Tachometer shows idle as 4000 rpm

Just bought a used 05 regular cab base,2.7 and 5 speed.
Its the plain truck.No cruise control,manual windows and locks.

Anyway Ran great for first 200 miles,tach was normal.

Taught my 13 year old son to drive a standard,rode for about an hour with me perfecting take off on first.Nothing over 2000 rpm,lol lots of staling.

Turned him loose in the yard by himself,1st gear only pratice start and stop.

After about 40 minutes he came back and said tach was acting weird.

At idle which was about 800 rpm,the tach is showing 4000 rpm,even when truck is off it wont drop lower than 4000 rpm.

I tried search function but I had no luck getting it to work.

 

Damn. Subd for outcome.

 

I'm assuming the truck really isn't at 4k?

So you are asking about dealing with a funky tach?

 

what about when you turn the truck off? stays at 4k?

 

Engine is at normal idle,tach starts at 4k

Engine off tach acts as if 4k is the zero point

 

I'd pull the tach and experiment with the needle mechanism to see if it's clean and free moving. Even a drop of light machine oil if you see a place to do that.

Otherwise, I'd look for a junkyard cluster and swap in the 'new' tach.

Or if its a real budget rig, just ignore the fact that it doesn't work. It's user eye candy for the most part.

How many miles on the truck? What kind of 'life' has it led?

 

tach is either broken or the cable that receives the reading has become disconnected from one end(if there is no cable then correct me someone)

 

Stepper motor.

 

110k miles,I dont use tach anyway,I shift by feel and sound.1800-2000 rpm.Im a gas saver.
Don't know history of the truck.Bought it used from a dealership

 

I let it sit awhile and keep checking on it,it returned to zero slowly,ticking like a stepper motor

 

ouch haha i must be wrong. i thought my data might be dated

 

So after about 1/2 or running the rim drops to a lower reading.
So there is an issue I'll have to investigate.
Maybe clean a sensor,voltage issue.

I'll keep it posted as I troubleshoot.