Xj4.0 1990 sallon

XJ40
1

engine trouble tachometer fail,what problem? many thanks

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2

Usually this fault is caused by a failing Crankshaft Position Sensor, depending on Vin #, either part number DBC2139 or from Vin 629286 DBC11501

(edit) I’m guessing the engine doesn’t start?

If the engine runs it would be something else!

good luck

Larry

3

is the engine runs fine, thank you

4

The tachometer is driven directly from the Ignition Amplifier via the negative terminal on the Ignition Coil through a 6.8K Ohm resistor. If the engine is running fine then the Ignition Amplifier and the Coil must be OK.
Consequently the fault must be ‘downstream’ of the Coil - either a connector problem, or the resistor has blown or the tachometer instrument itself may have failed (although that would be the first instance of that I can remember)

Check the White/brown wire from the negative terminal of the coil to that resistor and then the Red/yellow wire from the resistor through its various connectors to the instrument pack itself.

The connectors through which that Red/yellow wire passes are:-

9-way Yellow connector in Engine bay above Coil
24-way Yellow connector on right side ‘A’ post under dash
24-way Black connector behind instrument pack.

BTW, if the engine is running in your photograph, I see that you have a blown bulb somewhere and an ABS fault.

5

many thanks bryan for xj4.0

6

Hi Bryan,

i have the same problem.
where is the resitor located on a lhd 3.2 'my92?

thanks

ps, how many watt should a new resitor be

7

thanks,
this explination helped me. tach works again. there was a wiring problem between the coil and the yellow connector abvove the coil; replaced it with a new wire and a resistor