? about Ohms & EEC

[stangman16]

My injectors are not firing on my '66 EFI conversion stang and I'm following along jrichker's instructions to test the ECU wiring.

Next Check the fuel injector wiring end to end. Each fuel injector has a red
wire (power) and an non-read wire (computer controlled ground). Set the
multimeter to low ohms and measure each non red fuel injector wire from
the fuel injector connector to the matching pin on the computer connector.
You should see less than 2 Ohms. More than that means a bad connection
or bad wiring.

I have a question about the Ohms readings I'm getting when I hook up the ground wire at the injector and where it runs to at the computer connector. I get an ohm's reading of 0.9 - 1.1 and with the prongs disconnected and touching I get the same thing... does this indicate that my wiring is good?

3.) Set the multimeter to low scale Ohms and measure between the
computer ground located below the computer and the suspect fuel injector
pins. You should see greater than 100 K Ohms resistance. If you see less
than 100 Ohms, the wiring between the injector and the computer has a
short to ground and needs service. Check the harness and look for damage,
kinks or frayed spots.


Where is the computer ground to where I can check this? Do I use PIN 60 ? When I plug into pin 60 and the ground wire for the injector, the multimeter just shows the infinity symbol (rather just the #1) I'll have to go back out and double check that, but am I doing this correctly?

I'm trying to be 100% sure the A9L computer is shot before I go buy another one, since this is an EFI conversion I'm not sure if it worked when I had purchased it.

 

[jrichker]

Since I wrote the test path, I guess I had better respond to your post.

Measure the resistance of the wire form the non red wire on the injector connector to the pin on the computer connector. You will need to disconnect the computer to do this. On 86-93 Mustangs, the computer is located under the passenger side kick panel. Disconnect the computer by loosening the 10 MM bolt in the center of the wiring connector.

1. 
   Injector # Wire color computer pin
   [1] tan 58
   [2] white 59
   [3] brown/yellow 12
   [4] brown/lt blue 13
   [5] tan/lt blue 14
   [6] lt green 15
   [7] tan/orange 42
   [8] lt blue 52

The end to end resistance of each one of these wires should be less than 2.0 ohms. The resistance between each wire and ground with the computer and injector disconnected should be 1 megohm or greater. Use the engine block, battery negative terminal or car chassis as a ground. Be sure not to hold the metal probe tips with your hands. If you do, the readings will be inaccurate.

Re-connect the computer and its connector to make the next measurements.

Before you replace the computer, make your measurements at the back of the computer connector to insure that you have power and ground. Pins 37 & 57 should have power with the ignition switch in the Run position.

Check the red wire on ech injector for 12 volts. No 12 volts and you need to back up and study the wiring diagram some more. Check the 12 pin connectors and the EEC relay for proper operation.

With the ignition switch is the Off position,
Pins 40 & 60 should have less that 1.0 ohms between them and any good ground on the body.

 

[stangman16]

Measure the resistance of the wire form the non red wire on the injector connector to the pin on the computer connector. You will need to disconnect the computer to do this. On 86-93 Mustangs, the computer is located under the passenger side kick panel. Disconnect the computer by loosening the 10 MM bolt in the center of the wiring connector.

1. 
   Injector # Wire color computer pin
   [1] tan 58
   [2] white 59
   [3] brown/yellow 12
   [4] brown/lt blue 13
   [5] tan/lt blue 14
   [6] lt green 15
   [7] tan/orange 42
   [8] lt blue 52

The end to end resistance of each one of these wires should be less than 2.0 ohms.

Did the above, and it came to 0.9, which is the same reading i get if I just connect both prongs together.

The resistance between each wire and ground with the computer and injector disconnected should be 1 megohm or greater. Use the engine block, battery negative terminal or car chassis as a ground. Be sure not to hold the metal probe tips with your hands. If you do, the readings will be inaccurate.

Did the above, and did not get any reading at all, I tried all 3 sources for the ground. The multimeter just displays the infinity 0.L sign. I have one of the multimeter wires on the battery negative, and the other end at the non-red wire of the injector harness...

Re-connect the computer and its connector to make the next measurements.

Before you replace the computer, make your measurements at the back of the computer connector to insure that you have power and ground. Pins 37 & 57 should have power with the ignition switch in the Run position.

