speedometer is way off (almost double the speed)?

[mr2lickit]

OK I posted this in 240sx tech, but I never get replies there. SO I'm just going to link you there.

zerothread/197786

rundown: speedometer is showing about double the speed.

technical info: 97 240sx les14 transmission w/ j30 diffSE gauge clusterauto ecu and auto harness

[Q45tech]

Well as others have pointed out it could be speed sensor gear [wrong one] a KM vs MPH speedometer assembly oy just a defective failed speedo assembly.

One would start by reading the pulses from the speed sensor to determine the gear ratio.....correctness.

The frequency of the pulses is converted to a zero>5 volt to drive the speedometer [actually a 5 volt voltmeter].

[mr2lickit]

SO does the voltage read differently on the auto ecu vs. the manual ecu? IF so can you tell me the volt range on both of them? I really want to get this figured out. One last question, since the car is using a 97 auto ecu.....would a 97 manual speed sensor I guess send the correct voltage?

oh I lied I have a another question! WIll an auto speed sensor fit on a manual transmission?

[Q45tech]

The speed sensor is a frequency generator ..............voltage is a just a byproduct you must read the pulse frequency on oscilloscope / frequency counter. Sure it's not a head problem as little to go wrong in speed sensor if it works at all.