Jump to content

Tachometer sticks and jumps


KentWood
 Share

Recommended Posts

I have a 1990 TC

My tachometer is reading funny.

It seems to stick, and then will jump if I accelerate at idyl.

When I shut off the engine it will not go to zero.

How does this thing work ? I could not find any information in the service manual.

What could cause this ?

From what I read on this forum it is not driven by a cable from a gear on the transmission to the instrument itself: is that correct ?

Click on thumbnail for larger picture.

post-70130-143138697471_thumb.jpg

Link to comment
Share on other sites

The tach is driven electrically by a small PC card which plugs into the upper rear side of the instrument cluster. It takes a signal from the engine computer and converts it to a signal which drives the tach, which is basically an analog type meter (magnet and coil driving the needle). If it freezes at times, or goes up with engine speed and stays there like it's sticking, it's likely the PC card contacts are either dirty, loose, or the card is inserted wrong (it can be put in at an angle which makes it work intermittently). If it just jumps around on its own, the signal from the computer is noisy, or possibly the wire for that signal is loose.

I'd check the connections at the computer and the instrument cluster. You can sometimes fix this kind of thing just by un-plugging and re-plugging the connectors.

Jim

Link to comment
Share on other sites

Jim,

You wrote:

I'd check the connections at the computer and the instrument cluster. You can sometimes fix this kind of thing just by un-plugging and re-plugging the connectors.

Generally, how do I do this? Must I remove the instrument cluster or is there a simpler way ?

Link to comment
Share on other sites

Unfortunately, they are behind the cluster. It's not too difficult to remove, the toughest thing is getting the headlight knob off - there are several how-tos in the forum on this. Search for "cluster removal" and there are a number of good posts on this.

Basically the cluster cover is held in with two screws at the top of the round cover (from underneath) and with screws into the dash that are under the left and right trim on top of the dash. The cluster itself is held in with screws top and bottom which you can easily get to after the cover comes off.

If it's not clear from the posts, let me know and I can take some photos when I get some time...

Jim

Link to comment
Share on other sites

  • 3 months later...

I know this post is much later than the last, but there's another possibiity too. That's the braided ground strap that connects and bonds the rear of the intake manifold to the firewall on the passenger side. This strap needs to be secure as does the injector ground wires that attach to one of the two 10mm bolts that secure the fuel rail to the manifold.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...