Wont Start Wont Go Into Diagnostic Mode

[stykthyn]

Following up on my bad fuel pump thread I had O'reilly's replace my new not working distributor/tfi module with a new working distributor/tfi module. Life was grand until I went to leave work this morning and the car wouldnt start. Fuel pump wouldnt prime. I figured it was no big deal and an extension of the problems I had been experiencing for the last few months. so I go back over the fuel pump list jrichker had posted and everything seemed good. slapped the code reader on and the ecu will not go into diagnostic mode. my question is will a dead eec relay give the symptoms I am seeing? right now I turn the key to the acc position and I get a pathetic beep from the dash. I jumper the fuel pump and it runs. I checked for 12v at the injectors and its there and I have 12v at the inertia switch.

 

[jcgafford]

mine did something like that a while back. after many hours of testing everything and retesting it came down to a bad computer. hope thats not your case.

 

[stykthyn]

Already prepared for that eventuality. Ive tested everything except the eec relay which is next on my list. Just have to dig it out from it's home.

 

[jrichker]

If you have good 12 volts on the injector power wires, then the EEC realy is working like it should. The same 12 volts on those injector power wires feed the power input to the computer.

Diagram courtesy of Tmoss & Stang&2birds

That means the computer has died...

But...before you bury it, check the power ground to be sure it isn't causing problems.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972

Correct negative battery ground cable.

The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.



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

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

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 & pinout
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

 

[stykthyn]

Alright then i guess that confirms it. Hopefully this will be the last type of these posts that i make.

 

[jcgafford]

kinda figured... that sucks.