[Vwdiesel] Erratic Tach

Roger Brown r.c.brown at ieee.org
Thu May 31 19:20:05 EDT 2007

Dave Heart wrote:
> Has anyone come across a stock jetta gasoline tach that works fine for 
> about 15 minutes then becomes jumpy and finally stops? Always works fine 
> when engine is cold. I have been using Roger Browns basic design to 
> allow cruise control and gasoline tach in my camper diesel pickup. Have 
> tried relocating electronics away from engine heat to no avail. The 
> jetta tach was a used one.

Two likely causes would be the voltage stabilizer on the back of the cluster PCB.  Do the 
other gauges work fine?  Other thing might be a loose wire at the back of the tach, maybe 
the vibration gets to it with engine operation.

On my '82, I once had the tach cut out and I thought it was heat related (on the way to 
Las Vegas).  Turns out the power or ground wire connection I made at the injector pump was 
loose and I guess with the heat and vibration, it would cut in and out.  Tightened the nut 
back down and it was fine.



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