Cranks, No start, Orange spark @ coil....?

Aliate X said:

I did a test and Im getting .001 resistance between the neg side of the coil and the TFI, are there any other fuses I could look for?



edit - I just tried it with the key in the run position and Im getting between 7.8 and 8.2 ohms, would the fuse be blown?

and where exactly are the inline fuses?

Click to expand...

Be sure you have both sides of the harness disconnected when you do a continuity test. Set your meter to the lowest macro Ohms scale (i.e., 200 Ohms) or post results in Ohms.

Aliate X said:

I just found that the little wire coming off of the starter solenoid (its red/lt green or blue, cant really tell) it like plugs onto the little stud at the top of the solenoid, it was burned through on the coil, so Im guessing maybe it grounded out and blew a fuse? Where exactly are the inline fuses?

Click to expand...

This is just the trigger for the starter solenoid. It doesnt affect coil performance (so long as it works well enough for the engine to turn over).

There is a start input on your TFI that tells the module to send cranking spark. The source for this is before that burned connector of yours. Do be sure that TFI input is indeed 12V.

I dont have inline fuses on my wiring harness so I can't answer that question. We have fusible links stock.
The links are mostly located just off the solenoid. They look like fat parts of the wire. When they burn, they can get soft and gooey (like gum stretching) when you pull on them.

How the TFI ignition works in 86-93 model Mustangs:

Tools needed: DVM, noid light, safety pin.

Theory of operation:
The TFI ignition in 86-93 Mustangs has 4 main components: the ignition switch, the coil,
the TFI module and the PIP sensor inside the distributor.

The ignition switch gets power from the two yellow wires that are supplied power
by a fuse link located in the wiring harness that connects to the starter solenoid.

Diagram courtesy of Tmoss & Stang&2birds


The coil is mounted on the driver’s side strut tower on most EFI Mustangs. It gets power
from a red/green wire and a brown/pink wire from the ignition switch. That wire from
the ignition switch feeds a 20 gauge blue fuse link that connects to the red/green wire.
The fuse link protects the wiring and the ignition switch, since the fuse link for the two yellow
power supply wires has a much higher current rating. Without the smaller fuse link protecting
the smaller wiring used in the ignition circuit, a short there would cause the red/green wire
to overheat and burn up.

The TFI module is mounted on the side of the distributor and supplies the ground for the coil.
Every automotive power supply circuit uses the ground as the return path to carry power back
to the negative side of the battery. The TFI switches the tan/yellow wire coming from the coil
to ground. It gets power from the red/green wire when the ignition switch is in the Run position.
The red/lt blue wire supplies a signal to turn on more power (dwell time) when the engine is cranking.
The trigger signal comes from the PIP sensor when cranking and the computer when the
engine is running. The SPOUT jumper plug enables computer controlled spark advance.
When the SPOUT is removed, spark advance is locked at the setting determined by the
mechanical position of the distributor.

The PIP sensor is in the bottom of the distributor under the shutter wheel. It is a Hall effect
magnetic sensor that senses a change in the magnetic field when one of the slots in the
shutter wheel uncovers the sensor. Then it supplies a pulse that triggers the TFI module
to provide a ground to the ignition coil. A bad PIP will often set code 14 in the computer and
cause hot start problems. Replacing the PIP sensor requires removal of the distributor and pressing
the gear off the distributor shaft to expose the sensor. For most people, a remanufactured
distributor ($55-$75) is the solution, since they may not have access to a press.

Troubleshooting the ignition system – no spark or weak spark. All the tests are done with
the ignition switch in the Run position unless specified otherwise. A safety pin may be used
to probe the wiring connectors from the back side.
1.) Check for 12 volts at the yellow wires on the ignition switch. No 12 volts and
the fuse link near the starter solenoid has open circuited.
2.) Check for 12 volts on the red/green and brown/pink wires coming out of the ignition switch.
No 12 volts, replace the ignition switch.
3.) Check for 12 volts at the ignition coil. No 12 volts and the blue 20 gauge fuse link has open circuited.
4.) Check for 12 volts at the red/green wire on the TFI module. No 12 volts and you have wiring problems.
5.) Remove the small red/blue wire from the starter solenoid (looks like it is stuck on a screw).
This is a safety measure to keep the engine from turning while you are making measurements.
Have a helper turn the ignition switch to Start and look for 12 volts on the red/lt blue wire on the TFI module.
No 12 volts and you will have starting problems, but push starting the car will work OK. No 12 volts,
replace the ignition switch. Be sure to reconnect the red/blue wire to the starter when you finish.
6.) A noid light available from any auto parts store, is one way to test the PIP pulse. The computer uses
the PIP signal to trigger the fuel injectors. The noid light plugs into the fuel injector harness in place
of any easily accessible injector. Plug it in and it will flash if the PIP is working. No flash from the
noid light and the PIP is suspect. To confirm the PIP is being the source of the non flashing
noid light, look for 12 volts on the red injector wiring. Good 12 volts and no flashing noid light means the PIP has failed.
7.) Remove the SPOUT plug from the harness and try to start the engine. If it starts,
replace the PIP. This is a common no start condition when the engine is hot.
8.) The TFI module is a go/no go item when you have a no spark/weak spark condition on a cold engine.
It either works or it doesn’t.
The TFI failure mode on a running car is usually a high speed miss on a warm engine. Many auto parts
stores will test your TFI module for free. Bring along a hair dryer to get it hot while testing it and
run several test cycles, since it often gets weak when it heats up.
The coil is somewhat more difficult to pinpoint as a problem. A good coil will make a nice fat blue spark 3/8”-1/2” long.
The problem is that one person’s perception of a fat blue spark looks like may not be accurate enough to spot a weak coil.
The coil is cheap enough ($13-$16) that having a known good working spare might be a good idea.

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

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