Tach reads odd

[scotts90ranger]

Hello,

I did a search, and didn't come up with anything...

the tach in my explorer is off by a lot (say 20% or so). The thing is supposed to have 3.55 gears and it has 235 75 15's like is stock on a '91 sploder but in 5th gear at 55 it says around 3300rpm which is WAY off from what it should be, also says it idles at 1200 or so (and I know it's in the 8-900 range like it should be, doesn't sound like 1200). I don't think the gears have been changed but turning that kind of rpm's it would have to have 4.88's or so and it definetely doesn't have them...

any ideas? the main chassis ground from the battery is in bad shape but that's mainly an issue in starting, the thing runs good, gets 16-19mpg like it should, runs smooth just with an inaccurate tach...

thanks

 

[scotts90ranger]

anyone?

would it be a bad coil pack? that's about all there is to the ignition system right? is there a separate ignition module? I don't remember seeing one...

 

[scotts90ranger]

really? no-one has any ideas? I've looked around and didn't see a separate ignition module like on the 2.3...

 

[Sasquatch_Ryda]

For some odd reason when it gets cold out, my tach reads really high and jumps RPM very rapidly. After about 10 minutes of driving it drops back down and goes back to normal.