I have a 93 gt 5.0. i think the fuel pump is out,but i can hear the pump come on when i turn the key on but doesn't start thou.what else do i check ?????
fuel pump out????
- Thread starter nmcobradude
- Start date
foxbodymike87
Active Member
- Jul 12, 2011
- 739
- 35
- 39
will i have spark flash at the plug boots by the spark plugs. that i have a cure for but didnt get a chance to fix it cuz the car just went out.
i was thinking the relay might have went out or the fuel filter is clogged???
i was thinking the relay might have went out or the fuel filter is clogged???
Factory fuel pumps are notorious for going out, I worked on a 90 GT a while ago and the fuel pump would start on key on, but under load the engine would loose power. Was confused for a while, but one day came out and would not start and you could hear the fuel pump not running. The little motor that runs the pump can get a bad spot in it and effect fuel pressure, and if it stops in the perfect wrong spot, it won't run at all. Do you know if you are still running on the stock fuel pump?
yea i lose power under load 3 times. the first two times it just went out and i started it back up and it ran just find.so i drove it to work and went out again .so the last time it went out it would try to start so i pulled it home. yea its stock fuel pump .
I would deffently say you need a new fuel pump, and while your at it make sure you do the in line fuel filter also. A stopped up fuel filter puts more load on the fuel pump and can lead to a very short life for your new fuel pump. Good luck!
Fuel Pump Troubleshooting for 91-93 Mustangs
Revised 21-Oct-2011 to Add location of fuel pump relay on 91 model year cars
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 upper RH corner to
ground.
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 upper LH 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 Relay:
On 91 cars, it is located under the driver's seat.
On 92 and 93 cars it is located under the MAF. Be careful not to confuse it with the A/C WOT cutoff relay which is in the same area. 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.
Theory of operation:
Read this section through several times. If you understand the theory of operation,
this will be much easier to troubleshoot. Refer to the diagram below frequently.
Diagram of the fuel pump wiring for 91-93 cars.
The electrical circuit for the fuel pump has two paths, a control path and a power
path.
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.
The control path consists of 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 relay coil and then from the relay coil to the
computer (light blue\orange 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 (pink/black wire) goes to the fuel pump relay
contacts. When the contacts close because the relay energizes, the power flows
through the pink/black wire to the contacts and through the dark green\yellow
wire to the inertia switch. The other side of the inertia switch with the
brown\pink wire joins the pink/black wire that connects to the fuel pump. The fuel
pump has a black wire that supplies the ground to complete the circuit.
Power path:
Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay).
No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92
or later models the fuel pump relay is located under the Mass Air meter. Watch out for the
WOT A/C control relay on these cars, as it is located in the same place and can easily be
mistaken for the fuel pump relay.
Relay: Turn on the key and jumper the ECC test connector as previously described. Look
for 12 volts at the dark green\yellow 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.
Inertia switch:
The location for the inertia switch is under the plastic for the driver's side taillight.
There should be a round plastic pop out cover over it, remove it to access the switch button.
With the test connection jumpered and ignition switch in The Run position as described above, check
the brown/pink 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 dark
green\yellow (inertia switch input) and brown/pink wire (inertia switch output). Power on the
dark green\yellow wire and not on the brown/pink wire means the inertia switch is open.
Press on the red plunger to reset it to the closed position. Sometimes the inertia switch will
be intermittent or will not pass full power. Be sure that there is 12 volts on both sides of the
switch with the pump running and that the voltage drop measured across the switch is less
than .75 volts.
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.
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.
Control path:
Relay: The red wire for the fuel pump relay coil gets its power feed from the ECC relay.
No 12 volts here, and the ECC relay has failed or there is bad wiring or bad connections
coming from it. The ECC relay is located on top of the computer, which is under the passenger’s
side kick panel. It is not easy to get to, you must have small hands or pull the passenger side
dash speaker out to access it.
Relay: The light blue/orange wire provides a ground path for the relay power. With the test
connector jumpered according to the previous instructions, there should be less than .75 volts.
