ok so just got my car back on the road, and i noticed under light throttle the tach jumps up an down about 500 rpm more severely around 2000RPM.

now the car runs fine and dosent miss.

this occurred just after my new accel coil and ignition module was installed. i made a new bracket for the coil the stock one was all messed up. and the 2 wire plug from the cap to coil is tight across the front side of the cap.

now i know the tach boards go bad and cause them to act funny. i have a second board i can try but i want to know if there is anything else that can cause this IE coil interference ect, also which wire is responsible for the tach signal from the dizzy. any help will be greatly appreciated. i want to put in an msd 6a box however id like my tach to work correctly before hand so if the msd messes with the tach as they some times do i can fix it knowing its just the msd.

thank you p.s i have read https://www.thirdgen.org/forums/elec...meter-fix.html

just want to try other ideas first

 

check all ur grounds batt to block,block to fire wall,alt,ecm,try running the car and feeling the grounds by hand if theres a bad connection they sometimes feel warm or even smoke

 

will do im going to look at it when i get off today. also i believe it only jumps while actually driving i can hold it a 2000 in neutral and it doesn't seem to jump. that leads me more to some kind of interference

 

sounds like a bad plug wire.

 

Yep. I had an old Jeep and when the tach bounced and the engine didnt miss, the plug wires were bad.

 

hmm thats very interesting.. ill check the wires as they haven been on there for almost 2 years i have headers and no heat protectors. maybe when the bad wire gets hot it causes interference of some kind. ill deff check it out.