Stock Tach and TBI Revisited
was searching past archives and noticed a thread on Stock Tach and TBI and made me start thinking about how i wired my HEI and Howell TBI kit. so here's the scenerio -
i installed the HEI before the Howell and and my stock tach was actually working perfectly (didn't think much about why at that time). i was drawing power to the HEI power directly from the 13F red wire. according to what JAFFER said regarding the 13F red wire being connected to the 13C red wire into the tach, i think the stock tach was still reading the Power pulses from the 13F/13C wire when the HEI fires the sparkplugs hence allowing the tach to work just fine.
now since i installed the Howell kit, my tach has been an order of magnitude off in the RPM readings. tach needle movement still correlates with accel/deceleration but i don't "idle at 1200 RPM and cruise at 3200 RPM". only diff in wiring is that i'm also drawing 12V power for the TBI Computer ECU from the #13F red wire along with the HEI.
the question: does the ECU also "pulse" the #13F wire (maybe pulse correlates with injectors firing?) or does it draw Power at a constant rate? i'm wondering if connecting the ECU to #13F wire is causing the "extra" RPM readings i'm seeing on my factory tach and if i wired the ECU to some other 12V ignition triggered power source, i woudl revert to pre-Howell install scenerio where the tach only "sees" the Power pulses from the HEI firing the plugs...
btw, if you do a search on "factory tach and TBI problems" as subject, you'll see the bbs thread i'm referring to...
83 CJ7 258/T5