1999 Ford Cougar - Crank no start - Crankshaft position sensor diagnostic
This 2.5L V6 Ford Cougar suddenly decided to crank without starting... So I decided to make a video of the diagnostic process that lead me to a faulty crankshaft position sensor. Please note there were no DTC at all... In case of a no start condition, start with the basic stuff: an engine needs fuel, air, and spark to start. Here I am first checking the fuel pressure by priming the fuel system and pressing the fuel pressure relief port valve. As fuel is shouting out, the fuel pump can be considered as good. I am assuming air isn't the issue because the car has always worked fine before, it did not deteriorate over time but suddenly stopped starting. Spark is a bit more tricky to test and here I am only checking if the coil pack has power or not. One important thing that lead me to the sensor is the fact that the fuel pump would not engage when cranking at all. While it would engage for priming. So it sounds like the ECU is not even trying to power the pump. The most obvious reason for that would be a bad timing seen by the ECU which would then refuse to start the engine. An ohmmeter can be used to check the internal resistance of the sensors. It is possible to remove both camshaft and crankshaft position sensors from the car, but I decided to disconnect the main harness connector C3003 and test both sensors from there. The camshaft sensor reported an internal resistance of 350 ohms while the crankshaft sensor would act as an open circuit (infinite resistance). Having the C3003 connector disconnected, I decided to check for continuity from the C3003 connector to the sensor connector (maybe the harness is bad, not the sensor?). Results were what I expected: harness is good, sensor is dead. Replacing the crankshaft sensor solved the problem. Both camshaft and crankshaft sensors are bolted to the engine with one 8mm bolt each. Do not overtorque these bolts! NOT COVERED IN THIS VIDEO: If you have access to an oscilloscope you can also monitor the sensors outputs. On this car the camshaft sensor would output a nice sinusoidal signal when triggered. The crankshaft sensor however when measured at the C3003 connector would only pick 50hz noise from the high tension power lines nearby, the harness acting as an antenna. That also tells me there is no short at the harness between the two sensor wires as this would make a flat grounded signal on the scope.
This 2.5L V6 Ford Cougar suddenly decided to crank without starting... So I decided to make a video of the diagnostic process that lead me to a faulty crankshaft position sensor. Please note there were no DTC at all... In case of a no start condition, start with the basic stuff: an engine needs fuel, air, and spark to start. Here I am first checking the fuel pressure by priming the fuel system and pressing the fuel pressure relief port valve. As fuel is shouting out, the fuel pump can be considered as good. I am assuming air isn't the issue because the car has always worked fine before, it did not deteriorate over time but suddenly stopped starting. Spark is a bit more tricky to test and here I am only checking if the coil pack has power or not. One important thing that lead me to the sensor is the fact that the fuel pump would not engage when cranking at all. While it would engage for priming. So it sounds like the ECU is not even trying to power the pump. The most obvious reason for that would be a bad timing seen by the ECU which would then refuse to start the engine. An ohmmeter can be used to check the internal resistance of the sensors. It is possible to remove both camshaft and crankshaft position sensors from the car, but I decided to disconnect the main harness connector C3003 and test both sensors from there. The camshaft sensor reported an internal resistance of 350 ohms while the crankshaft sensor would act as an open circuit (infinite resistance). Having the C3003 connector disconnected, I decided to check for continuity from the C3003 connector to the sensor connector (maybe the harness is bad, not the sensor?). Results were what I expected: harness is good, sensor is dead. Replacing the crankshaft sensor solved the problem. Both camshaft and crankshaft sensors are bolted to the engine with one 8mm bolt each. Do not overtorque these bolts! NOT COVERED IN THIS VIDEO: If you have access to an oscilloscope you can also monitor the sensors outputs. On this car the camshaft sensor would output a nice sinusoidal signal when triggered. The crankshaft sensor however when measured at the C3003 connector would only pick 50hz noise from the high tension power lines nearby, the harness acting as an antenna. That also tells me there is no short at the harness between the two sensor wires as this would make a flat grounded signal on the scope.