Quote:
Originally Posted by benzwagon440
Hi all,
trying to get my tach working again. I know it's not vital but I'd really like to have it working ...
Am I missing something? Anyone have a similar experience?
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The system is pretty simple really. Here are the components
[1] Variable Reluctor sensor (82) - On the transmission (reads flywheel teeth)
[2] EGR Computer (80) - processes signal
[3] Tach (a) - signal to gauge
[4] OVP (85) = provides power to controller
You can't really test the VR sensor without a scope as it puts out A/C current. But these are generally bullet-proof - the least likely suspect. Just check for good wiring and make sure the sensor is solidly in place. (Actually there is a way to test the VR sensor - see below for a simple VR tester setup)
You can look for 12v on pin 1 to verify the OVP (or take power from an unconditioned source for testing).
You could pull a tach unit from the JY to test the actual gauge (or pull the unit and test it in a known good vehicle, if you have a friend with one) If those all test good, you're most likely point of failure is the controller.
Because of the corrosion you report on the contacts, I'd probably bet on that being the problem.
VR Tester
When I was working on my mechanical to electronic speedometer conversion I rigged up a VR tester, like this
It was just a convenient hole saw with a number of nuts taped to the circumference. (I used 4 for the speedometer because there are 4 teeth in the trigger wheel at the rear of the transmission) Nuts aren't the best because they have a hole in it that could create the appearance to the system of two teeth. In your case I'd suggest using something solid with as many "teeth" as possible for the trigger wheel and about 1/2" high (the one on the flywheel - flywheel starter ring teeth actually) has around 50. Then to test, take the VR sensor out of the intermediate plate and hold it close to the make-shift trigger wheel "teeth" and watch the tach. You should see a smooth rise as you increase the speed on the drill (assuming everything else is functional).