tach board question

[gravismaximus]

for the last two summers ive had a intermitint problum and have figured out what is happing---kinda i rebuilt my engine 3 years ago the first year was flawless preformance, the like i said 2 years ago id be driving and my tach gage would drop to 0 and engine would stall, howerevr i hardly ever came to a stop befor my tach gage would jump back up and the engine would come back to life again and pressing on the gas pedal seemed to help bring it back somtimes. and down the road id go untill it would happen again. it did seem to happen more on hotter days, so i replaced the distribtor, ign moduel, and put a another high preformance hei on it. didnt help i found out when i was driving it last year. and one day it just quit on me at work. as i was trying to diag it i found that the tach wire on the hei when wiggeled it would cause the car to stall... now form what i was taught in my automotive collage and all my years experiance with cars ive never run into a hei system that needed a tach to run, but i said maybe it is a corvette cause at the time i didnt have a wiring diagram. so i replace the connector and the wire from the back of the printed circut to the hei. while i was there i noticed that the printed circut on some edges was starting to peel, but the copper lines where all good looking, so i taped the edges back together and i also tried making the tach gage itsself work and i blew it up, (note to self dont make a short to power on the board) so i took it and had it rebuilt, seemed to work good for a couple of days then the problum came back again. and it was time to put it up for the winter, over the winter i changed jobs and talked with the new shop guys about it and my manger says to me you dont need a tach wire to make the car run, i replied i know your not spose to but i have a witness that my car woudnt run when i unpluged it. so we unpluged it and of couse it RAN making me look stupid. and hasnt missed a beat scince over a month. so what ever the problum is its shorting out my coil and it has to do with the tach, board, or printed circit. i dont have the 300 for new right now seeing how im a new daddy. so i went on ebay and saw a tach gage and board but on the guys entry it says for non special performance engines. so now here comes my real question (sorry for making read so much) where do i get a gage/bord for a hi performance engine? mabye thats the real problum the tach gage is back feeding into my coil killing it for a couple of seconds. is this common ive never heard of it but, please give me any new ideas.

 

[wishuwerehere82]

That sounds more like a short to ground rather than an open circuit from the tach signal to the ECM. Or since the tach connector is next to the battery connector on the HEI, maybe your battery connector is loose too. The spade connectors that come out of the distributor cap can work their way back inside the cap after a while. If you take the coil cover off, you can push the connectors back down where they belong.

 

[Jack]

Like wishyouwerehere82 says ... look at BAT & TACH terminals ... they're VERY close to each other. Alotta folks no longer have the correct, insulated pigtails at dist cap ... alotta folks simply have bare female terminals slipped onto the caps male spades. HEI can & will jump fire between unshrouded BAT & TACH terminals.
JACK:gap

 

[goertz]

someone else is having this same problem. you might also want to look for a shorting tach wire. if it shorts to ground, it will ground the entire ignition system, and the car will die. sounds like when you move it around, it shorts, or the batt terminal doesn't have a good connection at the distributor, so disconnecting the tach disturbs the power wire to the distributor.