Turns over but doesn't Crank Please Help

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Revised 26-Jul-2008 to add new links to AutoZone ignition wiring for 86-88 model cars

All text applies to all models unless stated otherwise.

Note: 94-95 specific changes are in red

1.) Remove push on connector (small red/blue wire) from starter solenoid and turn ignition switch on. Place car in neutral or Park and set the parking brake. Remove the coil wire from distributor & and hold it 3/8” away from the engine block. Jumper the screw to the big bolt on the starter solenoid that has the battery wire connected to it. You should get a nice fat blue spark.
Most of the items are electrical in nature, so a test light, or even better, a voltmeter, is helpful to be sure they have power to them.

No spark, possible failed items in order of their probability:
A.) MSD or Crane ignition box if so equipped
B.) Coil
C.) TFI module
D.) PIP sensor in distributor. The PIP sensor supplies the timing pulse to trigger the TFI and injectors. See paragraph 5A - a noid light will tell if the pip is working by flashing when the engine is cranking.
E.) No ECC or computer power - ECC or computer relay failure
86-93 models only: ECC relay next to computer - look for 12 volts at the fuel injector red wires
94-95 models only: EEC or PCM power relay in the constant control relay module. Look for 12 volts at the fuel injector red wires.
F.) No ECC or computer power - fuse or fuse link failure
86-93 models only: Fuse links in wiring harness - look for 12 volts at the fuel injector red wires. All the fuse links live in a bundle up near the starter solenoid.
94-95 models only: 20 amp EEC fuse in the engine compartment fuse box. Look for 12 volts at the fuel injector red wires.
G.) Ignition switch - look for 12 volts at the ignition coil red/lt green wire. No 12 volts, blown fuse link or faulty ignition switch. Remove the plastic from around the ignition switch and look for 12 volts on the red/green wire with the switch in the Run position. No 12 volts and the ignition switch is faulty. If 12 volts is present in the Run position, then the fuse link is blown.
94-95 models only: Check inside fuse panel for fuse #18 blown – 20 amp fuse
H.) Bad or missing secondary power ground. It is located between the back of the intake manifold and the driver's side firewall. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges.
I.) Missing or loose computer power ground. The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next to the starter solenoid where the wire goes into the wiring harness
J.) Computer
K.) 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 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. No 12 volts, replace the ignition switch.

See the following links for wiring diagrams...

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model cars
Computer/fuel pump/ignition wiring diagram, 86 model http://www.autozone.com/images/cds/gif/large/0900823d80167158.gif
Computer/fuel pump/ignition wiring diagram, 87 model http://www.autozone.com/images/cds/gif/large/0900823d8016715e.gif
Ignition wiring diagram, 87 model http://www.autozone.com/images/cds/gif/large/0900823d8016715f.gif
Computer/fuel pump wiring diagram, 88 model http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif[
Ignition wiring diagram, 88 model http://www.autozone.com/images/cds/gif/large/0900823d80167163.gif

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model cars
Computer/fuel pump/ignition wiring diagram, 89-90 cars http://www.autozone.com/images/cds/gif/large/0900823d8019595f.gif
Computer/fuel pump/ignition wiring diagram, 91-93 cars
http://www.autozone.com/images/cds/gif/large/0900823d80195960.gif

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp for 94-98 model cars

2.) Spark at coil wire, pull #1 plug wire off at the spark plug and check to see spark. No spark, possible failed items in order of their probability:
A.) Moisture inside distributor – remove cap, dry off & spray with WD40
B.) Distributor cap
C.) Rotor
D.) Spark Plug wires
E.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil

3.) Spark at spark plug, but no start.
Next, get a can of starting fluid (ether) from your local auto parts store: costs a $1.30 or so. Then pull the air duct off at the throttle body elbow, open the throttle, and spray the ether in it. Reconnect the air duct and try to start the car. Do not try to start the car without reconnecting the air duct.

Two reasons:
1.) If it backfires, the chance for a serious fire is increased.
2.) On Mass Air cars, the computer needs to measure the MAF flow once the engine starts.
If it starts then, you have a fuel management issue. Continue the checklist with emphasis of fuel related items that follow. If it doesn’t, then it is a computer or timing issue: see Step 4.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the EEC test connector and jump the connector in the Upper RH corner to ground. The EEC connector is near the wiper motor and LH hood hinge.


If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. Beware of fire hazard when you do this. In a pinch, you can use a tire pressure gauge to measure the fuel pressure. It may not be completely accurate, but you will have some clue as to how much pressure you have. If you have any doubts about having sufficient fuel flow/pressure, rent a fuel pressure test gauge from the auto parts store. That will tell you for sure if you have adequate fuel pressure.


4.) No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – Coupe & hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) 86-90 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay.
91-93 models only Blown fuse link in wiring harness. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
The fuse links for all model years 86-93 live in the wiring harness near the starter solenoid.
94-95 models only: 20 amp fuel pump fuse in the engine compartment fuse box. Look for 12 volts at the Dark green/yellow wire on the constant control relay module.
F.) Engine seem to load up on fuel and may have black smoke at the tailpipe. Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect for fuel escaping while the pump is running. If fuel is coming out the vacuum port, the regulator has failed. Check the regulator vacuum line for fuel too. Disconnect it from the engine and blow air though it. If you find gas, the regulator has failed.