Check, almost the same voltage as when I checked the battery voltage.

Check the red wire on ech injector for 12 volts. No 12 volts and you need to back up and study the wiring diagram some more. Check the 12 pin connectors and the EEC relay for proper operation.

Check, power to red wire at the injectors.

With the ignition switch is the Off position,
Pins 40 & 60 should have less that 1.0 ohms between them and any good ground on the body.

Check, .5 Ohm for each.

 

[stangman16]

For the one where I didn't get a reading, if I put one prong on the chassis and the other on the red wire of the injector, I get about 16 M ohms, but no reading on the ground wire that runs to the ECM

 

[jrichker]

All your readings look good. The red wire to chassis test isn't important if you have power to the red wire.

 

[HISSIN50]

I'm not sure if it applies (and I admit I didnt read all of this too closely, so I might be redundant), but ensure the TPS is not reading more than ~3.71 volts with the throttle closed. If it reads that high or more, the puter shuts off injector pulsing.

Good luck.

 

[stangman16]

All your readings look good. The red wire to chassis test isn't important if you have power to the red wire.

even though I didn't get a reading for the 1 megohm?

 

[stangman16]

I'm not sure if it applies (and I admit I didnt read all of this too closely, so I might be redundant), but ensure the TPS is not reading more than ~3.71 volts with the throttle closed. If it reads that high or more, the puter shuts off injector pulsing.

Good luck.

Will do, if that turns out allright, I guess I better find a new A9L.

 

[stangman16]

Okay, finally got around to getting a new ECM. Replaced and the car still does not start. The noid light does not flash.... what's next?

 

[stangman16]

Oh, I just went to check the voltage at pins 37 & 57 with the EEC plugged in.

37 = 11.38V
57 = 0.66V

I unplugged the Brown colored Relay and they both read 1.66V afterwards... I'm going to go pick up a new relay - I hope Advance auto has one.

 

[HISSIN50]

Oh, I just went to check the voltage at pins 37 & 57 with the EEC plugged in.

37 = 11.38V
57 = 0.66V

I unplugged the Brown colored Relay and they both read 1.66V afterwards... I'm going to go pick up a new relay - I hope Advance auto has one.

It's been awhile, but don't 57 and 37 tie together? Is there an open in the wiring?

Good luck.

 

[jrichker]

It's been awhile, but don't 57 and 37 tie together? Is there an open in the wiring?

Good luck.

Both 37 & 57 tie together and shold read the same voltages.

Diagram courtesy of Tmoss & Stang&2birds

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.

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

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

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

 

[stangman16]

Thanks HISSIN50 & jrichker, I will check into the wiring again to see why they do not match when the relay is plugged in. I haven't gotten the new relay yet - the one currently in there looks old and rusty a little, so it's on my replace list. I just haven't time yet, gotta run.

Do you think that is the reason as to why the injectors would not fire though? Strange enough the injectors are getting the 12V that they should be... so is it just not supplying necessary power to the EEC to permit the ground connection needed? (i'm one of those - 'how does it work' kind of people)

 

[jrichker]

Thanks HISSIN50 & jrichker, I will check into the wiring again to see why they do not match when the relay is plugged in. I haven't gotten the new relay yet - the one currently in there looks old and rusty a little, so it's on my replace list. I just haven't time yet, gotta run.

Do you think that is the reason as to why the injectors would not fire though? Strange enough the injectors are getting the 12V that they should be... so is it just not supplying necessary power to the EEC to permit the ground connection needed? (i'm one of those - 'how does it work' kind of people)

Automobile computers use current sink technology. They do not source power to any relay, solenoid or
actuator like the IAC, fuel pump relay, or fuel injectors. Instead the computer provides a ground path for
the positive battery voltage to get back to the battery negative terminal. That flow of power from positive
to negative is what provides the energy to make the IAC, fuel pump relay, or fuel injectors work. No ground
provided by the computer, then the actuators and relays don't operate.

One side of the any relay/actuator/solenoid in the engine compartment will be connected to a red wire that
has 12-14 volts anytime the ignition switch is in the run position. The other side will have 12-14 volts when
the relay/actuator/solenoid isn't turned on. Once the computer turns on the clamp side, the voltage on the
computer side of the wire will drop down to 1 volt or less.