Engine fires but wont stay running

snackman508

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Jun 16, 2019
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31
Lancaster PA
here is some back ground on the motor/ project. the motor 5.0 HO mass air has been sitting for 7ish years. Im putting it in an mazda rx7 so i have modified the harness so its stand alone. when i go to start it will fire up when i start it and as soon as you let off the key it dies every time. it dosnt matter if your holding throttle open or not. its so consistent I feel like its an ecu thing not getting out of a starting mode(if thats a thing). this if my first ford so im new to all of this, but have done my fair share of wrenching. my only idea is i dont have pin 30 hooked up to the clutch peddle switch witch has something to do with start up but not running? any ideas throw them out there i may have over looked something.
 
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jrichker

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Primary ignition circuit not hooked up, coil hot in start mode but not in run mode.
General karthief is right, you have some missing wiring...

Engine fires briefly, but dies immediately when the key is released to the Run position. Crank the engine & when it fires off, pull the small push on connector (red/blue wire) off the starter relay (Looks like it is stuck on a screw). Hold the switch in the crank position: if it continues to run there is a problem with either the ignition switch or TFI module. Check for 12 volts at the red/green wire on the coil with the switch in the Run position. Good 12 volts, then replace the TFI.
See the Ignition switch wiring diagram for more information on the ignition wiring fuse link because it is the next thing to be tested. You will need a Multimeter or DVM and know how to use the Ohms function to check continuity between the red/green wire on the ignition coil and the red/green wire on the ignition switch. Make sure that the ignition switch is in the off position when you do the check. You should see less than 1 Ω (Ohm) between the red/green wire on the coil and the red/green wire on the ignition switch. More than 1 Ω means that the fuse link may have blown open and needs to be replaced. If you get 1 Ω or less means the fuse link is OK and the ignition switch is bad.

The following are diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
88-91_5.0_EEC_Wiring_Diagram.gif


Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_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.


TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

O2 sensor wiring harness

Vacuum diagram 89-93 Mustangs

HVAC vacuum diagram

TFI module differences & pin out

Fuse box layout

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring

93 power window wiring

T5 Cutaway showing T5 internal parts

Visual comparison of the Ford Fuel Injectors, picture by TMoss:

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:

Starter circuit

Alternator diagram for 94-95 Mustangs.
 

snackman508

Member
Jun 16, 2019
2
1
13
31
Lancaster PA
you guys were right on. looked at the wiring on the TFI and i had both red wires wired to the run, not run and start. Swapped some things around and after some coaxing i got it running, not well (its got some 7 year old gremlins to work out) but its runs, kinda. thanks so much for the help
 
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