tachometer not accurate
- Thread starter Rick
- Start date
- Status
rick
First, before buying a new tach, etc., find the tach "sender" on the flywheel (follow the wire from the tach to find it). Make sure the nut is tightened down well at the sender. It's probably loose. I had the same problem, and that was what was causing the faulty tach readings.
First, before buying a new tach, etc., find the tach "sender" on the flywheel (follow the wire from the tach to find it). Make sure the nut is tightened down well at the sender. It's probably loose. I had the same problem, and that was what was causing the faulty tach readings.
Alcernator problems
While you might have a tach sender like Buch indicated you alternatively have a tach that reads the alternator stator signal. The AC voltage frequency in the alternator stator (the outer windings) is directly proportional to the engine speed and so you can make a cheap frequency meter and calibrate it to read RPMs. If the tach wire runs to the alternator you may still only have a connection problem or you may have an alternator problem. Have you done anything to the alternator recently. Like put on a new regulator. Some regulators don't play well with tach gages as they turn the alternator rotor current off and on rapidly instead of just changing the rotor voltage. This totally eliminates the alternators output and screws up the frequency the tach sees. The alternator works fine but the output is not one the tach can use.
While you might have a tach sender like Buch indicated you alternatively have a tach that reads the alternator stator signal. The AC voltage frequency in the alternator stator (the outer windings) is directly proportional to the engine speed and so you can make a cheap frequency meter and calibrate it to read RPMs. If the tach wire runs to the alternator you may still only have a connection problem or you may have an alternator problem. Have you done anything to the alternator recently. Like put on a new regulator. Some regulators don't play well with tach gages as they turn the alternator rotor current off and on rapidly instead of just changing the rotor voltage. This totally eliminates the alternators output and screws up the frequency the tach sees. The alternator works fine but the output is not one the tach can use.
A good tach tach will either read or not
depending on the sensor and connectors. When the indicator starts hanging up like that and behaving erratically the unit is usually shot. The following diagnostic routine is good for Yanmar engines. Locate the sensor in the top of the flywheel housing. To test the sensor remove clean and retighten. Disconnect the leads and with the engine stopped check the resistance between the terminals. Resistance should be between 1500-1700 ohms. Now run the engine and measure voltage between the terminals. The voltage reading should be at least 1 volt. If the sensor fails either test replace sensor. To check the tach disconnect the red/black and black wire from the unit and with the key on, measure the voltage between the wires. It should be 10-16 Volts (battery voltage) if not determine why (wiring and connectors for electrical circuit). Disconnect the orange and blue /red leads from the tach. Run the engine and measure voltage between the leads. It should be at least 1 volt. If reading is less than one volt check connections and test sender if it has not already been done. If all voltage readings are satisfactory the tachometer unit is bad and needs to be replaced. Good luck
depending on the sensor and connectors. When the indicator starts hanging up like that and behaving erratically the unit is usually shot. The following diagnostic routine is good for Yanmar engines. Locate the sensor in the top of the flywheel housing. To test the sensor remove clean and retighten. Disconnect the leads and with the engine stopped check the resistance between the terminals. Resistance should be between 1500-1700 ohms. Now run the engine and measure voltage between the terminals. The voltage reading should be at least 1 volt. If the sensor fails either test replace sensor. To check the tach disconnect the red/black and black wire from the unit and with the key on, measure the voltage between the wires. It should be 10-16 Volts (battery voltage) if not determine why (wiring and connectors for electrical circuit). Disconnect the orange and blue /red leads from the tach. Run the engine and measure voltage between the leads. It should be at least 1 volt. If reading is less than one volt check connections and test sender if it has not already been done. If all voltage readings are satisfactory the tachometer unit is bad and needs to be replaced. Good luck
- Status