HELP PLEASE! (1990 Mustang GT)

HONDABUILTSTANG

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May 5, 2011
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I recently put in a new motor, the car ran for about 2 weeks no problems. On my way to church last week i stopped off at a store, went in and when i came out the vehicle would not start and the battery was totally shot. I put a new battery in however when i start the car it will die out as soon as it starts unless i hold the key on. Things i have replaced: Ignition tumbler, ignition switch. Things i have checked: Maf sensor, EGR valve, IAC valve, and tps sensor. I am stumped and do not know what to do now.... Please help any suggestions will help????

FYI: The vehicle was manufactured EFI when i bought it it had been coverted to Carb and i switched it back to EFI. Its a standard 302 block with a crane roller cam, crane rocker arms, an ELdebrock intake, 70mm throttle body and a short ram intake. The engine came out of a 1992 however i used the 1992 wiring harness and PCM, so i dont believe the engine to be the problem.
 
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That's quite a collection of symptoms ya got there. It all sounds like symptoms of an ignition switch problem except the portion about the battery being shot.


So..... Guesses....

Trouble shoot the ignition switch. You shouldn't need to even start the car to do this. There are circuits that are powered with the ignition off, with the switch in accessory mode, and in the start postion. You should be able to shoot most of these from the fuse panel with a trouble light.

The other thing that comes to mind, is the battery problem you mentioned. Pull the starter and have it checked. The possibility exists that the diode in the alternator is bad.
 
Look closely at the wiring harness connectors for the ignition switch. Often the switch will overheat and the connector shell will start to melt. This lets the connectors slip loose and fail to make a good connection.

Diagram courtesy of Tmoss & Stang&2birds
IgnitionSwitchWiring.gif


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info 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