Just recently my tach has been acting up. It works fine most of the time but when I floor it the tach needle bounces back and forth along the entire range and then goes down to 1000 rpms or less. I can hear the engine accelerating so I know something is wrong with the tach. What does the tach get it signal from? Altinator, distributor, something else? I have recently installed a new accel coil, accel ignition module (same thing happened before and after the ignition module) an MSD 6A and new plug wires, although I dont think the tach has much if anything to do with these things. Maybe the MSD if the signal goes through that somehow? Thanks for the help!

 

Yep, chances are the MSD box is the culprit. I've got a Digital 6+ and had to drive my in-dash tach from the tach terminal on the MSD box. I don't know if the 6A box has that or not. Check if you have a tach filter on the firewall, if so supposedly you can splice the tach wire around that and work fine as well.

Hope this helps you out. You can call MSD about this as well, but chances are they're gonna sell you a "tach adapter" that would probably work fine but may not be required for you.

 

Your new coil might be the problem, the Tach gets its signal from that using the white wire from the gray connector.

 

Possibly, Trickster, but chances are the multi-strike signal is what's causing the tach to get all confused.....

 

As it says in the MSD instructions, you have to use the tach terminal on the box to drive the tach.

 

Ok I dont have the MSD 6A instuctions. I bought it used. Which is the tach termainal? I have added an MSD box without using a tach terminal but it was a MSD 5 and one time with an MSD 6A but that was on a 327 mtor in the 85 firebird.... no comuter and a basic chevy coil set up... on 2 wires instead of 4. Also in the set up I used the MSD connecting harness to keep from splicing wires and no only 1 of the 2 connectors attach directly to the coil.

 

http://www.msdignition.com/pdf/6series.pdf

The tach terminal is a male quick disconnect terminal on one end of the box, if i recall correctly.

 

Thanks for the information. According to the MSD instuctions you sent it says to bypass the tach filter. Where is that and how do I do it? According tho them they decribed the same problem I have and say that how to solve it.

 

Are you using the tach terminal on the box? You might not even have a tach filter.

 

No I am not using the tach termanial on the box. The MSD directions say not to use it. It says to just bypass the tach filter. If I decide to use the tach termanial on the box the stock filter would still be inline and causing the problem. So where is this tach filter? What does it look like? Please help!! I followed the white wire on the grey connector from the coil and along it was a grey 1 wire connector in the middle of this wire for no appartent reason .... unless the connector is the tach filter itself? I have no clue? to bypass it would I just cut it out and connect the wires with a butt splice connector? If this is not the filter ... does anyone know where it is and what it looks like! Thanks!!

 

On my 89 camaro, that gray connector you are talking about is a tach diagnostic connector for checking the RPM's as they come off the ignition coil.

 

The tach filter is located in the loom(harness), hidden a short distance from the coil connector on a 5.0 E Vin 92RS. Hope this helps. Good Luck

 

I think that grey piece is the filter. I just got a MSD 6A and had the same problem. I disconnected the filter and connected the tach terminal on MSD to the white wire that goes to the tach not the coil. Leave filter disconnected. Everything works great. No codes, tach reads over 3000rpm.