Electrical 88 5.0 Tach diagnostic help

Deydey88

New Member
Sep 25, 2019
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Costa Mesa, Ca
First post here. I’ll get straight to business.

I have a 1988 5.0 Im currently restoring and the tach is dead. I have removed the whole harness during the resto and gone through it from the ecu to the engine. The tach only moves when cranking the engine to about 100-200 rpm. I have tested the 22k resistor and it checks out fine. I have gone as far as taking the tach apart, re soldering pins for hope but all traces looks ok and unbroken. I even replaced 2 swollen capacitors on the pcb for the hell of it. I have tried another tach from a different cluster and had the same results. Ive tried different coils, added more grounds to no avail. The laminated circuit board on the back of the cluster is in great shape. All other gauges work great. Car sat for 17 years in a garage. No codes with KOEO and KOER. Ironically a System ok code 11. Only problem is theres still a problem!

Instead of guessing I would like to know what to test next and what if anything I missed. I know my 22k resistor is good. The DG/Y wire tach feed from the coil to pin 11 on the grey cluster connector is in one piece, What am I missing here? Is there another piece to the circuit? All help much appreciated for my sanity.
 
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