intermitent ignition problems

[Matthieu]

Hello all!

i've bought 2 mounths ago a electronic ignition (123 ingition) for my 74 3.0 CS.
It was a real improvement, linear acceleration and it goes upper in rpm.
but 2 weeks ago, while I was driving smoothly, i experienced a 'cut out' with no warning of the engine and the tach went brutaly to 0.
It is very unpleasant to experience this on the road.
I tried to restart the engine with no success.

There were no sparks in the plugs.
I first thought it was the electronic ignition. But it seemed to be somewhere else, like a poor ground.

The car restarted 2 days after with no problem (!?), and had intermitent stops.
I had little 'cut-out' during the acceleration. and big'cut-out' of the engine. Not good to go for a ride...

It might be a wire grounding somewhere. But no way to find where.

So it disconected the tach wire from the '-' of the coil. (black wire).
And the ignition problem disappeared. But the tach is not working anymore.
It might be a wire grounding in the tach or something like that.
I can drive the car but i can not connect the tach wire without having ignition problems

--> Does anyone has already experienced a problem like this?
Do I need to remove the tach to find a wire grounding?
Thanks a lot!!!

 

[sfdon]

Very likely your tach wire has gone bad as it runs around the front of the car and into the dash.
You can replace it fairly easily.

 

[jmackro]

I would de-bug this by making a temporary jumper wire to run from the coil "-" to the back of the tach (yea, the back of the tach is real easy to access!). If the car runs reliably with that in place, then sfdon's diagnosis is correct - the factory wire has gotten pinched somewhere, creating a short.

But are we certain that the 123 is compatible with the BMW electronic tach? Is it possible that the tach has somehow fried itself while driven off the 123, creating a short? E.g., have others run a 123 successfully, with the stock tachometer in place?

I can report that my Pertronix drives the stock tach with no problems - I would expect the 123's coil driver to be similar to a Pertronix.

 

[Stevehose]

No issues in 2 years of running the 123. One of best upgrades I've done for the car.

I would de-bug this by making a temporary jumper wire to run from the coil "-" to the back of the tach (yea, the back of the tach is real easy to access!). If the car runs reliably with that in place, then sfdon's diagnosis is correct - the factory wire has gotten pinched somewhere, creating a short.

But are we certain that the 123 is compatible with the BMW electronic tach? Is it possible that the tach has somehow fried itself while driven off the 123, creating a short? E.g., have others run a 123 successfully, with the stock tachometer in place?

I can report that my Pertronix drives the stock tach with no problems - I would expect the 123's coil driver to be similar to a Pertronix.

 

[Matthieu]

Thanks Jmackro! I'll try to jump a wire from the tach to the coil.
but how can I access to the back of the tack? Is it possible to remove the tack without removing all the dashboard?
It seems to be a big task to remove all the dashboard...!

thanks a lot!

 

[jmackro]

Yes, it is possible to remove the tach (and other gauges) without disassembling the whole dashboard. There are several threads on e9coupe.com that discuss this - here is one example: http://www.e9coupe.com/forum/threads/speedometer-instrument-removal.15607/#post-107171 You can find similar threads by searching on a phrase like "gauge removal".