Rev Counter Under Reading

[sk178ta]

My tacho. from working perfectly, has started under reading by about 50%. Coincidentally 2 days later I converted to Lumenition but it was doing it before. Speedograph have checked the tach. head, no problems. Any ideas?
Jim

[miked]

I had problems with mine reading low, not as much as yours. This just started and the error increased. I have always had a Aldon ignitor unit. I sent off my tacho to Speedy in south Wales. They fiited a new interior unit matched to the ignition. It now reads as accuarte as my mulitmeter test unit. It did come back as a voltage sensed unit as oppposed to an "in series" current sensed one. I think it was about ?80 with post and packing.


It is well known that the old RVI (i think) unit is not suitable for electronic ignition and tends to want to bouce anyway. So even if it were accuarte it has problems. There are articles about it on the net and I think on this site.

Purests like the old mechanism and dont like to tinker. I like to know were I am reving to!

regards Mike

[dmreeceuk]

I fitted an aldon ignitor and the tacho bounced like mad. I replaced the coil with a sport coil and renewed the ignition leads and its now rock solid and I noticed an increase in peformance an no more sooted plugs! I didnt convert my tacho.
I wonder if the problems with the electronic ignition is that the power of the signal to the coil is reduced (ie the current , assuming V stays the same: P=V*I) and the current sensing tacho struggled for a signal.
Aldon do recomend a sport coil for the ignitor.

I know its only the signal to the coil that goes through the tacho but perhaps the type of coil effects the signal.
<_<

Dave 1970 S4

[rickf]

I can't get my tach to work at all with Pertronix. Had it tested and there's nothing wrong with it. I'd welcome suggestions too.

[miked]

Me again! I have the Aldon flame thrower coil with my ignitor so I am matched up. Mine was acting up with the pair.
My friend has my old plus two and we found that the tacho tends to be stable when the plugs are new. As they age and build with carbon the tach bounces. This is why I went for the change of guts. To be fair the unit was designed around points.


regards Mike

[steveww]

I have the lumenition magnatronic system with a high output bosch coil fitted to my Elan. This system is very similar to the Aldon ignitor, the tacho is not totally acurate but not too far off given that it is 35 years old.

[the rolfie]

I have a plus 2 with standard set up but my tacho which was working for a short while has stopped working altogether, where does the signal come from the coil or the distributor? Also I have two wires that are not conected to the coil but are right next to it any ideas? Last question, my supressor is not conected at the moment to the coil as it doesn't have a long enough lead? All of the above are how I have found the car from the prevous owner?

[steveww]

I would guess that the set up is the same as the baby elan. Get yourself a copy of the workshop manual as it has wiring diagrams. However if your car's wiring is in the same state as mine when I received it the wiring diagram will not help - 30+ years of patches, jumps and hacks leaves you with a rats nest. I completely rewired my car last winter.

Anyway back to the point :rolleyes: The wire which should be white, goes from the ignition switch via the tacho to the coil. The coil is then connected to ground via points or electronic points. As the points open and close the coil draws current via the tacho in pulses and thus the tacho goes round. QED.

[dmreeceuk]

When I changed my coil I also changed my leads to carbon interference supression type so I could hear the radio - and cd . I wonder if it is the RF interference that screws up the Tacho.

Dave