Crazy Tach!

[2oldschool]

The tachometer in our 90 L98 has gone from 2000 at idle to 6000 at 70 mph.I checked the idle rpms with a tester & it read 850 rpms .Is the filter the problem?If it is where can I buy a new one? Thanks.

 

[GWinter]

I have a 90 and my tac has gotten off farther all the time. I did some research a few yrs ago and the tacs in some yrs corvettes have a bank of resistors in them and one or more of those will fail. There is a way to repair them (found on youtube) but is a time consuming project.Have never tried locating a replacement.

 

[DonB]

I have a '90 coupe and had the same issue with the tach. I replaced the tach filter with a replacement from Corvette Central. It is a "bear" to change and in my case did NOT fix the problem. But it's a chance. More than likely....

You have to fix the circuit board behind the tach. Search for tach repair. There should be a bunch of articles here on it. I just cant find mine right now. You have to dis assemble the dash cluster and remove the circuit board. I then took mine to my local TV repair guy and he bypassed the bad resistors and soldered in new resistors. Now the tach is accurate as can be. Check my next post here for photos and instructions. It'll take me a bit to dig up the info.

 

[DonB]

Here's the link to another forums' post. There are some good pictures. I will also post mine.
94 Vette Tachometer Problems - Corvette Forum

Here are mine I kept as a record. Note: Be sure replacement resistor(s) total 300k or very close to it. The second picture is my arrangement. Worked like a charm.

 

[GWinter]

Thank you for posting that I need to take my dash apart to replace the heater core so it will be a good time to repair the tach also.

 

[DonB]

Thank you for posting that I need to take my dash apart to replace the heater core so it will be a good time to repair the tach also.

Good Luck G! If you get stuck, shoot me a PM and I'll help you out if I can.

Also, something to consider while the dash is out...If you have the Delco GM-Bose system, they CAN be very temperamental and DIE suddenly.....There have been a ton of posts on it.

As a matter of fact; Tomorrow I'm installing the Pioneer 720 double DIN receiver with JBL's and an Alpine amp in mine. I'm looking forward to the Bluetooth connectivity and dumping the disc changer that seldom works. My receiver has been fading in and out plus jumping channels for a while so I figure it is on it's way south.

 

[GWinter]

I don't use my radio/stereo enough to even know for sure if it works. lol But I am going to look for missing screws , cracks and places where I can insulate to get rid of dash noise.