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Engine cuts off then back on

Hyundai elantra 2003, engine will cut off when driving but will come back on. It is almost like turning a light switch on and off. It will run fine for days then it starts cutting off and on. When it is cold it seems worse. I have cleaned the battery terminals . It seemed fine for a few days then started again.

What else happens when the engine cuts off. Dash warning lights come on? Radio cuts off? Symptoms seem like an brief electrical failure, but where? Ignition switch maybe.

The check engine light is on due to code for catylitic converter needing attention. The headlights, dash illumination lights. radio all stay on. Rpm meter drops, engine check light itself goes out and in a few seconds everything back to normal running. Gets 30 mpg. Sometimes I can drive a hundred miles with no problem, then it starts doing it again. It acts just like flipping light switch on and off repeatedly.

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Could be mistaken for an engine miss. Check spark plugs cables for signs of insulation damage.Spray water on the cables while the engine is running,you might see sparks or arcing if you look carefully.Do this test at night because it is easier to see sparks.

That could mean that the crankshaft position sensor is failing intermittently.

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If the computer loses the signal from this sensor for even a second, the engine will cut off.

Tester

Failing fuel pump is another idea. My old VW Rabbit would sometimes quit running on the freeway. I’d pull over, wait 15 minutes, then it would start up and run as normal. That was caused it turned out by the fuel pump stopping b/c of a corroded/burned connection in the wiring from the pump to the fuel pump relay.

Check the alternator and make sure that the wiring it connected tight. Check the battery cables and make sure that they are tight and clean. Look for any loose ground wires to the chassis on the vehicle. If everything checks out to be working correctly, then the PCM may need to be replaced as it may have a battery disconnect condition. For further assistance or problem is unsolved go to a mechanic or a professional to have it diagnosed.