Use a test lamp with one side connected to battery power and the other side to the light blue/orange
wire on the fuel pump relay. 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. Remove the test jumper from the ECC test connector.
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.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
for help on 88-95 wiring Mustang FAQ - Engine Information
Fuel pump runs continuously:
The fuel pump relay contacts are stuck together or the light blue/orange 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 light blue/orange 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
Revised 21-Oct-2011 to Add location of fuel pump relay on 91 model year cars
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 upper RH corner to
ground.
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 upper LH 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 Relay:
On 91 cars, it is located under the driver's seat.
On 92 and 93 cars it is located under the MAF. Be careful not to confuse it with the A/C WOT cutoff relay which is in the same area. 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.
Theory of operation:
Read this section through several times. If you understand the theory of operation,
this will be much easier to troubleshoot. Refer to the diagram below frequently.
Diagram of the fuel pump wiring for 91-93 cars.
The electrical circuit for the fuel pump has two paths, a control path and a power
path.
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.
The control path consists of 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 relay coil and then from the relay coil to the
computer (light blue\orange 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 (pink/black wire) goes to the fuel pump relay
contacts. When the contacts close because the relay energizes, the power flows
through the pink/black wire to the contacts and through the dark green\yellow
wire to the inertia switch. The other side of the inertia switch with the
brown\pink wire joins the pink/black wire that connects to the fuel pump. The fuel
pump has a black wire that supplies the ground to complete the circuit.
Power path:
Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay).
No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92
or later models the fuel pump relay is located under the Mass Air meter. Watch out for the
WOT A/C control relay on these cars, as it is located in the same place and can easily be
mistaken for the fuel pump relay.
Relay: Turn on the key and jumper the ECC test connector as previously described. Look
for 12 volts at the dark green\yellow 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.
Inertia switch:
The location for the inertia switch is under the plastic for the driver's side taillight.
There should be a round plastic pop out cover over it, remove it to access the switch button.
With the test connection jumpered and ignition switch in The Run position as described above, check
the brown/pink 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 dark
green\yellow (inertia switch input) and brown/pink wire (inertia switch output). Power on the
dark green\yellow wire and not on the brown/pink wire means the inertia switch is open.
Press on the red plunger to reset it to the closed position. Sometimes the inertia switch will
be intermittent or will not pass full power. Be sure that there is 12 volts on both sides of the
switch with the pump running and that the voltage drop measured across the switch is less
than .75 volts.
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.
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.
Control path:
Relay: The red wire for the fuel pump relay coil gets its power feed from the ECC relay.
No 12 volts here, and the ECC relay has failed or there is bad wiring or bad connections
coming from it. The ECC relay is located on top of the computer, which is under the passenger’s
side kick panel. It is not easy to get to, you must have small hands or pull the passenger side
dash speaker out to access it.
Relay: The light blue/orange wire provides a ground path for the relay power. With the test
connector jumpered according to the previous instructions, there should be less than .75 volts.
Use a test lamp with one side connected to battery power and the other side to the light blue/orange
wire on the fuel pump relay. 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. Remove the test jumper from the ECC test connector.
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.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
for help on 88-95 wiring Mustang FAQ - Engine Information
Fuel pump runs continuously:
The fuel pump relay contacts are stuck together or the light blue/orange 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 light blue/orange 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
Attachments
thanks for the info! it well help out. Also the fuse link whats the color of the wire? and when it is blowned does it have a color??
ID89GT
10 Year Member
Hook up a fuel pressure gauge and see what it is sitting at.. If its low then you know your pump is not up to par. Replace the pump, and the filter at the same time, good to go.
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.
Choose the fuse according to the wire size.
Wire size current table:
http://www.stangnet.com/mustang-for...-wire-gauge-current-capacity-lenght-chart.gif
18 gauge wire = 5-8 amps
16 gauge wire = 10-12 amps
14 gauge wire = 15-17 amps
12 gauge wire = 20-25 amps
10 gauge wire = 30-40 amps
8 gauge wire = 50-60 amps.
