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More Tacho problems

Richard Anderson

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I've just had a new model Caterham tacho (0-8K) installed becuase the old one was waving about badly and although the new one is a definate improvement it :-


1) Still waves around a bit

2) doesn't seem to be calibrated properly....either that or my SLR now revs to 9K+! :-o

3) as soon as the revs approach anything near 6K+, just jumps to max


Will twisting the tacho so that max revs are at 12o'clock help to check it's over-exuberance (ie has to work harder against gravity)?


I have a MBE ecu....what do I check to make sure it is generating the pulses correctly?

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The only real way of ascertaining whether the tacho, or the signal to the tacho, is at fault is to connect an oscilloscope to the black/white wire on the back of the tacho. There should be good square wave pulses of 6v amplitude running at twice the engine revs (due to the wasted spark system). If the pulses look good throughout the rev range then the tacho has a problem and vice versa if they don't. As you have changed the tacho and that didn't cure the problem, I suspect the pulses are dicky.


Worth checking too that you have good solid connections to the back of the tacho. The relevant wires are:

green = +12v (with ign ON), black = ground, black/white = input pulses from ECU pin 55 (small ECU connector)


I appreciate that finding an oscilloscope is not easy - I have one but have no idea of your location. I am located near Dunstable in Bedfordshire.




1.8K SV 140hp see it here

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