Quote:
Originally Posted by mach4
The fact that the diagram shows two "paths" to the tach module from the pickup is pretty strong evidence that the EGR is just a "pass thru" connection and has no role in signal processing or conditioning. This is further evidence that bypassing the EGR for the tach signal as has been done many times is a good solution not just an "it works" solution. I always suspected this, but never opened the EGR to trace the connections.
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I can assure you the tach pickup to my 85 EGR controller is not a pass through. It comes in the EGR controller as a sine wave and goes out as a square wave to the cluster. I did ask andrewjtx (question was unanswered) in this thread
Quick Fix: 1985 w123 Tach & A/C after EGR Failure how he ever came up with the idea of by passing the EGR controller. I think someone must have messed with an 84 tach and saw that the bellhousing sensor went directly to the cluster and decided to bypass it on models with an EGR controller and found that it worked. It'd be interesting to see what the resistance of the 84 tach pickup is. I am betting it is the same as an 85 at around 1.6K ohms (1600 ohms).