question is what about running the pumps off a switch so that they are controlled that way,would that effect the way the car will run or be able to be tuned?DNA DOA before you set it a fire tomorrow i need a few parts for mine say turbo big and littles oh yeah and new wheels studs see ya at 9 so we can peacejohn
Go back and re-read my post Fuel Pump Troubleshooting for 86-90 Mustangs. Check out the diagram for the circuit.
There are 8 components and 8 wires that connect the components together. There is not a lot of stuff to check,
although some of it may be difficult to get to. Don't let the idea that it is electrical and computerized throw you off track.
The tan/lt green wire is on the test connector, the fuel pump relay and the computer.
Jumpering the tan/lt green wire on any one of those to ground should make the pump run if the pump, relay, and power are good.
If it does not, then you start going through the process of finding what does not have power or ground.
There are 8 components and 8 wires that connect the components together. There is not a lot of stuff to check,
although some of it may be difficult to get to. Don't let the idea that it is electrical and computerized throw you off track.
The tan/lt green wire is on the test connector, the fuel pump relay and the computer.
Jumpering the tan/lt green wire on any one of those to ground should make the pump run if the pump, relay, and power are good.
If it does not, then you start going through the process of finding what does not have power or ground.
Attachments
We spent another 4 hours today, and we did perform all of the tests above and we even swaped out my buddy's 9AL with my 9AL and his fuel pump kicked on. So we have narrowed it down to the PC is good. We think it could be a bad ground off of the PC.
How do we find this "dedicated power ground" wire???? We think we may have cut it when we were hinding some of the wires from the lume. We can't find it where it should be next to or near the starter solenoid. "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."
Thanks,
Ben
How do we find this "dedicated power ground" wire???? We think we may have cut it when we were hinding some of the wires from the lume. We can't find it where it should be next to or near the starter solenoid. "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."
Thanks,
Ben
did you pull my **** off before you set it on fire!
The description you posted is about as good as I can do.
The black wire with a green stripe comes out of the body wiring harness near the starter solenoid.
It will have a round cylinder that looks a lot like an inline fuse holder. One end of the cylinder connects to the body wiring harness and the other is part of the negative battery ground cable.
Here's a drawing showing what the original battery ground/computer ground looks like...
Oh Dear God! That looks familiar.
Hey John, remember when I said, "What is this stupid thing welded to the inside frame for?" Then we cut it off. You know, the thing that looked like a neg. ground cable. OH-K... Getting closer.
I TOLD YOU TO NEVER LET ME HOLD A PAIR OF SIDE CUTTERS! But you wouldn't listen. Notice I didn't call the side cutters the other name. PC. Just trying to do my part.
Thanks again jrichker, you are my new God, all sacrifices from now on, will be in your honor. I think we can take it from here. Will post results soon.
Hey John, remember when I said, "What is this stupid thing welded to the inside frame for?" Then we cut it off. You know, the thing that looked like a neg. ground cable. OH-K... Getting closer.
I TOLD YOU TO NEVER LET ME HOLD A PAIR OF SIDE CUTTERS! But you wouldn't listen. Notice I didn't call the side cutters the other name. PC. Just trying to do my part.
Thanks again jrichker, you are my new God, all sacrifices from now on, will be in your honor. I think we can take it from here. Will post results soon.
What the hell are side cutters??????? ohhhhhhh you mean let you work the dikes ! Yeah your right your fired!!!!!Well as far as i'm concerned you shoulda use that POS dyno sheet to start the fire! jrichker so we should be able to find that wire in the harness and ground it to the frame/body somewhere and call it good or the battery also? Or can we just run it to the trunk to the - on the battery? OR could we just splice the wire from the ECM and run it to the battery and go that route if we caint locate the wire in the harness. Do you know why it is a inline fuse type of deal,is it just to quick disconnect it to change battery cables? Also if we run it to the trunk where the battery is now located and ground it on the battery like stock do we still need the wire comming off it with the eye connecter and ground that also to the car?Is this wire in the driver side loom of wires or does it come from the passenger side loom of wires over to the drivers side? As ben said you've been alot of help! peace
john
! Yeah your right your fired!!!!!Well as far as i'm concerned you shoulda use that POS dyno sheet to start the fire! jrichker so we should be able to find that wire in the harness and ground it to the frame/body somewhere and call it good or the battery also? Or can we just run it to the trunk to the - on the battery? OR could we just splice the wire from the ECM and run it to the battery and go that route if we caint locate the wire in the harness. Do you know why it is a inline fuse type of deal,is it just to quick disconnect it to change battery cables? Also if we run it to the trunk where the battery is now located and ground it on the battery like stock do we still need the wire comming off it with the eye connecter and ground that also to the car?Is this wire in the driver side loom of wires or does it come from the passenger side loom of wires over to the drivers side? As ben said you've been alot of help! peacejohn
No god here, just an ordinary guy trying to help out his fellow Mustang fans.
Peel back the tape on the harness where it ends under the ignition coil. Crimp or solder a new terminal on the black/green wire. Then find a nice clean spot and sand off the paint so it is all nice and shiny. Ground the terminal you just crimped on the black/green wire there. Put some dielectric grease over the connection to prevent corrosion and you are done. It works best if you ground the 10 gauge pigtail wire from the battery negative cable in the same place.
After this, you will have a new view on the importance of grounds in automotive wiring...
Hope that fixes you problems.
Joe R.
Black Sun 5.0
Founding Member
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