Ok here is another weird one for ya guys. Over the winter I rebuilt the motor on my teg. I also replaced the oem distributor with a MSD dist. The kit came with the external coil pak and a coil driver box. Installed them and now my factory tach does not work. MSD conveniently places a external tach wire off of the distributor. Tapped into it and ran a hard wire to the tach tap-in on the inside of the engine compartment…factory tach still does not work??? all fuses are good and everything else in the gauge cluster is working properly…any ideas?
P.S. car runs fine so all boxes are installed correctly.
I’m assuming it worked fine previously, as in pre-MSD?
The OEM dizzy has the CKP/CYP sensors built into it, which are the signal for the tach. That pretty much means you are now missing one or both now. I’m not terribly familiar with MSD stuff, since I don’t have any use for it, but I’d call them and ask.
Tachometer ('98-'99 Models)
The tachometer drive circuit receives oulses from
the ignition control module (lCM) in the distributor
assembly. The solid-state tachometer then displays
these pulses as engine speed. For each 200 pulses
per minute from the ignition control module (lCM),
the tachometer displays 100 RPM.
Tachometer ('00 Model)
The tachometer drive circuit receives pulses from
the PCM or ECM. The solid-state tachometer then
displays these pulses as engine speed. For each
200 pulses per minute trom the PCM or ECM the
tachometer displays 1 00 RPM.
Unfortunately there is zero mention of voltages, and I’ll bet you can’t even check it since it’s not sending anything out. That servie tach port is the most direct connection to the ICM unit. I’d guess here, but .5 to 5ish volt sweep?
yes it worked fine pre MSD…made a phone call to MSD they said it should work and to try and hard wire it to the auxiallary tach output off of the dizz, which already has been done…??? I think Im just going to buy an A/m tach and try it.
you may need to replace the oem tach with a new one for it to match up to the ms crap…as the oem uses a specific signal that the ms probly doesent provide…good luck…keep us posted.
when i had tach problems last summer, just for giggles i actually measured the signal to see if it was actin goofy from the distributor. i believe it was between 1volt and 1.9volts… fluctuating up and down for different rpm’s and i think it was seemingly backwards like 1.9v was around 1,000rpm and 1v was up neer the 8,000rpm area
that could be completely backwards though so i’m not much help
Aren’t tach signals usually a square wave of some sort? Depending on what you used to measure that signal that all could be junk data. A multimeter or volt meter will not measure a square wave accurately as there is a sample rate, then an averaging that takes place. You would need a scope to read that type of signal.
i appreciate all the help, like i said earlier just bought a big gay homo tach and installed it so im just going to use it… now i have a supa fast wace car!
now i have a supa fast wace car!