Keep in mind that the wire size in the chart is for the circuit itself, not the size of the fuse link. The packages of fuse link repair material you can get at the auto parts stores also will have a current rating on them.
See http://fordfuelinjection.com/?p=7 for some excellent tips of soldering wires for best electrical performance.
Attachments
Hey guys,
I'm new here but I've got what I think is the same problem. I've got a '93 LX 5.0 with a stock fuel pump. A while back it started to lose power with the pedal anything more than half way down. At half throttle or less, it would be fine. I've still to apply some of the things you guys talk about here, but I have changed the filter near the tank, and all the plugs. It's supposed to be in the shop in the next few days and I'll let you know what happens. A couple of questions though. Is this the problem? Can I replace this pump myself (not a pro, but not too bad either)? If it does need to be replaced, are there any good upgrades I should consider, ie racing fuel pump or one I should use if I'm gonna throw a supercharger on it later? Finally, what's the best place to buy it from? Any help would be appreciated. Thanks.
I'm new here but I've got what I think is the same problem. I've got a '93 LX 5.0 with a stock fuel pump. A while back it started to lose power with the pedal anything more than half way down. At half throttle or less, it would be fine. I've still to apply some of the things you guys talk about here, but I have changed the filter near the tank, and all the plugs. It's supposed to be in the shop in the next few days and I'll let you know what happens. A couple of questions though. Is this the problem? Can I replace this pump myself (not a pro, but not too bad either)? If it does need to be replaced, are there any good upgrades I should consider, ie racing fuel pump or one I should use if I'm gonna throw a supercharger on it later? Finally, what's the best place to buy it from? Any help would be appreciated. Thanks.
foxbodymike87
Active Member
- Jul 12, 2011
- 739
- 35
- 39
you can do the pump yourself..just make sure the tank it empty so its easier to get out and when you take the pump out replace with a bigger pump so incase you wanna get more power you dont have to take it out again..summit,jegs, mustang catalog
How do you know it is the fuel pump and not something else? Throw parts and money until you finally fix it and you''ll be poorer and tired.
Do some diagnostic thinking:
Is the lower power worse as the engine warms up?
Have you dumped the codes? Codes can be present without the Check Engine Light being on.
Have you done a cylinder balance test?
Have you done a compression test?
Once you have done all the above, if you need more help, start your own thread. It is bad manners to steal someone else's' thread, its like stealing food off their plate.
Thanks for the replies. No I'm definitely not just gonna throw money at it, just looking for advice. I dropped it off this morning and the guys gonna read the compression, check the volts, read the codes...that old game. My car sat for three years with the fuel preservative in it, and when I got it back there was a bunch of stuff wrong with it. Had a bad battery as well, so I think most of the codes have been dumped, but we'll see. Any recommendations on size of the new fuel pump, maybe a psi range I should look for?
As far as stealing someone else's thread...really? I know I'm new here, but is that this forums policy? The other forums I've been on usually complain when you start a new thread about something when there's already one out there. Oh well, I'll abide if that's the case...
As far as stealing someone else's thread...really? I know I'm new here, but is that this forums policy? The other forums I've been on usually complain when you start a new thread about something when there's already one out there. Oh well, I'll abide if that's the case...
Try the filter first, with the quality of fuel today the filter could be clogged. A couple weeks ago my pump started sounding funny when it primed, and it was slowly dropping fuel pressure when cruising. I had a fuel filter sitting on the shelf so i swapped that in and the priming sound went back to normal, and the fuel pressure was where it should have been.
This all happened the day before i was going to a local dyno day, the car made 384 hp the first pull, i pulled a total of 8 degrees of timing out of it cause it was detonating and power ended at 395. About a week ago i talked to my cam guy and he told me something was way off, that i had a bad tank of fuel, so i rented a local dyno, and filled the tank with Sunoco 93 octane fuel. The car made 428hp on a good batch of pump fuel, i was suprised to say the least. Be careful where you buy your fuel from
Similar threads
