Daytona sensors smart spark ls tacho problem.
 

On my 82 trans am with all 92 gauges the tach will read 1000rpm roughly but when revving it drops to 0. The tach always worked with the old sbc in the car. I also tried my 3 spare clusters and all do the same. The tach is a 12v square wave unit. All the replies I get grom DS say gm early tachs are 5v. These are not. They are directly wired to coil - from the factory.
I checked all wiring. It's all good. It must be something with the smart spark "*(
Does anyone have an idea what's going on? Testing as ac voltage shows a pretty constant voltage. It does not climb up from the 10v but my dvm might be too slow although I think it should still show a higher reading as rpm increases. I'd hate to wire in a dakota digital box. I already have 1 for my speedo and could really do without more wires.


Here's what it does. It reads a little high but that's always the case with these tachs.


For the rest the smart spark works flawless and logging does show correct rpm

Tnx

Marck

Try a pull up resistor

https://www.autometer.com/resources/...faq_view/id/77

What good would it do. DS says the output is a 12v square not a 5v. The signal might be too clean a square as what comes originally from the factory coil is a very sloppy peak with a lower voktage retention then drops off. Sort of a heartbeat. I can simply try the pull up but been thinking about dumbing the signal down with a zener.
Also a factory tach can't be set to 4cyl. I guess if the zeners don't work the dakota digital box is the only solution.

It allows calibration of the tacho also

I don't have an ecu with a 5v tach output to use a pullup on

Because maybe the box can sink more current than it sources,

Pretty easy to build a tach amplifier. Using an optoisolator will remove any sort of grounding issue as well. I would also try connecting a known good tach.

But since your convinced it is the box contact the guy at daytona systems and ask them. They have an excellent reputation for customer support.

By the way I had a similar problem with my 240z tach and an MSD box. Tach worked fine at cruise but above 4k rpm it would start randomly cutting in and out. Did it with two different stock tachs. I tried every type of tach driver circuit I knew how to build. My speedhut tach/shift light never had the issue. In the end I gutted the stock tach and built new internals from an arduino and a GM stepper motor. Have to wonder if some of these old mechanical tach motors just need more juice as they age.

The tach is an air core type. I'll try anotger tach. As for cust service. I got a short answer "we never had issues w aftermarket tachs" after weeks. Not helpung a lot at all.

Sorry to hear that. Guess their customer service rating just dropped a few notches.