tach accuracy | Ford Explorer Forums - Serious Explorations

  • Register Today It's free!

tach accuracy

mysticclam

Typo King
Joined
April 2, 2004
Messages
210
Reaction score
0
City, State
Tacoma, WA
Year, Model & Trim Level
91 XLT
my 91 explorer has 4.56 gears and 33inch tires. Every calculator or chart ive come across says 5th gear 60 mph should be about 2200 rpm. My tach reads 2850ish seems really high. Engine kind of sound like 2850ish though
I have checked the speed with GPS as my speedo is off (it is off the right amount, when gps says 60, speedo reads 69 which is just the right amount off.
Tach on a 91 is pretty basic right? my gear and tire swap shouldnt have affected it at all. I cant remember if it seemed high before, it was a long time ago.
I was wondering if there was a switch or something for 4 cyl engines (same dash used in 4 cyl rangers) they had 8 plug heads, divide my rpm by 8 and multiply by 6 and you get pretty close to the expected 2200 rpm. Any way to check if I have a 4cyl tach or if you can switch it?
 






As I've found out recently, the tach's can be way off as yours is, especially 1991 for some reason. Both my 94's are dead on. You are correct in your RPM calculation, and it is where your RPM's actually are.
 






I have 4.88's and 35's and my tach reads almost 3K at freeway speeds. Ive daily driven my truck for a long time before the gear and tire change and I am positive that it is a lot closer to 2K.
 






I might put in an aftermarket tach in to see if i can get a true reading but im the kind of person that would go bonkers looking at two tachs, especially if they read differently. I dont use the truck too much but I like it so I keep it for fun. Figured I might drop a v8 in mostly for something to do with it. Thought a c4 might keep it simple but was thinking if my tach isnt really wrong losing overdrive would mean astronomical rpms on the highway.
 






Back
Top