Hey guys,

I just bought a 1990 RS with a TBI 305. My problem is the tach is way off. It reads 4000 rpm when the motor is at 2000. It's real bad. I thought maybe it was originally a 6 cylinder car, but the vin states it is an 8, and the stickers under the hood all say 5.0 liter. Is it the wrong cluster? Any ideas?

Thanks!

Randy

 

It's definitely possible that it's the wrong cluster, but it's really not all that uncommon for the tach to read way off. I see posts like this at least one a week. Mine reads about 1000 RPMs to high at all times.

There have been many posts about possible fixes, and replacing a certain capacitor on the back of the tachometer usually fixes the 82-89 Camaro tachs, but I have yet to see it work on the 90-92 Camaro tachs. The only true fix that I have seen so far is to send the cluster to a shop that specifically works on repairing factory gauge clusters and instrument panels.

It might be worth it to try another gauge cluster just to see, but I wouldn't be surprised if the one you buy has a "wacky" tach, too.

 

Ok, I just bought my second third gen yesterday..

Its a 1991 RS L03 Car, and its tach is off too.

First off.. I realize that these tachs were never intended to be "accurate" and were more of just an eye pleaser but thats not the point, the point is i would like the tach to function properly with the factory guage, without having to replace the whole cluster.


That being said, I know also that there has been a fix found for pre 90 tachs..

question now is do we know how to fix these tachs? do we have a way to tell what is wrong? Can we get the parts... Can we fix it inexpensively?



-steve.

 

no one? i cant belive that no one has any solution.
-steve

 

I have EXACTLY the same problem. It started out just reading about 1000 too high, then 2000, 3000, 4000, now when idling it's almost pegged, and when I rev at all it's off scale. The engine runs fine.

 

I forgot to mention, I bought the car (1991 RS) NEW and it worked fine for 11 years then started going up, up, up!!! since no one has fixed it, I will investigate and post what I find.

alhiggs

 

allright al.. let me know what your able to find out. Im sure theres a way out there, i just dont konw enough about electronics to get into it and find the problem.
thanks
-steve

 

my 89 rs was fine for the first 12 years. Now it idles at 1500.
cruises at 55 mph at 5500 rpm and is pegged anytime I need to get up and go.

Let me know what you find.

 

any good news yet? or bad news for that fact?

thanks

-steve

 

check this link out. It seems to be a capacitor in the tach that goes bad. I will try this out sometime this summer. Working on getting my z-28 on the road first.

 

maybe its just my comp acting up but i don't see the link in the above post.
i have the same problem w/ my tach. idle read 6800. would love to know where the capaciter (cant spell) is located and replace it. thanks for the help.

 

Ok Guys,
I took it apart and found that:

1) I have a system that I have not seen on this thread yet. The gauge itself is a standalone plug-in meter (with a common-connected 2-coil movement, permanant magnet I presume, with no spring at all, and can go a full 360 if you remove the stopper peg.

2) Mine (1991 RS) has a small driver board that plugs in at the lower right hand side of the gauge assy.

3) There are no bad components that I could find (IN circuit testing only)

4) I DO get a [very noisy] tach signal at pin 1 of the connector that comes from the primary side of the coil, as observed with my scope.

My situation: The Chevy dealer nearest me said they COULD fix the problem but it would cost over $350. The car is only worth about $900 really so I did some experimenting myself:

1) I measured the DC resistance of the coils on the gauge. 220 ohms for coil 1 (X) and coil 2 (Y)

2) I found that by applying a DC signal (-12V to +12V) on each coil that I could make the meter go any position 360 degrees, even around and around.

3) I rigged up an H-Bridge circuit to drive each coil anywhere from +12V to -12V using PWM, and a microcontroller, and was able to position the meter.

4) I wrote a small program to time the pulses from the primary ignition coil and move the meter to where it should be depending on the RPM.

It worked. Once I calibrated it, it was very accurate. But I ran out of time (I'm moving and had to put it all in a box). I decided that I was going to try and design a board that could be installed to replace the driver board, but I'd do it later as it would take some time. If there is enough interest, I would make available what I've done so far, as a cheap replacement for the Chevy driver board. Heck, the microcontroller I used only costs about $3.... and the H-Bridge maybe only a dollar or two.

Let me know if y'all are interested, and I'll pursue it.

Austin

 

Interested, it seems to me that calibration would be of no use until Step # 4 investigated. Thanks

 

im intersted.. however, that being said, I want a PNP application.. I want to just buy the replacement / add on, and install it and be done with it..

lemme knwo what you come up with..
-steve

 

gauges for these cars simply dont work on the highway my speedo wraps around all the way into metric and bounces my tach hasnt moved since i bought the car. i gave up drove down the street to summit and bought both for $100 and installed them on my dash leaving the old ones in place.