Car won't start once warmed up

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

1.) Remove push on connector from starter solenoid and turn ignition switch on. Place car in neutral or Park. Remove coil wire from distributor & and hold 3/8” away from 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.) Coil
B.) TFI module
C.) PIP sensor in distributor
D.) ECC relay next to computer - look for 12 volts at the fuel injector red wires
E.) Fuse links in wiring harness - look for 12 volts at the fuel injector red wires
F.) Ignition switch - look for 12 volts at the fuel injector red wires
G.) Computer

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 lower RH corner to ground. See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html for a description of the test connector. 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.) Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect for fuel escaping while 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.

88stangracer said:

Ok the engine will crank up and I cit fine, but thats only cold. Today I started it up, drove it for a bit, got it to operating temp, came home shut it off. I went to crank it back up, well here is some funny SH**. I go to start it, it cranks over and over, well I turn the key back to off, well the car is still trying to crank up, I take the keys completely out! Still it tries cranking up. Weird ? My psycho car man.....anyhow I had to yank the batt. cable to get it to stop. Sooooooooo now what??????????? Thanks.

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Pull the L shaped push on lead off the starter solenoid and if it stops cranking, the problem is in the key switch. If it doesn't stop cranking, replace the starter solenoid.

As for your other problems, get the engine warm and follow the test path I posted. It will find 95% of the no start problems.

88stangracer said:

My 88 5.0 will not start once it reaches normal operating temp. It cranks up great cold. But once it warms up a bit and I turn it off, it just turns the eninge over and over...and over....... but it wont fire up. Im getting spark obviously.

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i hate to ask, but are you sure you are getting spark when it wont start? when you said it is getting spark obviously, do you mean that you know because it cranks over, or because you checked?

i would be leaning toward the electrical side - ignition. first two things i would check:
check your coil when it wont start. also, i think the PIP goin out can cause a no start when hot condition.

my two cents worth. good luck.

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i had the same problem, and it ended up being a loose connection in the power wire for the 6al where i had a wire connector and didnt pinch it hard enough. It may not be the box.

same problem

i had the same problem...turns out after a month of messing with it, bringing it to shops i bought a repair manual for my car and figured out it was my "hull effect sensor" aka stator aka distributor pick-up...changed that out and she works fine...
to get me through until i could get it replaced, i had a can of contact cleaner in my car, whenever it acted up i would get out, open the distributor and spray the sensor with the spray to cool it down and it would start right up....

fuel issue due to sensor

my 5.0 did that for months, got worse and worse ...

found a bad coolant sensor .. it was giving the computer a "cold engine" signal when the engine was hot and therefore not proper amount of fuel ...

took sensor out and checked voltage while heating in a pot of water .. it was dead ...