SiBorg
12.06.2021 12:59:15
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See full version: How to Check a Tachometer
This article has been viewed 6,660 times. [links]
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If you've noticed that something seems off with the gauges on your car, motorcycle, or boat recently, you might be wondering if something is wrong. A simple way to start troubleshooting is by checking the tachometer, which measures how fast the engine is spinning in revolutions per minute (RPM). This number has typically been shown with an analog dial, but newer displays are digital. Cars, motorcycles, and boats all have tachometers. They function and can be read in the same way, and you can even use similar methods to troubleshoot and fix tachometers, no matter what type of engine you have. You might have lots of questions about checking this instrument if it's your first time. Don't worry, we've got you covered! Keep reading for answers to your common questions.
This car has had the 2.2 ltr modification, has Pertronics ignition and appears to have no ballast resistor.
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Also my PO included with the car 2 additional JH tachometers with tags 164 and 424. These numbers do not match nor do they match one installed in the panel. Curiosity compels me to ask if anyone knows the significance of the numbered tags.
I don't know whether the male pin on the tach goes to the +12 volts or to the ballast, you'd have to check your wiring harness. here
The green wire is the power supply for the tach. This should be +12 volts when the ignition switch is ON. The black wire connects to the body of the tach, and goes to chassis ground. more
For the panel wiring harness, 54960862D is the Lucas drawing number. The Jensen part number would have been 90843. Not certain what the 2205 is, perhaps it's a date code of some sort. The 32 in a U sounds like an inspector's approval stamp.
Basically i found my issue inside the dash. It was a faulty resistor on the pcb, that didnt allow the input voltage from the coil to arrive at the IC chip which converts that varying volatage into an RPM reading. It was alot of mucking around, but in the end worth it, My RPM guage to me is more important then my speedo as i use boat for watersport, so RPM gives me a more steady/reliable reference.
The tachometer signal is not a DC voltage that varies with engine speed. [links]
The tachometer signal is a pulse whose frequency varies with engine speed. The voltage range of the pulses is really rather constant. The negative peak of the pulse is near 0-Volts DC or slightly below; the positive peak is close to the battery voltage. Since the battery voltage rises slightly with engine speed due to charging current, the tachometer pulse peak positive voltage will rise slightly, too. But this voltage change is not what is measured by the tachometer. [links]
Having a faulty tachometer in your car can be very dangerous. You could end up without your driver’s license and not be able to go to work if you have no other means of going than by your car.
Once you have located the ground wire, it will lead you to the breaker box. When you have located the box, locate the wire that leads to the tachometer. [links]
Here’s the deal: You need to open the hood of the car and locate the ground wire. Ground wire is usually visible on a thin part that leads from one side of the car to another, located between the engine and the body of the car. [links]