Ive got a 2005 Ford Mustang V6 automatic with an unknown problem. I had to replace the thermostat casing because it got a leak and also replaced the thermostat whle we were at it. A few weeks later the car was making a loud screech and we found out the water pump was bad and replaced it along with getting a new serpentine belt. A few hours after replacing the water pump the car engin just shut off but i was still in control and able to maneuver the car. After the engine shut off we were able to turn the car on but every 5-15 minutes the engine would once again die even when it was sitting idle. The Car never completely lost power as the alternator and batter both still worked because the radio was playing, but the engine did. We tested the battery, the fuel line, the spark plugs, fuzes and the mechanic ran the test and no error codes came up. The engine was running perfectly smooth but still randomly just shuts off. Their is an after market alarm on the car which was put on before i purchased it. Hoping some of you car experts have some advice as to what may cause this.

 

Disconnect the alarm. There is some type of killswitch that's part of the alarm system- commonly an ignition interrupt- that is causing the issue.

Never use an alarm company that can install a system within a few hours. All they do is take a generic module and use splice connectors (self-cutting type) which eventually will fail. I recommend using a factory alarm that any dealership can activate; unless you have a buddy with wiring tools and an IDS.