Howdy all,

My son's tach works most of the time but often hangs up. For example say we're driving at 2000 rpm's, then look down and it stuck at 5000. But it was never reved to 5000. Its like it jumps up and hangs up but after 15 or 20 seconds it starts working again.
I read some posts about the old RX's taping off of the spark coils for the reading for the tach. Is this the case for 93's? Can anyone give me a hint on how the tach is set up? Or if anyone has had this issue.

thanks

 

I was about to post up about this as well. How long has it been doing this? Mine was going back and forth between working and not at first. Now it just does what it wants. When I turn it off it usually settles down at 9 instead of 0. I found this fix but not sure if it would help my problem but may be of use for you.

http://www.wrex-racing.com/docs/fd/Tach_Repair.pdf

 

If you search you can find out lots about this common problem...

This problem is not specific to the '93's.
As was pointed out in the prior email cold solder joints are the cause.
You can either get a replacement tach from the parts section (gauge faces are different for 93 and latter tachs) or fix it yourself but as indicated in the provided link it is not a procedure for the faint of heart.

 

replacing the tach is ver easy. I would just replace the tach with a '94. Just take out the gauge cluster....theres a writeup on the web on how to remove the cluster. Takes about 25mins to get out first time. Unscrew the tach from the back and take it out. Replace. Install screws. Done.

I'm upgrading my cluster and I'd be willing to sell my 94 tach by itself if you are interested. My car is at the tranny shop right now, but I should be getting it back shortly and I'll be pulling the cluster.

 

I think that a bad solder connection seems to fit with the way its acting. I will try to dismantle the dash and see if I can get too it. One of the links above to take apart the dash was missing. I'm on vacation in Montana now for a couple weeks so I'll have to get to it maybe mid july. Thanks everyone...

 

My brother and I were unsure if replacing the solder joints would solve my problem. My symptoms aren't the same as the write up and duder's. My tach doesn't work ever. When you turn the car off it settles at 9 instead of 0. While the car is running it chooses it's own rpm and doesn't move around, every so often it just switches which rpm it stay stagnant at.

 

Sounds like the gauge "pointer" is loose on its shaft ......

 

I think the pointer is ok, the car at idel will jump to 5k rpm's and hang there then drop back again. I think it is probably electrical in nature.

Is there a substitue replacement for the RX7 tach? I found a lot of 626's in the junk yard, would the internal parts be the same? I found the passenger power window switch is the same. Just a thought.

duder

 

Oops, time for an update.....
I found instructions somewhere and pulled the tach out.
It had little ring like cracks around the discrete components, the ones with legs not the surface mount ones.
I re soldered all of them including the IC legs and put it back together and it works just dandy!
You'll need a very sharp tip soldering iron, I sharpened mine on the grinder.
Be careful this requires a lot of cursing and super patients.

 

This happened to me before.

Check that your spark plug wires and not split or ripped. Mine were and arched to the block causing my tach to jump.

Also, if that doesnt work. You can try to resolder all solder joints in the back of your cluster.

Once youve tried both of those, I guess you could just go and replace your tach, they are not that expensive these days.

 

I got one off Fritts and solved this issue. At some point my brother is going to fix mine since there is a color difference.