Electrical Eec-iv Wiring Issues

85mcLaren

Member
Feb 26, 2004
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Have a little problem on a 90 GT. Went to start it a few days ago after using it two weeks prior with no problems and I noticed the fuel pump would not kick on.

Following some of jrichker's diagrams, I jumped (grounded) the fuel pump from the test connector under the hood and she turned on fine.

Then I went to plug in my scan tool - and noticed it would not pick up ANY codes or display a '11'. In other words - it was dead. No actuators or anything was turning on when I hit the test button.

So I started a minor diagnosing procedure. I replaced my EEC relay for the heck of it and then checked pin1 on the harness (with key off and key on) and do have approx 11.50 volts.

I then turned key on and check pins 37 and 57 as I believe these are the pins that should receive 12 volts after the key is on. I have 11.50 volts from 57, BUT weird figures from pin 37 (meter was all over the place in the hundreds or whatever the meter thinks it was seeing - but not 11.50 volts like 57). From the diagram - I believe I should have 11.50 volts also from 37 with the key on?

I do not know where to go from here. Is there anything that explicitly controls pin 37 differently than pin 57 (except the wire of course) ? Is there a fuse link or the famous ignition switch or anything that is specific to pin 37 ?

I did buy a test light and will start to go through the wiring testing procedure with the fusible links - if I can find all those darn things.

I keep hearing about the famous blue fusible link, but I was assuming that I would not have power on pin 1 if that were bad, but reading another post - it looks like another gentleman had the same issue years ago and it was the blue link or at least one of them. I couldn't tell where it was actually located as the pictures do not show anymore from them being deleted from flikr or photobucket, or etc.

I see I actually have a wire from my solenoid that has a plastic tab on it that says "fusible link". Looked like a little green wire that goes straight down near the bottom and branches into two separate wires.

Problem is - since these cars are getting so old - who knows what repairs have been done and certain color codes will not match anymore from previous repairs.

(Please forgive me if this is in the wrong forum. I thought there were specific tech forums, but just could not see/find them).

Thanks in advance,
Jason
 
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Pins 37 & 57 begin and end at the same places; they are a parallel path from the EEC relay to the computer.
The diagram below only shows 1 wire, but they are 2 separate wires. The reason for this is to make the wiring more flexible. A single 10 gauge wire would be definitely stiffer, harder to bend and more subject to damage from repeated bending due to movement and vibration.

Diagram courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
88-91_5.0_EEC_Wiring_Diagram.gif


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

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

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif


Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif
 
"Pins 37 & 57 begin and end at the same places; they are a parallel path from the EEC relay to the computer."

That was what I was figuring from the diagram but didn't make sense to me since I am seeing 11.50v at 57 and not at 37.

Also - I cannot pull any codes from my test harness.

(I updated the last 4 or 5 paragraphs on my original post).

Thanks,
Jason
 
"Pins 37 & 57 begin and end at the same places; they are a parallel path from the EEC relay to the computer."

That was what I was figuring from the diagram but didn't make sense to me since I am seeing 11.50v at 57 and not at 37.

Also - I cannot pull any codes from my test harness.

(I updated the last 4 or 5 paragraphs on my original post).

Thanks,
Jason
The #37 wire may have a break(s) in it near where it connects to the EEC relay. That would prevent it from passing voltage to the computer wiring connector.

64326d1287785504-fusible-link-burned-up-need-help-87-93-5.0-mustang-fuse-links.gif


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.

Once you get the computer power feed problems fixed, recheck the code dump. You should get an 11 or something. No codes is a definite problem.
 
Well - I am ashamed to admit it - BUT I believe I counted the wrong pin for 37 yesterday.

I do have almost 12v for pins 37 and 57 as well as pin 1 of course.

Since performing old mass-air conversions years ago - I think that the thermactor plug(s) pins got switched so - I was wondering if I unplug the mass air meter and the tad/tab connectors under the hood, can I put a speed density eec on it just to hit the key to run position to see if I hear the fuel pump cut on without messing up anything.

Again - I will still also run my test light through the links next week if need be but just curious if I can do that simple test above with a speed density system as I have 2 or 3 spares.

Thanks in advance,
Jason
 
Fuel Pump Troubleshooting for 87-90 Mustangs

Revised 11-Mar-2014 to add new fuel pump wiring 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.

Underhoodpictures007-01.jpg


Underhoodpictures010.jpg


Turn the ignition switch on when you do this test.
attachment.php


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.

87-90-5-0-mustang-fuel-pump-wiring-gif.88241


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. 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.

attachment.php


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.

attachment.php


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
 
Well - Did some more fuse link probing with light and everything "looked" ok.

Ignition switch kicking in the eec relay and probing the pins 1, 37, and 57 showed 12 V.

Finally said "screw it" and unplugged the mass air meter and plugged in the one of my old 86 VR1 eecs to the harness. Turned the key to on and the fuel fired right up. So - damn A9L processor is bad.

I have had about 13 or 14 mustangs and this is the first time I have ever had a processor go bad. I know it can happen, just never had happened to me before.

Anyway - Want to thank jrichker and tmoss and others for creating fantastic diagnosing procedures and diagrams. Even though I jumped around on them some from some past knowledge and troubleshooting, I have to say that TMOSS's diagrams and JRICHKER's procedures made perfect sense to trace where the problem was.

Thanks again guys,
Jason
 
I have had about 13 or 14 mustangs and this is the first time I have ever had a processor go bad. I know it can happen, just never had happened to me before.

Anyway - Want to thank jrichker and tmoss and others for creating fantastic diagnosing procedures and diagrams. Even though I jumped around on them some from some past knowledge and troubleshooting, I have to say that TMOSS's diagrams and JRICHKER's procedures made perfect sense to trace where the problem was.

Thanks again guys,
Jason
Thank you, I am glad I was able to help.
Joe R.