Has anyone had a shift light tachometer cause ignition problems? I was told that something can go wrong internally and that it can cause a car to not even start among other problems!
I have an Autometer shift light tach and a MSD digital 7 ignition and although the tach seems to work great I occasionally have a slight miss just as I shift from 2nd to 3rd.gear -occasionally on the 1-2 shift. That is the only time I have this miss.At no other time does it miss. Right at the shift point. It seems RPM dependent! I shift at 6500 and I have the upper rev limiter set at 8000. 2 step set at 4500 with no problems.Floats set 1/2 in window,fuel pressure at 7 psi, Magna flow 500 with return with 1/2 in. lines to front with 3/8 to carb.
I have already replaced the MSD box,coil,distributor,wires,plugs, all relays,fuses and associated wires and grounds, Carb,fuel pump,filter,all fuel lines,fuel cell(no foam in fuelcell,)vents,intake and carb gaskets.Cleaned the fuel cell and fuel pressure regulator also.

Just looking into if I should try and replace the tach also.


Thanks Mike
Thanks Mike

I remember reading something about one causing a miss.

I had a problem with mine, turned out to be the tach ground wire was loose.

I had a cheap tach do that, but I had a two step cause a problem like that too.

RC91 did you have a miss just when you shift? How did you cure the problem?
Thanks Mike

Mike,
I have a problem very similar to yours, but I've never thought about the tach being bad.
Mine feels like its missing right at the top of the gear changes (5800 w/ RPM activated air shifter) and sometimes in the speed traps (depends on track). I finally figured out it was the rev limiter kicking in for just a split second. I can pull the high side chip out of two step and the "miss" goes away. I was thinking it was in the distributor, but it could be my tach? My tach is a Autometer monster tach with shift light, about 21 years old. I will change it this week...
Brian

I noticed a similar miss today in mine as well. Right a the shift point. Looks like I will be looking into this as well. Beep

The tach can defintely cause problems. Have run in to it a few times. Try removing the wire from ignition box to see if problem goes away. Only run shift light in my car for that very reason.Had a miss that would come and go,and tach needle would bounce around.

"I can pull the high side chip out of two step and the "miss" goes away."
72cudaracer I have a msd digital 7 and I could try and pull the high side out of my 2 step to see if it goes away like yours did but if it does that would probably indicate that something was wrong with the msd box.I also have my 2 step at 4500 and the problem occurs closer to my shift point(6500 rpm) I have already replaced it (box)thinking it could be bad and unless I have 2 bad boxes that probably is not my problem?
I am probably going to replace the tach to see if it fixes it! It will be relatively cheap compared to what I have already done so far!
The fact that others have had similar problems leads me to believe this could be IT!
Thanks Mike
p.s. The only other thing I have not replaced is my linelock button on my shifter.It is pretty old and I suppose that when I shift it could be making slight contact and activating my burnout rev limiter for that fraction of a second.

70sat guy,
All it will cost me is some time. I have a new tach in the box I bought for my other car thats not finnished. I'll change it out and try to run it Fri night at TnT, if it don't rain. I'll post results if/when I do.
Brian

I have had a bad tach cause a car to miss above 3000 RPM Any elecrical component on the car hook to the ignition can and (if it is me ) will cause problems try doing the process of eleiminatios as already suggested, remove one component at a time, tach first, shift light and so on. I have also seen MSD chips go bad and cause a mis at a lower RPM than written on the chip Good luck, let us know what you find and the cause

I have also seen some of the MSD chips that were much
less rpm that they were rated at... try a different
chip
EDIT
Also poor grounds will cause issues