Tach problem

[zeca]

Hi,

I rewired my Elan S4 and I?m having problems with the tach. With the engine running, I wire the tach and then the engine stops... (the tach moves in that short period).

any help?


kind regards

[Grizzly]

Have you fitted Electronic Ignition to it? and do you have a good ground to the Tach?

[zeca]

original ignition... ground ok!

[prezoom]

A good place to start would be reviewing the article in tach wiring in Moss Motors MGB catalog. Covers changing from positive earth to negative within the tach and the reversal of the loop wire through the connector on the back of the tach.

[Chancer]

Sounds like the loop connection has become grounded.

[pharriso]

Sounds like the loop connection has become grounded.

That's what I was thinking...

[Grizzly]

Just slightly off topic but is there an Electric Ignition that will work with the stock Rev counter??

[billwill]

Just slightly off topic but is there an Electric Ignition that will work with the stock Rev counter??

The very simple Electronic ignition, which is merely a transistor amplifier (Velleman kit from Maplins) seems to work OK with a standard tacho. I made one up for my car but replaced the underrated resistor(s) that feed the distributor contact breaker, with a much higher rated (10 watt ) resistor so that it will not burn out if the engine stops with the contacts closed.

http://www.velleman.co.uk/contents/en-u ... otive.html

http://www.velleman.eu/downloads/0/illu ... _k2543.pdf

This kit is very simple and merely serves to reduce the current through the contact breaker and move the capacitor elsewhere (to the output of the circuit), so that the contact breaker does not arc accross. This reduces the wear on the contact breaker to near nill and they last much longer.


NB: Looking at that PDF file they seem to have adjusted the values and ratings of R1 & R2 now to further reduce the current compared to what I had before and at first glace it looks as if it is now safe in a stalled engine.

Circuit now has two 330 ohm resistor in parallel, i.e 165 ohms.
so current at 12 volts = 12/165 = 0.073 amps
so power dissipation in the resistors = 12*0.073 = 0.87 watts
Since there are two resistors each rated at 1 watt, that looks plenty safe with over 100% safety factor

[Geoffers71]

I have an Accuspark Electronic Ignition with a standard Tach, BUT you do have to adjust the tach to read correctly, which is not difficult. See my project thread

[rgh0]

If the standard tach is in good condition and if you don't introduce extraneous current pulses into the ignition to coil wire that goes through the tach current sensing loop then the standard tach will work.

I know it works with the optical lumenition electronic ignition for example.

The most common problem is people power the electronic ignition system from the positive terminal of the coil as it is close by and convenient and is what is shown in most of the wiring diagrams that come with the units. This unfortunately introduces additional current pulses into the power supply to the coil as you now have the normal current pulse when the coil is charging that the tach is designed to detect and also a current pulse when the electronics are switching and the tach can detect both depending on their size and shape and the condition of the tach electronics thus giving false readings

Some electronic systems may also change the shape and size of the current pulse to the coil and this may affect the tach depending on its state also even if the ignition electronics are powered from a different source and not the coil positive terminal.

cheers
Rohan

[ericbushby]

Just slightly off topic but is there an Electric Ignition that will work with the stock Rev counter??

I bought an Ultraspark unit from Ignition Car Parts and it worked correctly straight away.
It is a Hall effect type and fits inside the distributor with one screw to replace the points.
The part no was ICP EKO 18 I think but the on line catalogue should confirm that. I fitted that 3 years ago and have not looked at it since.
Negative earth only.
I even got away with feeding the 12volts to the unit from the coil supply with no trouble.
Eric in Burnley
S3SE DHC

[zeca]

i don?t have electronic ignition....

[Grizzly]

Did you check the loop connection isn't damaged or grounded? Pull the tach out and connect the Ignition-Tach (Usually white and a bullet connector) and the Coil trigger wire (Again usually white and a bullet connector) together to bypass the Rev counter if it stops cutting out etc buy one of these kits and fit

https://www.spiyda.com/magento/index.ph ... board.html