Hi all, I haven't been on chat for quite some time now, but it's always the first place I come to for advice because of the vast array of knowledge here. Here's my question...I have an 86 328 with @ 30k mi. on it and just last night the tach started reading half the rpms. I assume there is a sensor on each distributor and is combined and displayed by the tach. I'm thinking maybe a pick-up is dirty or bad. Is anyone familiar with or have seen this before? The car runs great otherwise. Any help would be greatly appreciated. thanks, LUCH
Lots of good info on this. You're not the only one with the problem . I replaced mine a few months back. Check out: http://ferrarichat.com/forum/showthread.php?t=19935 and http://ferrarichat.com/forum/showthread.php?t=10216&highlight=tachometer Take care, --Mike
I have an 1986 328 GTS and after replacing the sensor and rechecking all the connections the Tach read about half the RPM's and the speedometer read about twice the MPH. Since I knew my car wasn't that hot I sent both instruments off to Palo Alto Speedometer. PA Speedometer did a great job, for a very fair price. Turn around time was less than a week, and now both instruments are dead on. They said it was a chip that goes bad on a lot of those instruments.
The 328s have two sensors on the flywheel: one for RPM, one for TDC (2 pulse per rev). These are fed to the Marelli Multiplex ignition computer, which sends the tach an RPM signal. A separate sensor, driven by the gearbox oil pump (on the output shaft) sends a speed pulse train to the speedo. If the sensors (or computer) is bad, the engine wouldn't be running "great". It might be a driver chip in the computer, but it's more likely the electronics in the tach instrument itself, as described in the other messages, above.
Yup, remove the tach and send it off to a speedometer repair shop, of your choice. Palo Alto Speedometer has a lot of experience with this. For some reason, ALL the 3.2 motor tachometers fail....apparently there is some component(s?) that go bad...Anyway, mine was fixed by PAS about 1.5 years ago....still working fine. Dave