Jrichker, thank you for breaking those codes down! Much appreciated! I've been thinking about the code 96 explanation and there are a few things I remembered that may or may not point to a problem with the fuel pump relay, wiring, grounds, etc.
When we changed out parts in March the car had been garaged for months and only run up to temp about once a week. Upon driving it up and down the street that first time the car sputtered terribly a few times then drove fine, then the low fuel light came on. I thought it was odd as there was between 1/4 and 1/2 tank of gas in the car. I wondered if there may be moisture in the gas tank (I started having issues with the car and garaged it then removed it from full coverage). This is why I didn't fill the tank full if gas prior to garaging it. We added additional gas (not full) and heat. It ran fine as far as no sputtering (which is different to me than misfire).
Fast forward to last week. I started it up to come home (night of the battery issue and day before the starter stuck) and the car stalled right after firing up. I thought that was odd because it has never stalled on me. Fast forward again to tonight. I pulled it out of the garage to wash it (didn't drive it) then when I started it it started right up then stalled. The low fuel light came on for a few seconds then it went out. Started right up again and I pulled it into the garage.
Thoughts? Does this sound like it may be related to the code 96 which may be related to the misfiring with the headlights?
Also, did I get the a-okay for the computer based on the computer codes? Still not sure if I got the 11.
We've started troubleshooting the code related to the fuel pump (96). I have about 3.5-4.0 volts going into the fuel pump relay. With key on there is the same voltage going out. Can somebody tell me how many volts should be going to the fuel pump?
We're taking it from the wires going into and out the relay. It's located under the driver's seat. He put his ground lead to the body and the positive lead going to the wires going into the relay with the key off. That was about 4 volts. He put the positive lead to the wire going out of the relay with the key on and it was the same voltage, the relay was tripping. We thought it should be 12 volts. Could this be the cause of the code? Are we testing correctly? Is there a good resource to trace from it's origin to it's destination?
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
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.
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.
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)
Thank you for all the useful info! We haven't gone any further with the fuel pump troubleshooting. I will be sure to update if and when we find something.
I was looking through the history on this car again and I read the classified ad from 1990 when the previous owner purchased the car. He was the second owner from 1990 until I bought it. Interesting thing I noticed in the ad that I hadn't even thought about when I looked at it originally. It does list the alarm system AND a kill switch. Unless the previous owner removed it, there is a kill
Switch somewhere in the car. I wonder if this may have something to do with my electrical issues? I know normally they hide them. We've been wondering what this button is for, is this a kill switch? I thought though that they hide them or it defeats the purpose of a kill switch?
It's this button near the alarm and just kind of hangs there loose I have t traced it. I just secured it up out of he way when I was nosing around. Does this look like a kill switch? Still, I thought they were hidden. If it is and there is something faulty with it could it cause my problem? If this isn't the kill switch I would assume it's hidden somewhere in the car. I was reading about them last week when I was making sure she didn't get stolen from the curb. Lol.
Just learning about kill switches. It can be part of the alarm (meaning that if I arm the car, set off the alarm and try to start the car it wouldn't start) or it could be a separate switch hidden somewhere in the car? The ad said alarm/kill switch.
More information on anti-theft or "kill" switches.
Note that the Fuel Pump Troubleshooting for 87-90 Mustangs test path, if done correctly, will enable you to determine if there is a "kill" switch causing your problem.
Follow this tech note for the best way to wire a fuel pump kill or anti-theft switch...
Revised 16-Mar-2017 to change wire color and add 91-93 fuel pump wiring diagram.
Note: Use automotive gauge wiring that is rated for 105° C. The wire spool will be marked and the wire may also be marked. The higher temperatures that automotive wiring is exposed to makes this a necessity.
On 86- 91 cars the fuel pump relay is under the driver’s seat, 92 and later cars, the fuel pump relay is under the Mass air duct on the passenger fender well.
Note that the wire colors changed in 1991, so there are two different descriptions.
86-90 model cars:
Cut the red/black wire going to the fuel pump relay. Splice a 16 or 18 gauge wire into the wire and connect it to one side of the switch. Connect the other side of the switch to the other end of the red/black wire going to the fuel pump relay. When you are done the switch should be in the middle of the spliced red/black wire that goes to and comes from the fuel pump relay. Using the control side of the circuit allows you to use light gauge wire and light duty switches. There is less than 1 amp going through the circuit, so you don’t have to worry about voltage drop across the wiring depriving the fuel pump of electrical power.
91-93 model cars:
Cut the Red wire going to the fuel pump relay. Splice a 16 or 18 gauge wire into the wire and connect it to one side of the switch. Connect the other side of the switch to the other end of the Red wire going to the fuel pump relay. When you are done the switch should be in the middle of the spliced Red wire that goes to and comes from the fuel pump relay. Using the control side of the circuit allows you to use light gauge wire and light duty switches. There is less than 1 amp going through the circuit, so you don’t have to worry about voltage drop across the wiring depriving the fuel pump of electrical power.
The design of this plan doesn't require an expensive or heavy duty switch. It just needs to be reliable and able to withstand being turned off and on frequently. When you turn it on, it needs to stay on and not turn off . This type of switch is labeled SPST (single pole, single throw). It is a NOT a momentary contact but a constant contact type switch.
Most push button switches and switches that spring the handle back when you let go of it are momentary contact switches. These will not work for a for a fuel pump kill switch.
The Mustang Gods have smiled down upon us today! Hallelujah!!!!
We did the fuel pump trouble shooting today and everything tested good. We were sitting around and started talking about how the ignition control module went out in my last Mustang and had to be replaced. I lost all power one day when I was driving. No warning, nothing.
We decided just for the hell of it to pull the ignition control module and take it to the auto parts store and have it tested. We went to 5 stores.....this is why. It tested bad at the first store (the guy had an old archaic looking tester that he had to pull a manual out to figure out how to use). We decided to have it tested somewhere else. The second store it tested good. He gave us a paper printout and said that he tested it twice and got it nice and hot. We still weren't convinced. The third store, it tested good once then bad the next few times. Fourth store said they didn't have the capability to test it. The fifth store it tested fine once then bad the remaining times. We decided to buy a new module and he suggested testing the new module before we took it which we did.
Installed the module and took it for a spin around the block. Turned on the headlights, accelerated to shift and hot damn......no misfire.....no popping! Added the fog lights and blower and still no misfire or popping! I don't know if the radio is still losing it's presets. It may or may not be related.