Engine 93 5.0 Looking for suggestions. After Hiway driving car stalls.

senorpavo said:

Hey everyone. Just looking for some ideas as to what may be the issue. After driving on the hiway for a few hours then coming back into town, the car will hesitate and stall when sitting at a traffic light. If the car sits for a few hours it runs fine again. I did have the fuel pressure tested once when it happened and it was at like 8psi. We put a new pump on it and drove home but the car still has this condition. So it wasn't the pump.

New CPU
New TPS
New Ignition Module
New Plugs / Wires / Coil
New Fuel Pump

Could an overheated fuel line cause this? A bad fuel return? I'm at a loss and open to suggestions. It may not even be the fuel I just know that one time the pressure tested low. When it is colder and running fine the fuel pressure is at like 32psi at idle(regulator hooked up).

Click to expand...

Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 38-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC test connector and jump the connector in the Upper RH corner to ground.



Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.

I've never heard of overheated fuel lines on a foxbody, ever.
Buy a 90 degree elbow and a liquid filled gauge and mount it permanently to the Schrader valve.
The normal culprits for heat related no starts is the tfi and the pip.
You replaced the tfi but you didn't say what brand you used, chain store tfi's are crap, it's not if, it's when it will fail.

IMO for ignition parts you can only use factory ford original for the tfi, distributor and coil.

senorpavo said:

It has a new pump. Same issue.
I checked fuel pressure regulator and it appears to be working fine and I have checked pressure and it is good, at least when it is cold. I suppose I'd need to test the fuel pressure when it is having this problem. The only time I did that the psi was at 8 (before the new pump).

Assuming that this is the same exact issue, as it seems to be. Could it be that the fuel lines are getting too hot? After a long cruise and I do live in the tropics where it is hot, sitting at idle would increase under hood temps by a lot. If the fuel lines are close to the exhaust at anywhere along the route it could add to the heat.

Click to expand...

Did you test the fuel pump as described in the test path I posted?

If not , you have no way to be sure that the pump is working OK and there are no electrical problems.

A car that quits running and won't restart until it cools off needs a systematic diagnostic approach. When it quits running and won't start back up, do the checklist below.


Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995

A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work your way down. Jumping around will possibly cause you to miss just what you need to see to find and fix the problem. Don’t skip any steps because the next step depends on the last step working correctly.

Revised 26-Jul-2017 to add fuse link diagram.

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 to the Run position. 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, Crane, or other ignition box if present - Bypass it and return to stock configuration if possible. Do this as a temporary measure to eliminate it as a possible problem source.
B.) PIP sensor in distributor. The PIP sensor supplies the timing pulse to trigger the TFI and injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed. See paragraph 5A – Using a noid light will tell if the PIP is working by flashing when the engine is cranking.
C.) TFI module: use a test light to check the TFI module. Place one lead of the test light on the red/green wire on the ignition coil connector and the other lead on the dark green/yellow wire on the ignition coil connector. If the TFI is working properly, the test light will flash when the engine is cranked using the ignition switch.
D.) Coil
E.) No EEC or computer power - EEC or computer relay failure
86-93 models only: EEC 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.
Both 86-93 and 94-95 models: No 12 volts with the ignition switch in the run position on the fuel injector red wires. The relay has failed or there is no power coming from the ignition switch. Make sure that there is 12 volts on the red/green wire on the coil before replacing the relay.
F.) No EEC 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. Look for a 20 gauge blue fuse link connected to 2 black/orange 14 gauge wires.
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 on the ignition switch with it in the Run position. No 12 volts and the ignition switch is faulty. If 12 volts is present in the Run position at the ignition switch but not at the coil, then the fuse or fuse link is blown.
Note: fuses or fuse links blow for a reason. Don’t replace either a fuse or fuse link with one with a larger rating than stock. Doing so invites an electrical fire.
Ignition fuse links may be replaced with an inline fuse holder and 5 amp fuse for troubleshooting purposes.
94-95 models only: Check inside fuse panel for fuse #18 blown – 20 amp fuse
H.) 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.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness
I.) Computer. Don’t replace the computer just because you don’t understand how it works. Computers seldom fail, it usually is a sensor or wiring problem that causes the problems.
J.) 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.
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/blue 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.
See the Ignition switch wiring diagram for more information on the ignition wiring fuse link because it is the next thing to be tested. You will need a Multimeter or DVM and know how to use the Ohms function to check continuity between the red/green wire on the ignition coil and the red/green wire on the ignition switch. Make sure that the ignition switch is in the off position when you do the check. You should see less than 1 Ω (Ohm) between the red/green wire on the coil and the red/green wire on the ignition switch. More than 1 Ω means that the fuse link may have blown open and needs to be replaced. If you get 1 Ω or less means the fuse link is OK and the ignition switch is bad.

Wiring Diagrams:
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

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

AutoZone wiring diagrams: You can navigate to the diagrams yourself via Repair Info | AutoZone.com and select the car year, make, model and engine. That will enable you to bring up the wiring diagram for your particular car.

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: [/b]
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 2-4 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.) The PIP sensor in the distributor tells the computer when to fire the injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed.
A noid light available from any auto parts store, is one way to test the injector circuit to see if the injectors are firing. The noid light plugs into the fuel injector harness in place of any easily accessible injector. Plug it in and try to start the engine: it will flash if the injector is firing.
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.
B.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on.
C.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at the rear of the upper manifold).

See the graphic for the 10 pin connector circuit layout.

The injector power pin is the VPWR pin in the black 10 pin connector.

D.) No power and the 10 pin connections are good: look for broken wiring between the orange/black wire on the EEC relay and the red wire for the 10 pin connectors.
E.) 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-.1.0 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. If you removed the distributor, there is a good probability that you installed it 180 degrees out of time.
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.

@senorpavo
Electronic parts are the most common failure items in a situation that only happens when a car is driven for long periods of time and doesn't overheat, but does have problems dying or running poorly.

When fuel level in tank gets below the top of the fuel pump, temperature of the pump would rise if it were not for the "duckbill" on the end of the return line which sprays fuel on the pump to keep it cool.

A few hours of highway driving seems to indicate that this could be the issue.

The little orange thing with the clamp on the top of it at the end of the return line is the duckbill spray nozzle.
How many just throw this away not knowing it's function?

BTW, never use butt splice crimps to make the connections shown. Solder & heat shrink or heat shrink crimp terminals only.