512BBi tach problem

The tach seems to be dead when starting the engine cold, but starts working a little later when the engine warms up. Tried switching the tach with a known good one, same problem. Is there any trouble some connector somewhere that may be the cause? I assume the tach receives it's signal from the Marelli box.

 

There is a connector at the instrument pod, but I'd put a lower probability on that being the root cause (but still could be). The tach signal on your model is a signal "generated" within the DinoPlex ECU, but many have been reported as being replaced with, for example, an MSD brand ECU -- do you still have the stock DinoPlex ECU in place?

I can't recall anyone reporting before that the tach signal failed but the primary function of firing the coil still worked on their DinoPlex ECU -- usually it's the primary function that fails . If you do a search on "DinoPlex" by user "alhbln" you should get a lot of technical threads on DinoPlex -- and some of them should list Adrian's (alhbln) DinoPlex website that might have more detail information regarding the tach signal.

 

Steve, it still has the OEM Marelli ECU, so I am leaning toward the ECU for the poor tach signal generation. If that is the case, then replacing it is not an option. I will check the web site referenced. Jim

 

Remove the Dinoplex rev limiter (the small box on top with the RPM label) and clean the contacts with contact cleaner, then reinstall and try again. If this did not fix the problem, change the tach wire at the Dinoplex connector from terminal 5 to terminal 4. If this still not fix the problem, your tach wiring from the Dinoplex to the tach might be broken.

Good luck,
Adrian

 

Had a similar problem years ago on my 83 BBi and it was the Dinoplex. Back then you could source a replacement for a not so unreasonable price which is what I did.