rev counter going up and down while idling

Mar 14, 2005 3 Replies

Hi



While stood in traffic the other day the rev counter starting going up and down, maybe to about 4000rpm although the engine didnt seem too for about



5-10 sec, it looked although i cant be sure that the needle went back down quicker than if done by gravity, so in effect pulled back down, next minute it cut out, but a quick turn of the key got it going fine, a mile later it conked on a round about, pulled off. and took some doing to get it going, been fine since.

Does that sound like a bad earth, coil failing, although i have known coils work or not suddenly, never pre warn by playing up.



mid 70's car so no fangled electric stuff. The wiring is a mess from the previous owner so a lot of stuff doesnt match the manual.



ta


Your fault is in the switched LT side of the coil, which on basic engine electrics such as yours (presumably) consists of the coil, contact breaker and the wire between!

Contact breakers are the cheapest to replace, easy to check visually (maybe a weak spring?) and are a replaceable service item. If that doesn't work then like you said, try a new coil.

Darren

thanks, there is a ballast resistor which has a lump of porclain missing, its the wire that keeps the currant going once it has fired up, i remove that as a anit theft device. It doesnt look too stable.

I have a spare coil carried in the car that i removed from a year later model, diff engine but i swopped over some time ago.

Surely the ballast resistor fits in the positive (i.e. unswitched, though it is actually switched with the ignition) side of the circuit? If so then this should have no effect on the tacho readings as that (should) have it's own supply + and - as well as the pulsed input from the contacts...

Darren

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