5.) Fuel pressure OK, the injectors are not firing.
A.) A noid light available from any auto parts store, is one way to test the injector wiring.
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 injector is firing.
B.) I like to use an old injector with compressed air applied to the injector where the fuel rail would normally connect. I hook the whole thing up, apply compressed air to the injector and stick it in a paper cup of soapy water. When the engine cranks with the ignition switch on, if the injector fires, it makes bubbles. Cheap if you have the stuff laying around, and works good too.
D.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on.
E.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at the rear of the upper manifold).
F.) No power and the 10 pin connections are good: look for broken wiring between the orange/black wire on the ECC relay and the red wire for the 10 pin connectors.
G.) TPS voltage exceeds 3.7 volts with the throttle closed. This will shut off the injectors, since the computer uses this strategy to clear a flooded engine. Use a DVM, a pair of safety pins, and probe the black/white and green wires to measure the TPS voltage.
On a 94-95 Mustang, probe the black/white and grey/white wires to measure the TPS voltage.
It should be .5-.99 volts with the key on, engine not running. Note that if the black/white wire (signal ground) has a bad connection, you will get some strange readings. Make a second measurement using the battery post as the ground to eliminate any ground problems. If the readings are different by more than 5%, you may have a high resistance condition in the black/white signal ground circuit.

6.) Spark & fuel pressure OK.
A.) Failed IAB or improperly set base idle (no airflow to start engine). Press the throttle ¼ way down and try to start the car. See the "Surging Idle Checklist for help with all your idle/stall problems.
B.) Failed computer (not very likely)
C.) Engine ignition or cam timing off: only likely if the engine has been worked on recently).
D.) Firing order off: HO & 351 use a different firing order from the non HO engines.
HO & 351W 1-3-7-2-6-5-4-8
Non HO 1-5-4-2-6-3-7-8
E.) No start when hot - Press the throttle to the floor & try starting it if you get this far. If it starts, replace the ECT.
F. ) Engine that has had the heads off or valves adjusted. Do a compression test to make sure the valves are not adjusted too tight. You should have a minimum of 90 PSI on a cold engine.

You should not have 12 volts on the ground wire to the coil.

Ditch the MSD first by bypassing it. That eliminates one of the possible problem areas.
Then look for 12 volts at the ignition coil red/lt green wire with the ignition switch in the Run position.
No 12 volts and you have a problem with the ignition switch, ignition switch wiring or the fuse link in the ignition coil power feed.

techsan said:

Sorry i was unclear in my last post. I have twelve volts to the light green and red wire coming off of the harness, but they are connected to the small red wire, and the small black wire of the MSD 6AL box. I have .08-.09 volts on both ends of the coil with the key in the on position. With the key out of the car, i have 0 voltage at the coil. Any ideas would be greatly appreciated.

Click to expand...

Did you test the modulated ground pulse to the coil? This is where I generally start if there's a no-spark condition.

a car won't start for one of 3 reasons. fuel, air or fire. you need to know first if the plugs are firing. take a flat head screw driver and put it inside the first plug wire after disconnecting it from the plug. then set it close enough to arch against the firewall or somewhere.
crank it.
if it archs it ain't the coil. then you can move onto fuel and air

coil. try that, they are cheap.

techsan said:

As the car is set up now, there is no green wire going to the ignition coil. The only wires going to the coil are an orange wire from the MSD to the positive side of the coil, and a black wire from the negative of the coil back to the MSD. I would love to set the car up with the stock ignition, but i don't know which wires should be on the coil. There is a red wire with a light green stripe that is near the coil. It is connected to a red wire that runs back to the MSD. Is this the wire i need to check for voltage? It has 12 volts when the key is in the on position. Can i connect this red wire with a green stripe to the positive side of the coil? If i do that can i ground the negative side of the coil to the negative side of the battery to bypass the MSD box? Or, does anyone know which wires should be connected to the coil for the stock ignition set up. I dind't wire the MSD, and i would love to take taht out of the equation.

How do i check the modulated ground pulse to the coil?

Sorry for the long posts, just trying to give as much information as possible.

Click to expand...

To restore the ignition, the red/lt green wire goes to the positive side of the coil. This wire has constant key-on 12 volts.

Dk Green/Yellow goes to the negative side of the coil. This ground is pulsed/modulated by the EEC and TFI to energize the coil.

The coil's terminals are probably labeled + and -

Once you have the stock wiring restored (MSD bypassed), put a test light across the two wires going to the coil (that you just fixed). Crank the engine, noting if the test light flashes.

MSD wiring: (MSD stands for May Suddenly Die...)

Go back to the checklist. Start at the top and work your way down. It was designed to eliminate
the things that work and leave you with the things that don't work. It will save you time and
money and keep you from throwing parts at a problem in a vain effort to fix it.

Herer is some more ignition specific help since most people seem to have problems with electrical stuff...

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 links for wiring diagrams...

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model cars
Computer/fuel pump/ignition wiring diagram, 86 model http://www.autozone.com/images/cds/gif/large/0900823d80167158.gif
Computer/fuel pump/ignition wiring diagram, 87 model http://www.autozone.com/images/cds/gif/large/0900823d8016715e.gif
Ignition wiring diagram, 87 model http://www.autozone.com/images/cds/gif/large/0900823d8016715f.gif
Computer/fuel pump wiring diagram, 88 model http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif[
Ignition wiring diagram, 88 model http://www.autozone.com/images/cds/gif/large/0900823d80167163.gif

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model cars
Computer/fuel pump/ignition wiring diagram, 89-90 cars http://www.autozone.com/images/cds/gif/large/0900823d8019595f.gif
Computer/fuel pump/ignition wiring diagram, 91-93 cars
http://www.autozone.com/images/cds/gif/large/0900823d80195960.gif

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