What's a "power tester"? The definitive test is to view live data on a scanner. That will tell you in an instant if the sensor has 5.0 volts and ground, is generating a signal, and it's reaching the computer. You can view the waveform on an oscilloscope too. Being in tv repair for decades, I have many "scopes", but I never tried using one on a car. Some people try to use a digital voltmeter but those results are useless. Most digital meters don't respond nearly fast enough to such rapidly-changing signals, and there is no range that works for this type of signal. The voltmeter takes a voltage reading, analyzes it, then displays it while it takes the next reading. The waveform is a square wave pulse that is close to either 0.0 volts or 5.0 volts, like switching a light on and off. The voltage display on the DC range will be bouncing around and will be impossible to read. On the AC scale the meters are designed to measure a smoothly-changing sine wave at 60 hertz, not an intermittent square wave.
Some mechanics have digital meters that can measure the frequency of a square wave. That applies to mass air flow sensors on Fords where, as usual, they do things differently than everyone else, but that is a steady square wave. The signal from a crank or cam sensor is not steady. This varies from year to year and between engine sizes, but in general, once per crankshaft revolution, there will be a series of three square wave pulses coinciding with three holes on the flex plate, then nothing until the crank turns a quarter turn, then three more pulses, then nothing, then three pulses again, then nothing, then four pulses. The Engine Computer knows when number one cylinder is coming up to top dead center by the series of four pulses, only two pulses, or in some cases by the different sequence of pulses from the cam sensor. When you switched the engine, did you check if the flex plate had the same cutouts? If you reused the flex plate the truck came with, that is not an issue. If you used the flex plate that came with a different engine and the notches are different, the Engine Computer won't recognize them and it won't know when to fire the ignition coil. The firing order is not important to the computer when the engine uses a distributor to select the right spark plug to fire, but if the wrong series of pulses shows up from the crank sensor, the computer may not turn on the ASD relay, even though both sets of sensor signals are present.
Wednesday, January 22nd, 2014 AT 7:41 PM