Lotus Elan and Lotus Elan Plus 2 Forums

Well, I found the connection I hadn't made...connected it to the positive terminal of the new coil...blow me...now the tacho is reading approx double...now what?

Hi

the tacho can sometimes play up if different style coils are in use. (coils with lower resistance for bigger sparks for example). I assume you have standard ignition set up with points and that the tacho is a Smiths RV1 type with a pick up loop for triggering it. The usual wiring for this is the lead from the switched ignition (either picked up from the ignition switch or the voltage regulator if U have a dynamo) goes through the tacho pick up loop and then to the coil +ve or SW terminal. Depending upon car build and age the wire colour may be white, white yellow, or red green. It may be that the current from the ignition to the coil goes through the tacho the wrong way round, or as can sometimes happen a takeoff of some accessory from the coil +ve or SW terminal is putting some other extra current through the tacho loop.

hope this helps

best of luck

bob

http://www.flickr.com/photos/16638375@N ... 680361796/
Neil

It gets even more bizarre!

Just had a little drive....

Tacho kinda reads double...until I brake...then nothing at all...indicators send the needle nuts...and the electric windows kill it too!

Electronic ignition/RVI tacho!

I was getting intermittent gauge failure (tach and fuel gauge went to zero when I turned on the indicators) until someone mentioned cleaning the fuses. Cured it!

Hi

the problems with funny behavior when other gadgets are switched on does suggest iffy wiring like the other posts suggest. But some electronic ignition systems do not work well with the Smiths RV1 style tacho. Do a search on the web for the type of ignition you have you have and see what they say. Some (I believe the Aldon Ignitor but not 100% sure so check this), claim the tacho will not work at all with their systems

best of luck

Bob

jonnyconcrete wrote:It gets even more bizarre!

Just had a little drive....

Tacho kinda reads double...until I brake...then nothing at all...indicators send the needle nuts...and the electric windows kill it too!

Electronic ignition/RVI tacho!

My H&H system had no adverse affect on the RVI tacho.

When strange electrical things happen on Elans it nornally relates to iffy earth connections somewhere.

voltage stabilizer..?

No cct drg in front of me but worth a check, is the fuel gauge acting up too?

cheers

Mark

As recently mentioned the rev tacho is NOT to be fed its power through the voltage stabalizer; that is is crude on off vibrator thing and will play hell with the action of a tacho.

Your tach may be too sensitive with your new coil. If you have a loop the loop (as in the above diagram), just try a straight pass through of the ignition coil wire (white) through the sensing loop. Also clean the contacts of the removable half-loop (springy U shaped thing) and gently squeeze the ends of the half-loop to ensure good contact with its other half.

hi again

The full part number on my tacho is RV1/2434/00. I have tested this unit and its calibration is reasonably stable with a battery supply in the range 12 to 15.5V. Thus it does not need to be fed from a voltage regulator as such. If there is any noise on the power line ( and/or earth return ) or if the ignition coil produces a pulse in the power feedlines due to iffy current paths from coil to engine it can behave very erratically.
some electronic ignitions remove the (equivalent of) points capacitor. This can make for a noisier voltage pulse on the primary of the coil and may contribute to the problem.

hope this helps

Best of Luck

Bob

Mine is RVI 2402/00B

If the electronic ignition is not the cause, then the internal capacitors in the tacho could be low value, and allowing extra pulses through.

If you can go back to points and the tacho is still playing up, and you feel confident, follow the procedure below from one of my old posts (otherwise use someone like speedycables.co.uk to fix the tacho):

1. Remove rev counter, and carefully turn the bezel until the tags line up with the slots in the case. The bezel may well be gunged up with a black pitch-like substance, which hopefully has turned brittle and does not give too much trouble.

2. Two screws at the rear to undo - be ready to catch the inner assembly in your hand as it makes a break for freedom. Have clean hands and be careful not to damage that pointer, and the thin winding wire now exposed.

3. Take a look at the vintage printed circuit now on view, You should see a black component with 2uF 16V written on it, and a + sign. This is an input decoupling capacitor which is supposed to filter out the high frequences in the current pulses. It is this component that loses capacitance over time, leading to erroneous readings.

4. Find a replacement electrolytic capacitor - I used a 2.2uF 35 V item - make sure the value is 2.2uF, and the voltage rating 16V or more.
Maplins or Tandy should have one.

5. If your original capacitor is a different uF value, go for the closest match you can - it should work.

6. Replace the capacitor, making sure the + terminal of the new component goes the same way round as the old component. You will need basic soldering iron skills - and a soldering iron (or know someone else with one).

7. At this point, if you have a multimeter, it is worth checking the resistors in the circuit as well. Change them if they have drifted in value more than 15% or so. If you don't have one - don't worry, just re-assemble the rev counter and give it a whirl...

Dave Chapman.

OK...Just replaced the lead to the tacho, with a 75 ohm coax. At 900rpm, according to my multi meter, using coax flown around the outside of the car tacho is rock solid at 1200rpm. Back to the cable and the needle wings around +- 300 rpm about 2000rpm.

Using the coax, as soon as another electrical appliance is used needle drops to zero and stays there until other feeds are turned off. With the lead, kind of the same...except the indicators make the needle act like a windscreen wiper!!

Thoughts.

Stuart

Hi All

If you go the the (rather long!) link below there are a few review pages about classic car electrics book.
on the pages displayed there is a circuit and a description of the RV1 type tacho.

Could prove helpful

Bob


http://books.google.co.uk/books?id=9kQ9 ... &q&f=false

Coax does not sound like the right kind of wire for this job at all.