Starts but will not stay running

Is the security light flashing?

Not an ignition problem. The way the security system works, is it will allow the vehicle to start and run, then it cuts off power to the injectors. This is usually indicated with a start and run time of 2-5 seconds. This may, or may not be the case here. Any other information to help us diagnose? This site has some of the best Ford techs around, and I am sure one of them can easily help you further if I cannot.

Hi,

First, based on your description of the problem, I have to agree with the idea that it could be related to a security / immobilizer issue. However, if the security light isn't flashing, it is unlikely.

If you haven't already, I would start by checking for diagnostic trouble codes. Here is a quick video showing how it's done:

https://youtu.be/YV3TRZwer8k

I realize not everyone has a scanner, but most parts stores will lend or rent one to you. Give this a try first.

If there are no codes, what I suggest is to eliminate the possible caused. First, check fuel pump pressure to see if it is within the manufacturer's specs. It could have a weak pump.

Here is a link that shows in general how to check fuel pressure. Take a look through it first.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

In pic 1, I provided the manufacturer's specs for pressure.

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My next question is does the vehicle start again after it stalls and then just continue to do the same thing over? Have you checked if there is an issue with the crankshaft position sensor? This could also be related to that sensor. Take a look through these links:

https://www.2carpros.com/articles/how-a-crank-shaft-angle-sensor-works

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

If the vehicle doesn't restart, I need you to check for either an RPM signal to a scanner or if you have spark to the plugs.

Here is a link showing how to check for spark:

https://www.2carpros.com/articles/how-to-test-an-ignition-system

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If you determine the crankshaft position sensor is bad, here are the directions specific to your vehicle for replacement.

1998 Ford Mustang GT V8-4.6L SOHC VIN X
Procedures
Vehicle Powertrain Management Sensors and Switches - Powertrain Management Sensors and Switches - Computers and Control Systems Crankshaft Position Sensor Service and Repair Procedures
PROCEDURES

pic 2

REMOVAL

1. Disconnect battery ground cable.
2. Remove serpentine drive belt.
3. Raise vehicle on hoist.
4. Disconnect the engine control sensor wiring from the Crankshaft Position sensor (CKP sensor) and A/C compressor.
5. Discharge A/C system and remove A/C compressor.

pic 3

6. Remove retaining screw, then remove crankshaft position sensor.

INSTALLATION
1. Make sure the crankshaft position sensor mounting surface is clean and that the crankshaft position sensor O-ring is in proper location on crankshaft position sensor.
2. Position crankshaft position sensor and install retaining screw. Tighten to 8-12 Nm (71-106 lb-in).

CAUTION: Do not overtighten crankshaft position sensor retaining screw or damage to the sensor may occur.

3. Install A/C compressor. Evacuate and recharge A/C system.
4. Properly route engine control sensor wiring and connect electrical connectors to A/C compressor and crankshaft position sensor.
5. Lower vehicle.
6. Install serpentine drive belt.
7. Connect battery ground cable.

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Let me know if any of this helps. Also, if you have other questions or need help, let me know.

Take care,
Joe