FI Beta erratic tach?

[markalen]

Help has anyone already determined what would cause the tach to jump to arround red line in between any shift? The car runs rough at idle sometimes but accelerates ok. All the normal things have been replaced or checked, plugs, wires, cap, rotor etc. Any ideas?

[Gregory Smith]

You really, really need to pull the distributor and inspect the magnetic pickup inside. Mine ran fine and then started stalling occasionally. When I finally looked the pickup wires were nothing more than green corrosion and air, yet somehow it ran until then. Very disturbing considering all the places it could have left me stranded!

Another possible problem that I just tackled was the module, or so I thought. Turns out a previous owner had removed the ground wire from the module's heat sink, so it was only usually grounding via the strut bolts. I was ready to shoot the dang thing when I figured it out from wiring diagrams. According to the diagrams the ground wire is bolted tot he bottom of the sink, where the (radio noise?) condenser is bolted. I added a ground wire to the heat sink and it solved a very maddening problem. The poor ground would create enough resistance to heat the connection to the point it would fail. Over and over.

[Maigret]

A way of isolating the problem is to use a multimeter with a frequency (Hz) function.

By putting the probe on the relevant terminal on the coil the display on the meter should be 2x that of the tach.(for 4 cyl 4 stroke)

The tach receives the pulses from the coil so if one pulse is broken into 2 by a poor connection then the reading will be 2x normal.

As bud suggests, clean terminals etc and replace things like plugs (I do mine annually) and caps, rotors if necessary. I have cut terminals off and replaced with new ocassionally, a new one is only a few cents.

If you suspect the tach itself remove instument cluster, which is not difficult on Beta, and take to an electronics repair place. They can put a pulse generator on it and calibrate it exactly. I had a 4 cyl tach converted to 2 cyl and the tech did it while I waited.

[Jim Keller]

I'm with Greg, better order a pickup coil and don't drive it anywhere you don't want to pay a tow bill on to get it back home until you get that fixed. It will just suddenly quit running after a while. 8O

[markalen]

Thank you for the information, I will be picking up that module. As always, this group is wonderful.