Tach Not working properly

[pcpotter]

Hey guys I could use some help, I have a 1991 F250 with a 5 speed tranny and from time to time the tach does not work properly, I've been watching it for a year now trying to see some type of repeats or different times that it does not work and times when it does work and I have noticed that when it is cold outside or before the truck gets warmed up is when it appears to not work the most it is really bad when it is cold outside. Can y'all give me some advice as to what to look for or where to start. It does show RPM but it is not even close to accurate until it warms up.

And Again Thanks for y'all help.
Patrick

 

[towcat]

90% of the tach problems is found in the tach sensor.
goto the stealership and get yourself a new one.