factory tach began fluctuating and then died

[Incommando]

'91 OBD1 4.0. Looked down and the tach was bouncing like crazy but the engine was smooth and just like it should be. Then the tach just quit reading. I checked the dist.connections and they are tight. No other electrical issues.

 

Ideas?

[AeroNautical]

Maybe the tach itself failed? Does the tach read from the distributor? I figure if the engine runs fine, it can't be anything to do with the ignition coil or distributor. I thought the tach read from a different sensor all together. 

[HOrnbrod]

On the HOs the factory tach gets it's signal from the ECU, pin 43. Not the dist. Unscrew and pull the 60-pin connector off the ECU and check for corrosion, and/or recessed pins (#43 to be precise). Douche it down and clean it up with some quality electrical contact cleaner.

[johnj92131]

On the HOs the factory tach gets it's signal from the ECU, pin 43. Not the dist. Unscrew and pull the 60-pin connector off the ECU and check for corrosion, and/or recessed pins (#43 to be precise). Douche it down and clean it up with some quality electrical contact cleaner.

 

How about the plug on the cluster?  May want to try that if cleaning the ECU doesn't get the job done.  All else fails, try a different tach.  Think I have a couple of extras.  If you want to borrow one, drop me a p.m.

[Incommando]

Thank you to you both. I think I will pull the cluster as I just swapped it in a few months ago. It would be more likely that I screwed something up. :)

Thanks for the info on the connector, Hornbrod. That will make it easier for sure.