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91 mustang fires then shuts off

Marcos Aponte
New User
Posts: 1
Joined: 04/14
Posted: 04/16/14 08:55 PM

Hello I have a 91 mustang GT this whole problem started when the degrees dropped to single digits. The parts I've changed - mass air sensor  - tfi module - fuel filter - spark plug wires - starter - solenoid. The tfi module I replaced last and the car started right up so I let it warm up for 20 mins as I'm walking out to take it for a test drive it cuts off I try to start it back up and it fires and shuts  right off anyone have this problem before ???  

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New User
Posts: 16
Joined: 10/13
Posted: 04/17/14 07:50 AM

do you own a test light?????

HF 30779 Zpsc0772e7e

there are 2 connectors into the ignition coil...  a green wire.. and one with RED in it..

stick the PROBE end into the coil connector on the red wire side. coil positive..

unplug the small push on connector at the starter relay..  so the starter does NOT crank when you operate the key for this test..

ground the clip..   sit in the drivers seat and slowly turn the key on.. the test light should lite up.. turn the key to the crank position..  it should still light up.. release the key.. it should still be bright..  you should NOT have any dropouts until you turn the key OFF..

this tests the ignition switch circuit...

next .. do the same test for the idle air control solenoid power.. unplug the idle air control solenoid and figure out which side is hot with the key on..  

the idle air solenoid power is controlled by the EFI main relay..  it also powers most of the other fuel injection items on the motor..

if you have a timing light.. lets try another test..  use tape or a rubber band to squeeze the trigger into the ON position.. so it flashes all the time when hooked up..

hook it up over the coil wire..  instead of a spark plug wire.. we are not setting timing we are watching the ignition output..   this is going to require you standing next to the car.. or operating the key with the timing light under the wiper arm.. so you can see the flashing.. see if when the engine stalls.. if the light stops flashing before the engine comes to a stop.. this is usually better if you have it up at fast idle.. a scrap of cardboard.. under the throttle speed screw.. to hold the throttle part way open..  

if it stalls and the light goes out before the engine stops running..

reach in and unplug the PIP or sprout.. the timing plug you undo to set timing.. start it back up.. that takes ignition control away from the ECM and leaves it only with the TFI module and ignition switch..  and pickup electronics in the distributor..

perform this test a second time..

if you failed to use Dielectric tune up grease under the module..  you will have an overheating TFI module and it will be damaged..  the dielectric tune up grease is a thermal transfer compound..  takes the heat created by the power transistor switching operation and transfers it to the heat sink or distributor housing..  without it. the module overheats.. traces lift off the circuit board and the whole thing fails..

there is a chance its the ECM also.. you can remove and open it carefully.. look for cracked solder joints..  

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