Most people don't realize the ASD relay only turns on for one second. They think it should remain on all the time the ignition switch is on.
A '99 model is right in the middle of where they changed how the camshaft position sensor and crankshaft position sensor signals work. On older models, signals from both sensors are required for the engine to start and to run. Later, both signals were needed for the engine to start, but once running, it would continue to do so for that drive cycle if one sensor failed. Still later there was a backup strategy where the engine would start and run with a signal from just one of those sensors.
Neither sensor is involved with that first one-second burst from the ASD relay. That's controlled strictly by the Engine Computer. After that one second, it turns the relay back on when it sees engine rotation, (cranking or running). It knows that by the signal pulses from the two sensors.
I don't have an answer related to removing the battery cable. That's not a normal test procedure. I do know I usually hear multiple relays clicking when the battery is reconnected, but I wouldn't consider that a valid test. After that one second, there is probably a minimum amount of time that must pass before the computer will turn the relay on again for another one second.
Are you diagnosing a crank / no-start condition? If so, the fastest way to start this is to connect a test light to the wire that is the same color at any injector, ignition coil, or even either smaller terminal on the back of the alternator. Test lights work better than voltmeters because digital voltmeters usually don't respond fast enough, and you can set up test lights so you can see them from inside the vehicle. If it lights up for that one second when the ignition switch is turned to "run", we know that circuit is working and the computer has control of the relay. Next, watch if the light turns on steady and full brightness during cranking. If it does not, one of the sensor signals is missing.
One of the problems here is it is fairly common to not get a diagnostic fault code related to the missing signal, so don't assume the sensors are good. It can take some time, as when a stalling engine is coasting to a stop, for the computer to detect the missing signal. When there is no related fault code, you need to use a scanner to view the sensor status. I have a Chrysler DRB3 for all of my older vehicles. That one lists both sensors with a "No" or "Present". You're looking for one that doesn't switch to "Present" during cranking. Aftermarket scanners will have a similar means of displaying the status
You don't have to concern yourself with RPM. Whatever you read will be different between other models and years. Typically one signal is used for spark timing, and often the other signal is used for injector timing, and the computer may switch between them at different engine speeds to achieve more precise timing. This is where the unused signal may be switched in as a backup strategy on newer models when one sensor fails.
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Tuesday, December 31st, 2024 AT 12:41 PM
