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hello there...I have a very strange and bizarre situation.....I have a 1998 mitsubishi galant (GDI) which had a head job done.....since then i could not start ....I diagnose the problem myself and found that on a few sensors the signal wire was shorted to ground when the sensors was plugged in....these are the cam and crank sensors.. when i unplugged the sensors they all had the correct voltage....12 volts power....5 volts signal and good ground...However when i plugged them in the signal wire drooped to about .25 volts ...So i thought it was the sensors I replaced the cam with a new one only to have the same thing happen...It reads good unplugged but ground when plugged in.....I know its not the computer because it reads good unplugged also the harness and the computer were changed....I am at a loss to what could cause this..any help would be greatly appreciated
I believe you need to check the signal wire with a scope and not a DMM when the sensor is plugged in while cranking or the engine running. It is most likely a digital signal (ie - either 0 volts or 5 volts) and depending on the duty cycle, the DMM is only taking an average reading.
With a scope, you can compare the actual waveform to a known good waveform to determine if the sensor is good.
With the sensor unplugged the 5v you have on the signal wire is proberly a bias voltage.
The signal wire when plugged in would have a small amount of voltage, proberly the .25v you say you have which is pulled up when activated. If this is digital this will create a 5v on/off square wave which you couldn't see accurately on a volt meter.You would see the average would could be anywhere from .5v upwards to near 2.5v for a 50% duty cycle. You will need a scope to see this.
Now someone point out if I'm wrong here... but if you have a test light on battery positive and you quickly touch the signal wire on n off repeatedly you should see a reaction on live data where you are pulling the signal up creating an input..
If you say you think you have shorted signal wires on multiple sensors... These signal wires are not shared. You could have a shorted 12v if you were loosing these on multiple sensors..
If you find you have a square wave at the sensor your need to check the same wire at the pcm. If you have no signal and the power n ground are ok you need a sensor
Live scope data is what you need
