[patman]

I have an Auto Meter 3911 Sport Comp tach that I bought used a couple of years ago, supposed to have been working, don't remember who I got it from. When I got the new engine in, the ancient Sun Super Tach II had in the car previously didn't work with the Digital 6 Plus ignition box, so I recently put the Auto Meter one in. As soon as I flipped the key to 'on' and it powered it up, the needle flipped to 7K and sat there wiggling...the engine wasn't even running yet. I've currently got only the +12 and ground hooked up. No trigger, no lights. Same symptoms. Either there's a BUNCH of noise in the +12 from the MSD box (With the engine off?!?! I'm about ready to break out the oscilloscope) or the tach is toast, or...???

Anyone seen a problem like this before?

 

[chevyIIheavy]

your old tach needed the msd tach adapter part # 8920 your new tach has the shift point set at 7000 rpms check to make sure its set up for a v-8 cause sometimes they will be on the 6 or 4 cylinder adjustment. if you start the car does it come back to zero and then your car fires up does it read the idle of your motor or does it bounce all around as well

 

[jarhead64]

Not sure if you have the installation instruction for this model but here is the link for them - http://www.autometer.com/cat_gaugedetail.aspx?gid=3335&sid=11

One of the comments in the trouble shooting section is " Disregard tach readings that occur before engine is started".

 

[patman]

your old tach needed the msd tach adapter part # 8920 your new tach has the shift point set at 7000 rpms check to make sure its set up for a v-8 cause sometimes they will be on the 6 or 4 cylinder adjustment. if you start the car does it come back to zero and then your car fires up does it read the idle of your motor or does it bounce all around as well

I know I could have gotten the adapter transformer for the old tach, just didn't want to go that route at the time. The shift point is not the issue, I've tried (re)setting it, and that seems to have no effect. I was pretty sure it was set up for 8 cyl, but...good point, I'll double check that. I tried starting the car last night, and it went a full turn around, and the needle was still jumping around. I'll give it another shot though.

Not sure if you have the installation instruction for this model but here is the link for them - http://www.autometer.com/cat_gaugedetail.aspx?gid=3335&sid=11

One of the comments in the trouble shooting section is " Disregard tach readings that occur before engine is started".

Yes, I have the instructions. Hmm...didn't catch that note though, maybe I'm being too picky about it not reading ZERO!!! How hard can that be?

 

[patman]

Got it fixed tonight. Turned out to be a bad power connection, so it wasn't getting a full +12v. I found something on their tech board that mentioned that it would read high if the voltage was too low, and tracked it down from there.