turbozo6

After getting a few problems straightened out I have discovered another one. The car is a '91 RS Camaro with 305tbi and auto trans. I had a new fuel pump and sending unit installed on the car and now I have noticed the the tach isn't reading correctly. It seems to be reading really high. At about 30mph it is reading about 3500rpm and at 70 it is about 5200. The engine obviously isn't turning that fast. I have driven the car for years and know about how the engine should sound at a given rpm. Anyone have any ideas?

camarito

my 84 was doing the same thing, got a new/used gauge cluster on Ebay and it's good now

Vader

This is a very common situation resulting from a misunderstanding of the intent of the instrument cluster.

When the car was designed, the Fisher Body interior design art department laid out the interior and drew up a really nice looking gauge cluster. However, the "chi" of the space required it to have one extra hole for aesthetic balance and the proper feng-shui, and they scrambled to find something to fill the space. They decided to install an instrument which would show the relative speed of the engine with an indicator needle which could rise and fall as the engine would spin faster and slower. Someone from Accounting Services was assigned to put some markings on the instrument since the team decided it should look like the other gauges as much as possible, so some numbers were randomly placed around the perimeter. A second associate student intern engineering assistant mentioned that the numbers should probably be sequential, so they were placed in some incremental order. Thus, the GM Relative Powertrain Motion (RPM) gauge was born. Anyone who has ever used, read about, installed, observed, or can spell the word "tachometer" understands that the GM RPM gauge isn't a tachometer, but a relative indication of whether the engine is turning. It's the best that the Interior Design Art, Marketing, Accounting, Overstocked Parts Department, and an engineering intern could come up with.

In a nutshell, you're lucky it even moves. Some of them accidentally display a number that is even pretty close to actual engine RPM (not "GM RPM" but revolutions per minute).

There are ways to fix it, and there are numerous threads on these boards addressing the situation. If you had used the SEARCH function you could have saved yourself all the trouble of reading all this drivel.

Vader

Or you could just skip directly to this thread:

https://www.thirdgen.org/forums/elec...meter-fix.html