Jumpy tach and miss

[Sensei]

My car, with stock '81 CCC ignition + an MSD 6a box has developed an intermittent miss, accompanied by the tachometer needle jumping erratically. It will run fine sometimes, then the tach starts jumping (bouncing upward, not cutting out) and the car feels like it is running on 7 cylinders, then it will run fine again. I disengaged the MSD and that made no difference. The coil, cap, rotor, plugs, wires, ignition module and distributor are all good quality and only a few months old. With the problem being intermittent, I have not been able to troubleshoot it. Has anyone ever had what I am describing, and what caused it? Thanks and God bless, Sensei

[hdkeno]

Sensi,

My 81 did the same exact thing as your earlier this year,and I had to replace the ecm,as the original unit was inoperative,no check engine light.

When the new ecm was installed,the problem was a bad throttle position sensor.

Since then,car runs like new.

But prior to,i experienced all of the conditions you are having.

Tach would jump intermintantly,then she would start bucking and seem like to run on 7 cylinders etc.


Good Luck, Ken

[Sensei]

Did your ECM show a code once it was working, because my ECM is working and no code. God bless, Sensei

[hdkeno]

Yes,Sensi, it did, forget the code #.But it was showing a faulty tps,throttle position sensor,which is in the carb.

replaced that and all was well. Hope this helps.

Ken

[Dave L.]

Originally Posted by hdkeno

Sensi,

My 81 did the same exact thing as your earlier this year,and I had to replace the ecm,as the original unit was inoperative,no check engine light.

When the new ecm was installed,the problem was a bad throttle position sensor.

Since then,car runs like new.

But prior to,i experienced all of the conditions you are having.

Tach would jump intermintantly,then she would start bucking and seem like to run on 7 cylinders etc.


Good Luck, Ken

Same problem developed with mine last fall. Same findings as hdkeno.

[John Ulrich]

I just replaced my "control module" (under distributor rotor). This was the second one in 2 months. Started to miss, then the back fire was the last straw. I'm hoping this one works long term!
JU