Rev Counter

[r0lex]

Can anyone throw light on to this, for some reason my rev counter will drop to zero and after a few seconds work correctly again. I have just checked for loose wires but there does not seem to be any. Car runs fine just the rev counter hates me :}

Thanks
Paul

[SimonP]

Paul,
Is this a new build, or something that's been running OK for a while and now it's not?

Please post info on make/model of tach and type of ignition - points, electronic, MSD etc.
Also whether loss of indication is random, or at certain rpm, or under acceleration/deceleration etc.

Simon.

[r0lex]

thanks for your swift reply, this is not a new build it is a sumo mark 2 with rover 4.6 i will have to go up the garage to get the make of the clock but what i know at the moment is,
loss of indication is random
i notice it more at about 1500 rpm and under then it just drops then comes back again.
under light acceleration
distributor is Lucas 'Limb' system 35DLM8

Thanks
Paul

[SimonP]

Paul,
I'm guessing this is a "voltage operated" tach. If it was a "current operated" tach, loose wiring connections would affect the power supply to the ignition and cause a misfire.


Do you have access to a multimeter?

If you have, try these tests:

1. Power to tach: Connect multimeter on volts DC between tach + supply and tach earth.
Have an assistant watch the meter as you go for a drive. See whether the supply is lost when the indication is lost.

2. RPM signal from ignition: Connect multimeter on volts AC between the tach input and tach earth.
Have an assistant watch the meter as you go for a drive. See whether the voltage is lost when the indication is lost.

The usual culprit on tach failures (if it's definitely nothing external) is a capacitor either failing or becoming dry-jointed on the circuit board inside the tach.

Simon.

[r0lex]

i just love this web site it is full of information, i will try that tommorow simon,

thanks :tu

paul