Help me fix and make $50!

5.0fox said:

Matt what arte you doing right now?

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missed your call, PM'd you back, or call me back.

+1 for the coil.

For a bonus, check the ignition module mounted on the distributor...

I'd look at spark over fuel.

Lastly, any custom intake, CAI or air filter?

I had very similar heat soak problems and replacing the ignition module fixed it!

i would try the electronic ignition switch on the side of the steering column

check your engine ground at the block and the thick wire goin to the starter and see if the copper is dirty or corroded

daviszx3 said:

i would try the electronic ignition switch on the side of the steering column

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If it were the ignition switch, it wouldn't crank. Same thing with the starter wire. I would check all of your ground wires, though.

Do the spark plugs have any gas on them after you try to start it?

Mustank said:

If it were the ignition switch, it wouldn't crank. Same thing with the starter wire. I would check all of your ground wires, though.

Do the spark plugs have any gas on them after you try to start it?

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the ignition switch at the key can go bad, and it'll just crank and won't start. It's happened on just about every fox I've had. the switch seperates and begins to fall apart. It looses some of it's contacts, and won't turn the fuel pump on, but will engage the starter.

5.0fox said:

Ignition switch and tumbler are ordered because they are a little screwed up anyway.
plugs do get wet while cranking. Ill check all grounds including injector ground in the morning.

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Don't waste your time looking for an injector ground in the wiring harness because there isn't one.
The injectors have 12 volts on them anytime the ignition switch is in the run postion. The computer
provides a switched ground to trigger the injector.

The orange wire that bolts to ground in the injector harness is the O2 sensor ground.

Remember that the computer does not source power for any actuator or relay, but provides the ground necessary to complete the circuit.
That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

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/

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel pump, alternator, ignition & A/C wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Computer, actuator & sensor wiring
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Fuse panel layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Vacuum routing
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

ignition control module

what do the computer codes tell you?

why won't codes display?? if that's the case, jumper it under the hood, and hook up a light there, and it'll flash for the codes

Computer will not go into diagnostic mode 86-90 model 5.0 Mustangs

How it is supposed to work:
The black/white wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the
computer into self test mode. If this ground is bad, none of the sensors mentioned will work
properly. That will severely affect the car's performance. You will have hard starting, low power
and drivability problems. Since it is a dedicated ground, it passes through the computer on its
way to the computer main power ground that terminates at the battery pigtail ground. It should
read less than 1.5 ohms when measured from anyplace on the engine harness with the battery
pigtail ground as the other reference point for the ohmmeter probe.

What sometimes happens is that the test connector black/white wire gets jumpered to power
which either burns up the wiring or burns the trace off the pc board inside the computer.
That trace connects pins 46 to pins 40 & 60. Only an experienced electronics technician can open
the computer up & repair the trace if it burns up and creates an open circuit.

The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering
it to power can produce unknown results, including damage to the computer. The ohm test
simply verifies that there are no breaks in the wiring between the test connector and the computer input.

How to test the wiring :
With the power off, measure the resistance between the computer test ground
(black/white wire) on the self test connector and battery ground. You should see less than
1.5 ohms.



If that check fails, remove the passenger side kick panel and disconnect the computer
connector. There is a 10 MM bolt that holds it in place. Measure the resistance between
the black/white wire and pin 46: it should be less than 1.5 ohms. More that 1.5 ohms is a
wiring problem. If it reads 1.5 ohms or less, then the computer is suspect. On the
computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than
1.5 ohms. More that that and the computer’s internal ground has failed, and the computer
needs to be replaced.

If the first ground check was good, there are other wires to check. Measure the
resistance between the STI computer self test connector (red/white wire) and pin 48 on
the computer main connector: it should be less than 1.5 ohms. More that 1.5 ohms is a
wiring problem

The following is a view from the computer side of the computer connector.


Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the black/white wire goes. Almost every
sensor on the engine except the MAF is connected to it.


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

Have you tried switching computers? Could the computer be getting too hot? I've seen this before on an older Taurus ('91), it had the same symptoms.
Since you have a weak spark, wet plugs means you have fuel, you obviously have air since it works any time when it is cold.
You have already swapped the Hall Effect, and Ignition module. Also, checked a bunch of other stuff, why not swap the computer? Just take the connector loose and connect it to another computer from a friend, junk yard, whatever, lay it in the passenger's floorboard, and see if the problem goes away.