Hello,
I have a 1999 cavalier with the 2.2 liter engine in it. It is a 5 speed manual, and i am slowly working on tuning it. I recently purchased a sunpro tach and adaptor. the problem is that with everything hooked up according to the instructions (black to ground, red to ignition in fuse box, white to lamps, green to adaptor, and on the adaptor the red wire to the white one on the coil pack plug and the black to the orange on the plug.) The needle on the tach goes to zero and stays there for several miles then starts reading normal. I have let the car sit and idle for half an hour and the tach remained at 0-250 rpm, so i beleive it has something to do with the tach needing to warm up. I just cant figure out why it does this. All connections are solid, the adator has signal through it, and the voltage increases when the gas is depressed. The ground is run straight to the battery because i was getting interference using grounds in the dash. I am using the sunpro cp7906 tach, and I have seen the same tach used on youtube videos and the needle shoots right to idle speed when the cars startup. I even exchanged it and got another new one just in case the tach was bad. Is there any other way to hook this up? or am I doing something wrong.

Any help would be appreciated. I even exchanged it for a new tach thinking i had a bad one, but the second one went backwards and would stick. Now i am on the third and it is sitting at 500 for idle and doesnt seem to want to go higher than 1k rpm when driving. using a multimeter i get a reading of .25 volts from each ignition lead, and on the output from the adapter i get a reading of .5 volts at idle wich jumps when i apply gas. I just cant figure this out. is driving me nuts

sounds like a problem with your adapter, which adapter are you using?

also, what is the tach set to? how many cyl?

The best advice I can give you is to find an Autometer 9117 Tach Adapter if you're using the RKsport Tach Adapter, that solved all my tach problems. They can be had for around $40 used on eBay.

I am using the Sunpro tach adaptor. Apparently there is a tach lead in the pcm. I guess tomorrow i get to tear apart the wheel well to find it so i can test the tach on that lead. If it works from that lead, i will assume the adapter is bad. If no, then I will have to assume yet another bad tach, and try a more expensive one than Sunpro.

Well surprise surprise! the tach adapter did it! The damned cheap ass sunpro tach was made with only diodes to prevent the signals from crossing. For some reason it took the diodes while to warm up and let the signal through. So I dug under the wheel well to find the pcm and was dismayed to find no wire from pin ten to tap into. So after some colorful expletives, i decided to go to radio shack and pick up some pins that may fit in the connector. big surprise when they didnt have any, but i found some but connectors that were just about the right size. a pinch here and crimp there made it snug. Long story short, it was a pain in the ass to connect the tach, but it works. thanks anywasy guys, your tips got my gears working, metaphorically that is.