What's the difference?

[Maverick H1L]

Need a bit of help here. Gone back to a stock V6 with distributor ignition as opposed to the DIS on the 3100 hybrid. Now my tachometer, from a 94 Camaro, is going absolutely nuts. I am very sure it's reading at least 1000 RPM high, and it's bouncing bad.

I have already replaced the ignition module in the distributor (because I thought that was the code 42 issue but it turns out not and the code is gone now anyways), swapped the ignition coil for another, replaced the spark plugs, checked all of the wiring, and just about anything else I can think of.

What is the signal difference between the 3x00 DIS ignition module and the distributor D1943A module? This is driving me nuts. I need to be able to set my idle speed but I can't if I don't know what the engine speed is... I'm trying to have this car back on the road in the next couple weeks here and this issue isn't helping much.

[Guest]

Did you re-install the tach filter? DIS systems don't need the tach filter between the ICM and the tach, because the signal is much cleaner and has less spikes due to not being triggered from the coil directly. Dizzy ignitions in '90's/'90's GM vehicles need the tach filter there to suppress spikes and clean up the signal for the tach.

[Maverick H1L]

You're going to have to explain that a bit as I have no idea what you're talking about...

I'm not going to swap the stock 87 tach I have into my 93 dash, that's for sure. And I'm not replacing the dash either (I don't have the heater parts for the other one).

[neophile_17]

You need this:

http://www.rodneydickman.com/n27.html

Or something like it. Otherwise the signal from the distributor has too much noise for your tach to interpret the RPM you're turning. I've always seen them installed next to the distributor.