Tachometer trouble

[aero]

Since fitting new plugs, leads, distributor, rotor arm and coil the tachometer has started to flicker and now reads about 500 rpm higher on tickover.
I have checked the wiring and made sure the low voltage side of the coil is well away from the high and even added some tin foil rap to the low voltage wiring in this area, but the problem remains.
Does anyone have an idea what could be causing the problem?

Thanks

[CaptiV8ed]

There's been lots of talk of this happening with Magnecors. If you've fitted them, then maybe...

[aero]

yes, I fitted Magnecor leads !

[serious pete]

I have had the same problem in the past and i have cured it a couple of times,

try a longer king lead, doesn't really cure the problem, but seems to hide it.

I have also reversed my original opinion that the Magnecors were causing the Problem, I have a full set of standard brand new Land Rover and they did not solve the problem, I think the new leads are just highlighting an existing problem.

Possible casues i think you may want to investigate

1 Arcing under the bonnet
2 Faulty dizzy cap, particualry the cheap blue ones
3 Dodgy Alternator- try disconnecting the Alternator belt and starting the engine briefly to see if that fixes the problem, don't run for any length of time though.
4 Ignition amplifier playing up
5 Dodgy Earth somewhere,
6 Dodgy Coil
7 or the tacho itself could be faulty.
8 loose nipple things on the end of the spark plugs

good luck

[spend]

So you've narrowed it down to just about anything eh

You've not been experimenting with that funny 'W' terminal on the alt have you (its for LR tach only IIRC)

Dave

[aero]

I phoned ACT where I purchased the leads and they said it was not common but it could be the leads.... trouble shooting so far tonight !

Made sure there was good segregation/between HT and LT sides of the coil.
Back the old coil .... no improvement.
Back to the old leads.... no improvement.
Bach to the old rotor arm and distributor .... no improvement.

I will try some more of your trouble shooting advice later !

Thanks for the help

[Nick P]

I have Magnecors and the problems comes and goes.....it also varies with the routing of them.

[serious pete]

try fitting the King Lead loosely, this will increase the resisitance.

If that fixes the problem (as it did on mine) I think the problem is that the tacho is getting a noisy signal. There was a great post by a clever person on a related thread which explained this very well, but can't remember where i saw it.

The noise be caused by all kinds of stuff but old wiring or the ignition amp are favourite. I've got a replacement amp on order so i'll post what happens when i fit it.

[miketvr]

Had this problem recently and changing the leads solved the problem. Bosch leads from memory.

Check the routing of the leads are not close to other low voltage wiring.

Mike

[serious pete]

Tried the new ignition amp,didn't make any difference also tried

coil x 2 (both known good ones)
dizzy cap x 3
Rotor arm x2 and (Brand New)
Brand new Lead set (Land Rover)
disconnecting Alternator Drive Belt.
Also Super Super carfeully routed Leads

The only thing that worked was a loosely fitted replacement King Lead, The engine is running as it always has so i think that the problem has to be the tacho itself just picking up the noise from an otherwise (dizzy) excepted brand new ignition system. or a tacho related wiring issue

Replacement Tacho here i come, If Aero hadn't posted this problem I would probably have just lived with it, but i got all buzzed up, and now i still have the problem and less money.


Does anybody has any other suggestions?

[aero]

I have now tested everything proposed and still have not found the cause of the problem either..
My next stop is the wiring to the tacho, does anyone know if this come directly from the coil or from the amplifier circuit ?

[davetherave1970]

Just to add to the confusion......Not my tacho but my speedo. Mine used to bounce while the car was at a stand still. It read between 0 and 130 but only sometimes.
Had a problem with the cooling fan relay. Changed it and it's stopped the speedo problem

Maybe a relay is on it's way out and feeding back to cause your tacho problems!

Just a thought.

Edited by davetherave1970 on Wednesday 25th April 22:27

[spend]

aero said:

I have now tested everything proposed and still have not found the cause of the problem either..
My next stop is the wiring to the tacho, does anyone know if this come directly from the coil or from the amplifier circuit ?

Mine goes directly to the low tension side of the coil via a couple of connectors in the dash.

Dave

[john p]

Make sure the leads,especially the one to the coil are not touching the pipe to the coolant tank,if this happens on mine it causes problems with tacho.

[ozstyle]

Hi,

I recently changed my HT leads and picked up a dancing tacho needle. After reading a few threads I swapped the king lead back to the one I had removed and all steady again. Both leads were the same length and routed exactly the same. Very strange, obviously something to do with the physical properties of the leads.

[aero]

A week of trouble shooting and I still have not identified the exact cause..
Through carefully laying out the leads and HT/LT separation checking and replacing and re-checking everything that was changed the dancing has calmed down to a small erratic twitching.
I have found some EMI tape on the WEB that I will apply to the LT lead and tacho wiring later, but I guess It will become one of those mysteries of the car.

Thanks for all the help.

[serious pete]

aero,

Let me know how the EMI tape works, I have gone the whole way and ordered a new Tacho form Greengauges.com and a matching speedo that can be calibrated properly, my current speedo is from the choclate teapoot school of usefullnes.

[spend]

serious pete said:

aero,

Let me know how the EMI tape works, I have gone the whole way and ordered a new Tacho form Greengauges.com and a matching speedo that can be calibrated properly, my current speedo is from the choclate teapoot school of usefullnes.

Do CAI make a speedo the same size - I thought they were a tad different, with a 93 car the recess is hard to match. ETB (I am assuming you have ETB clocks) have given PH'ers pretty good service on the past - and the speedo is adjustable as standard. The early speedo/sender combination generally seems to have caused less problems than the later variants (maybe just pre T5 box) judging by the comparative 'noise' on these forums.

Dave

[serious pete]

I am fairly sure the CAI gauge will fit (fingers crossed), I have used their stuff before and have been very happy with it

Also i am very keen to get rid of the 1/10th mile click and add a trip meter and the cost of doing this was about the same as a new speedo anyway.

[serious pete]

Whopee

Fixed it again, Gauges arrived late this afternoon and as i was "working" from home finished a bit early and put them in.

I now have a Tacho which tells the actual engine speed and a Speedo with a digital odo and trip, the Speedo can be calibrated by a remote switch and both the tacho and speedo light up the same brightness and no 1/10 mile ticks

Fitting was easy apart from getting the B****** dash top off

i also found out the coil + - were on the wrong way round, don't think this should make much difference car seems to run the same this way round.

Heres what they look like

http://good-times.webshots.com/photo/