I have a '79 C30 with 454. I get missing and lose power around 2500 rpm. My tachometer loses power when this missing occurs and drops to zero. When I let up on the gas pedal and the rpms come down a little the missing subsides and the tach returns to normal. I have replaced the distributor cap, rotor, coil, spark plug wires, ignition module, and vacuum advance. Timing is set at 9 degrees before TDC at hot idle with the vacuum advance disconnected. Spark plugs all look good and are gapped at .035
Anybody have any ideas on what I should check next?
I have thought that maybe there is resistance in the 12V supply wire going to the distributor or maybe there is resistance in the harness.
Does anyone have any resistance specs that will help me diagnose?