Tach very bouncy!!

miniboo · Post by **miniboo** » Sun May 04, 2008 5:33 am

I have connected up my rev counter to the output from megajolt.

It works but it is very bounucy and also when coming off the throttle it tends to zero then go back to normal or if i am on part throttlewit goes to zero.

Should i be using a different method to run the tach?

It is an old smiths tach i think.

910esprit · Post by **910esprit** » Sun May 04, 2008 3:50 pm

I have the same problem on Smiths Tacho Read WHOOPS thread.

I am going to try the fly back method as this is how the Tacho was driven in the origional installation.

I will post if it works.

advantage998 · Post by **advantage998** » Mon May 05, 2008 6:04 pm

Its weird mine only does it when the advance is higher than about 32 degrees.

Why would this be?
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Post by **brentp** » Mon May 05, 2008 6:30 pm

The pulse-width of the tach output varies with ignition advance since it piggy-backs on the SAW pulse emitted from the controller. Some tachs, like yours, won't see the signal if the pulse-width is too narrow. In these cases you'll want to use one of the alternative methods for driving your tachometer.

Paul f · Post by **Paul f** » Tue May 06, 2008 10:12 pm

I am running a Smiths tacho using the pip signal.I had a problem with the diode circuit due to the zener breaking down and causing a missfire , so I tried the pip signal and it works perfectly.
Paul

910esprit wrote:I have the same problem on Smiths Tacho Read WHOOPS thread.

I am going to try the fly back method as this is how the Tacho was driven in the origional installation.

I will post if it works.

910esprit · Post by **910esprit** » Wed May 07, 2008 8:10 pm

I have tried the fly back method and the tacho works up to 2000rpm then drops to 0.

removing the Zenner diode causes the tacho to stop working.

Removing one of the diodes and the tacho works but as you would expect only shows half the reading.

are there any down sides in using the pip signal?

Post by **brentp** » Wed May 07, 2008 9:21 pm

The PIP should be fine even if it's driving the tach and the MJLJ PIP input. Just verify the MJLJ can read RPM in a stable way- stare at the screen for a while, or just do a datalogging session. If you're satisfied then you should be good for a permanent fix!

910esprit · Post by **910esprit** » Fri May 09, 2008 8:22 pm

Success!

Wire Tacho to pip signal and very stable and responsive tacho and MJ tacho readings stable.

Thanks for the Help another Happy MJ user.

miniboo · Post by **miniboo** » Sun May 11, 2008 9:28 pm

so i can just tap into the PIP signal? think i need to read the wiki again