Tach Issues with stock ECM

[Tincup]

Anyone running an aftermarket Tach with the stock ECM? How did you hook it up?

 

[67Dart273]

Hook to the coil negative, it should work just fine

EDIT Didn't catch this was in the "new hemi swap" section

 

[Gdemon]

Hook to the coil negative, it should work just fine

If it was only that easy. lol. I have one on mine using the factory dash tach. Im using a converter from dakota digital. SGI-8 with a MSD magnetic pick up so i didnt have to cut into the coil harness.The Dakota digital box was about 90 bucks and the MSD pick up was about 70. Mine seems to be about 100 rpm off at idle and about 1000 rpm off at 6400. Not sure if its the tach or the converter. Autometer makes one but you have to cut all the coil wires. I need to try another tach to see if its the tach or converter.

• http://www.hotwireauto.com/?page=supportHow do I get a tachometer signal from my Hemi system?
  • Clip an MSD GMR Pickup (p/n: 8918) to one of the pink/yellow coil wires to get the signal. Set your tachometer to '2'. If your tachometer doesn't have this setting then you can use a Dakota Digital SGI-8 signal processor to multiply the signal x4.

Here is the reply from autometer.

In order to wire in a tachometer, it will require a #9117 Auto Meter tachometer adapter. This requires re-wiring the power for all 4 coils on one bank. From the factory, you can not cut just one wire to affect all 4 coils, since the injectors use the same powers as the coils, and the coils need to be separated from the injectors.

I have included a write up from a factory application. Keep in mind the color of the power wire is likely different.

Will Need 9117 tachometer adapter. Recommend only experienced technician for this application! Will have to cut brown wire with a white stripe at each of the 8 coils. Wire all 8 coils together going from coil to coil. After all 8 coils are wired together, hook to red/green of the tachometer adapter. Hook the solid red of the adapter to the original power source for the coils. This way all 8 coil draw their power through the tach adapter without interference from any other components.

The write up speaks of cutting the separate power to all 8 coils, but I have found that in many cases you can get away with cutting of just one bank due to Chryslers wasted spark system.
Thank you.
Cory
Tech/Service​

 

[Tincup]

Thanks G, those are the same two options that I have found. I also found a link at Street & Performance on how to hook up the MSD & Dakota Digital setup, maybe it will help you find your error. I also talked with Chris at Hotwire, he said to set the SGI-8 to mutiply the signal X4, and set your tach for an 8 cyl.

http://www.hotrodlane.cc/ONLINETECH/HEMI%20tach.pdf

 

[boden]

My gauges are from Speedhut. When I had mine running for testing it seemed to be working fine. I connected one wire to a coil pack and if I remember correctly I had to set the tach to .5 pulse per revolution. I never really checked it too close for accuracy but it seemed to be on target. It also has an extra wire that you can cut to increase noise immunity if the tack seems a little jumpy. I'm not sure if I will need to do this. Their website says they make the only tach that does not need any special adapters for distributorless ignition systems.

http://www.speedhut.com/custom_gauge_description-gauge_type-Tachometer-auto_number-803.htm

Installation instructions:
http://www.speedhut.com/support/ind...rticle/View/34/5/3-38-tachometer-instructions

Hopefully I'll get enough bodywork done this summer to put it back in and have it running again.

 

[5.7 hemi]

Tin, I just checked the wire harness we have the same thing) and the YELLOW goes to the tach, then you need a power and ground. Then it should work just fine. What gauges are you running? I'm using Dolphin, and they work perfect.

 

[Tincup]

My gauges are from Speedhut. When I had mine running for testing it seemed to be working fine. I connected one wire to a coil pack and if I remember correctly I had to set the tach to .5 pulse per revolution. I never really checked it too close for accuracy but it seemed to be on target. It also has an extra wire that you can cut to increase noise immunity if the tack seems a little jumpy. I'm not sure if I will need to do this. Their website says they make the only tach that does not need any special adapters for distributorless ignition systems.

http://www.speedhut.com/custom_gauge_description-gauge_type-Tachometer-auto_number-803.htm

Installation instructions:
http://www.speedhut.com/support/ind...rticle/View/34/5/3-38-tachometer-instructions

Hopefully I'll get enough bodywork done this summer to put it back in and have it running again.

Thanks Boden, but I bought my gauges a long time ago, I have all AutoMeter Carbon Face Gauges. Any questions on the body work, just ask.