Cranks OK, but No Start Checklist for Fuel Injected Mustangs
Revised 30-Jul-2006 to include pip diagnostic help
All text applies to all models unless stated otherwise.
Note: 94-95 specific changes are in red
1.) Remove push on connector 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. See paragraph 3A - 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.
H.) Computer
See the following links for wiring diagrams...
http://www.autozone.com/servlet/UiBr...3d8016713c.jsp for 79-88 model cars
Computer/fuel pump/ignition wiring diagram, 86 model
http://www.autozone.com/images/cds/g...3d80167158.gif
Computer/fuel pump/ignition wiring diagram, 87 model
http://www.autozone.com/images/cds/g...3d8016715e.gif
Computer/fuel pump/ignition wiring diagram, 88 model
http://www.autozone.com/images/cds/g...3d80167162.gif
http://www.autozone.com/servlet/UiBr...3d8019595a.jsp for 89-93 model cars
Computer/fuel pump/ignition wiring diagram, 89-90 cars
http://www.autozone.com/images/cds/g...3d8019595f.gif
Computer/fuel pump/ignition wiring diagram, 91-93 cars
http://www.autozone.com/images/cds/g...3d80195960.gif
http://www.autozone.com/servlet/UiB..._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 ECC test
connector and jump the connector in the Upper RH corner to ground.
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 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.
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.) 86-93 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue
wire on the fuel pump relay. The fuse links 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.) Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect
for fuel escaping while the pump is running.
Fuel pressure OK, the injectors are not firing.
A.) A Noid light available from Autozone, is one way to test the injector wiring.
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.
a.) Pull an injector wire connector off and look for 12 volts on the red wire when the
ignition switch is on.
b.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at
the rear of the upper manifold).
c.) 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.
4.) Spark & fuel pressure OK.
A.) Failed IAB (no airflow to start engine). Press the throttle ¼ way down and try to start the car.
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.
Computer will not go into diagnostic mode
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. 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 it 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
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
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89 Mustang GT, 308, Tremec 3550, King Cobra clutch, FMS Quadrant, Aluminum driveshaft. FMS SS headers, MAC Cat H pipe, 3 chamber Flows, Steeda caster-camber , 73 MM front brake calipers, Turbo Coupe rear end /3.55 gears. 155 LPH FP, Kirban FPR, 70 MM Ford MAF. Explorer/GT40 intake, 65 mm TB, 3G alternator, GDI 3 core radiator.
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#6 10-17-06, 11:17 AM
chobracobra
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