Autosport Labs

Hello all

I have a 1600cc Fiat Twin Cam engine in a Sylva Kit car. I junked the Fiat distributor due to chronic high speed misfire problems about two years ago and the car has been (and still is) running fine on Megajolt Jr 3

I removed the Eliott stepper motor tacho, which worked fine with the Megajolt, and fitted a TrailTech Vapor Dashboard. The car still runs fine but I'm having problems with the Vapor's tacho/shiftlight functions.

The TrailTech recommended install method is to wrap the tacho signal wire round a HT lead 5 turns, but this gives a very spiky reading. I've tried more or fewer turns (as recommended by TrailTech) and sheilding the wire, but no change.

I've tried a direct drive from the tacho pin of the EDIS module and from the tacho pin of the Megajolt, but the Vapor doesn't respond to these at all.

Does anyone have any experience with the Vapor/Megajolt combination?

Best regards..........Jonathan

Hello-

Do you have any documentation for this new dashboard you're using? Often, tachometers attach to the minus (-) side of the coil, detecting the high voltage kick-back pulse.

There is an adapter circuit listed here: http://www.autosportlabs.net/MJLJ_V4_ve ... back_pulse

if your dashboard can accept this kind of connection then this circuit may work for you.

Brent

The only docs available are the install instructions at :

http://www.trailtech.net/media/instruct ... ELV-07.pdf

and

http://www.trailtech.net/media/instruct ... e_tach.pdf

As you can see from the docs the dash is designed for ATVs and motorcycles.

The dash's tacho function is progamable to accept 2, 1 or .5 of a signal pulse per revolution.

There are lots of threads regarding tacho signal issues on various forums, but mostly for ATV or motorcycles, and the fix is usually a shielded signal wire, which I've already tried.

Best regards..........Jonathan

Johnathon

Option 2 of http://www.trailtech.net/media/instruct ... ELV-07.pdf would be best and set the unit to 0.5 signal pulse per revolution. Then just attach one wire to either coil A or B output of the edis

Or

Option 2 again set to 1 signal pulse per revolution event and run it off the PIP wire or the CTO wire (pin 11 if you have one).

N.B. I think i have the signal pulse per revoultion correct, i maybe mistaken but i guess it wouldn't take much to change it on the unit.

Ryan

All

Thanks for all your help on this, I finally sorted the problem.

I ran a wire with an earthed screen from coil pack pin B to the Vapor. This seemed to cure the matter until the car got warm in traffic one day and the fault returned.

The culprit is the electric fan, (originally from a '70s VW Polo) which is fully automatic on a thermoswitch, with no manual over-ride. Shorting the thermoswitch with the engine running but cold produces the same effect.

Given the distance between the fan and the dash, and the level of screening that I ended up using, the thing must have been putting out a huge amount of RFI.

It will now be swapped with a more modern fan, hopefully with better RFI suppression.

Best regards.........Jonathan

Interesting! thanks for the update. RFI/EMI emissions is often a culprit when odd behavior emerges.